The neuroleptic malignant syndrome (NMS) is a rare complication in response to neuroleptic or antipsychotic medication.

The main features are:
– Elevated creatinine kinase
– Hyperthermia and tachycardia
– Altered mental state
– Increased white cell count
– Insidious onset over 1-3 days
– Extrapyramidal dysfunction (muscle rigidity, tremor, dystonia)
– Autonomic dysfunction (Labile blood pressure, sweating, salivation, urinary incontinence)

Management is supportive of ICU care, anticholinergic drugs, increasing dopaminergic activity with Amantadine, L-dopa, and dantrolene, and non- depolarising neuromuscular blockade drugs.

Since Olanzapine is a potential cause of NMS it is not a treatment.

Ampicillin belongs to the family of penicillin. Resistance to this group of drugs is due to β-lactamase production which opens the β-lactam ring and inactivates Penicillin G and some closely related congeners. The majority of Staphylococci and some strains of gonococci, B. subtilis, E. coli, and a few other bacteria produce penicillinase.

Resistance to cephalosporins is due to changes in penicillin-binding proteins.

Resistance to macrolides are due to post-transcriptional methylation of 23s bacterial ribosomal RNA

Resistance to fluoroquinolones is due to mutations in DNA gyrase.

Barbiturates are derived from barbituric acid, which itself is nondepressant, but appropriate side-chain substitutions result in CNS depressant activity that varies in potency and duration with carbon chain length, branching, and saturation.

Oxybarbiturates retain an oxygen atom on number 2-carbon atom of the barbituric acid ring.

Thiobarbiturates replace this oxygen atom with a sulphur atom, which confers greater lipid solubility. Generally speaking, a substitution such as sulphuration that increases lipid solubility is associated with greater hypnotic potency and more rapid onset, but shorter duration of action.

Addition of a methyl group to the nitrogen atom of the barbituric acid ring, as with oxybarbiturate methohexital, also results in a compound with a short duration of action.

Oxygen delivery is related to blood flow as most of the oxygen binds to haemoglobin in red blood cells, although a small amount is dissolved in the plasma. Blood flow per 100 g of tissue is greatest in the kidneys.

The following is the oxygen consumption rate of different organs in ml/minute/100g

Hepatoportal = 2.2
Kidney = 6.8
Brain = 3.7
Skin = 0.38
Skeletal muscle = 0.18
Heart = 11.

Ambient pressure has no effect on a volatile agent’s saturated vapour pressure (SVP). At a temperature of 20°C, the SVP of sevoflurane is approximately 21 kPa, or 21% of atmospheric pressure (100 kPa).

The SVP of sevoflurane remains the same when the ambient pressure is doubled to 200 kPa, but the output of the vaporiser is halved, now 21 percent of 200 kPa, equalling 10.5 percent. The vaporiser’s output has increased to 1%, but the partial pressure output has remained unchanged. The splitting ratio will not change because it is determined by temperature changes.

Calculations can be made as follows:

Vaporizer output % (ambient pressure) = % volatile (calibrated) x 100 kPa calibrated pressure/ambient pressure
2% = 2% (dialled) × 100/100
2% of 100 = 2 kPa

Altitude, pressure 50 kPa
4% = 2% (dialled) × 100/50
4% of 50 = 2 kPa

High pressure at 200 kPa
1% = 2% (dialled) × 100/200
1% of 200 = 2 kPa

Sevoflurane has a boiling point of 58°C and, unlike desflurane (which has a boiling point of 22.8°C), does not need to be heated and pressurised with a Tec 6 vaporiser.

Cardiac output = stroke volume x heart rate

Left ventricular ejection fraction = (stroke volume / end diastolic LV volume ) x 100%

Stroke volume = end diastolic LV volume – end systolic LV volume

Pulse pressure = Systolic Pressure – Diastolic Pressure

Systemic vascular resistance = mean arterial pressure / cardiac output
Factors that increase pulse pressure include:
-a less compliant aorta (this tends to occur with advancing age)
-increased stroke volume

The AV node has an intrinsic firing rate of 40-60 beats per minute which is clinically significant in cases of damage to the conducting pathways as patients continue to have a ventricular rate of 40-60. Patients who have an AV node supplied by the right coronary are said to be right dominant. The remaining 10% are left dominant and supplied by the left circumflex.

The right coronary artery supplies the right atrium, right ventricle, interatrial septum, and the inferior posterior third of the interventricular septum. It also supplies the atrioventricular node + sinoatrial node in most patients. The posterior descending artery supplies the posterior third of the interventricular septum.

The heart receives blood supply from coronary arteries. The right and left coronary arteries branch off the aorta and supply oxygenated blood to all heart muscle parts.

The left main coronary artery branches into:
1. Circumflex artery – supplies the left atrium, side, and back of the left ventricle. The left marginal artery arises from the left circumflex artery. It travels along the obtuse margin of the heart.
The left marginal artery, a branch of the circumflex artery, supplies the left ventricle.
2. Left Anterior Descending (LAD) artery – supplies the front and bottom of the left ventricle and front of the interventricular septum

The right coronary artery branches into:
1. Right marginal artery
2. Posterior descending artery.

Arterial pressure waveforms is an invasive form of monitoring cardiac parameters. It provides a lot of information on the performance of the heart from different sections, including:

Cardiac measurements:

Heart rate
Systolic pressure
Diastolic pressure
Mean arterial pressure
Pulse pressure
Change in pulse amplitude corresponding to respiratory changes
Slope of anacrotic limb associated with aortic stenosis

From the shape of the arterial waveform displayed:

Slope of anacrotic limb represents aortic valve and LVOT flow
Indications of aortic stenosis (AS): Slurred wave, collapsing wave
Rapid systolic decline in LVOTO
Bisferiens wave in HOCM
Low dicrotic notch in states with poor peripheral resistance
Position and quality of dicrotic notch as a reflection of the damping coefficient

For this question, the upstroke slope of the pressure wave is indicative of myocardial contractility and is mathematically represented as:

dP/dt, which represents a change of pressure with regards to time.

The Delphi method relies on expert consensus. This method kicks off with an open ended questionnaire and uses its responses as a survey instrument for the next round in which each of the participants is asked to rate the items that the investigators have summarized on the basis of the data collected in the first round. Any disagreement is further discussed in phases to come on the basis of information obtained from previous phases.

Amiodarone is the longest-acting anti-arrhythmic drug. It possesses the action of all classes of antiarrhythmic drugs (Sodium channel blockade, Beta blockade, Potassium channel blockade, and Calcium channel blockade). Due to this property, it has the widest anti-arrhythmic spectrum and thus can be used in both broad and narrow complex tachyarrhythmia.

Adenosine is shortest acting anti-arrhythmic drug.

The derived unit of energy, work or amount of heat is joule (J). It is defined as the amount of energy expended if a force of one newton (N) is applied through a distance of one metre (N·m)

J = 1 kg·m/s2·m = 1 kg·m2/s2 or 1 kg·m2·s-2

Kinetic energy (KE) = ½ MV2

An object with a mass of 1500 kg moving at 30 m/s correlates to 675 kJ:

KE = ½ (1500) × (30)2 = 750 × 900 = 675 kJ

Total energy released when 1 kg fat is metabolised to CO2 and water is 37 MJ. 1 g fat produces 37 kJ/g, therefore 1 kg fat produces 37,000 × 1000 = 37 MJ.

Raising the temperature of 1 kg water from 0°C to 100°C correlates to 420 kJ. The amount of energy needed to change the temperature of 1 kg of the substance by 1°C is the specific heat capacity. We have 1 kg water therefore:

4,200 J × 100 = 420,000 J = 420 kJ

In order to calculate the energy involved in raising a 100 kg mass to a height of 1 km against gravity, we need to calculate the potential energy (PE) of the mass:

PE = mass × height attained × acceleration due to gravity
PE = 100 kg × 1000 m × 10 m/s2 = 1 MJ

The heat generated when a direct current of 10 amps flows through a heating element for 10 seconds when the potential difference across the element is 1000 volts can be calculated by applying Joule’s law of heating:

Work done (WD) = V (potential difference) × I (current) × t (time)
WD = 10 × 10 × 1000 = 100 kJ

Parotidectomy is basically an anatomical dissection. Identification of the facial nerve trunk is essential during parotid gland surgery because facial nerve injury is the most daunting potential complication of parotid gland surgery owing to the close relation between the gland and the extratemporal course of the facial nerve. After exiting the stylomastoid foramen, the facial nerve enters the substance of the parotid gland and then gives off five terminal branches:
From superior to inferior, these are the:
– Temporal branch supplying the extrinsic ear muscles, occipitofrontalis and orbicularis oculi
– Zygomatic branch supplying orbicularis oculi
– Buccal branch supplying buccinator and the lip muscles
– Mandibular branch supplying the muscles of the lower lip and chin
– Cervical branch supplying platysma.

There are two approaches to identify the facial nerve trunk during parotidectomy€”conventional antegrade dissection of the facial nerve, and retrograde dissection. Numerous soft tissue and bony landmarks have been proposed to assist the surgeon in the early identification of this nerve. Most commonly used anatomical landmarks to identify facial nerve trunk are stylomastoid foramen, tympanomastoid suture (TMS), posterior belly of digastric (PBD), tragal pointer (TP), mastoid process and peripheral branches of the facial nerve.

The superior laryngeal nerve gives off two branches: the sensory branch which is the internal laryngeal nerve, and the motor branch which is the external laryngeal nerve.

The recurrent laryngeal nerve (RLN) rises from the vagus nerve which supplies the intrinsic muscles of the larynx, except the cricothyroid muscles.

The ascending cervical artery lies media the phrenic nerve on scalenus anterior and can easily be mistaken for the phrenic nerve at operation.

The phrenic nerve passes across scalenus anterior and medius inferiorly.

The subclavian artery is separated from the vein by the scalenus anterior.

The brachiocephalic vein is formed at the medial border of scalenus anterior by the subclavian vein and the internal jugular vein.

Emerging from the lateral border of scalenus anterior are the trunks of the brachial plexus .

The structures in the porta hepatis from anterior to posterior are:

The ducts: Most anterior are the left and right hepatic ducts.

The arteries: Next are the left and right hepatic arteries

The veins: Next is the portal vein

The epiploic foramen of Winslow lies most posterior at the porta hepatis.

Tachyphylaxis is the swiftly declining response to successive drug doses which vastly reduces its effectiveness in a short space of time, mostly as a result of an acute consumption of neurotransmitters.

Tolerance or desensitisation is the slow decline in a person’s reaction to a drug due to continued use. It requires a longer time span than tachyphylaxis, usually over days or weeks.

Down- regulation is a reduction in the amount of receptors available on target cells which decreases the affinity of the agent to the cells. For this to occur, the down-regulation of receptors must occur at a rate faster than receptor synthesis. This down-regulation often occurs with beta1 receptors due to:

1) The transportation or receptors from the cell surface to the interior of the cell

2) Degradation of receptors occurring over time.

In this case, dobutamine is prescribed to treat cardiogenic shock. It is able to function by binding to beta1-adrenergic receptors to increase the contraction of the heart, thereby improving cardiac output. It also binds to beta2- and alpha1-adrenergic receptors to balance out the effects produced by binding to beta1 receptors and reduce the risk of system vasculature responses.

Because enflurane is much less soluble in blood and has a blood: gas partition coefficient of 1.8, both wash-in and wash-out should be faster.

Sevoflurane’s sweet-smelling, non-irritant nature, combined with a low blood: gas partition coefficient, would result in similar offset and onset characteristics.

Isoflurane and enflurane have a molecular weight of 184.

The oil: gas partition coefficient on a volatile agent is a measure of lipid solubility, potency, and thus MAC. Halothane has an oil: gas partition coefficient of 220 and a MAC of 0.74. One would expect the MAC to be higher with an oil gas partition coefficient of 180 (less lipid soluble).

The conversion of halothane (20%) to trifluoroacetic acid via oxidative metabolism has been linked to the development of hepatitis.

P450 2E1 converts sevoflurane to hexafluoroisopropanol, which results in the release of inorganic fluoride ions. It’s the only fluorinated volatile anaesthetic that doesn’t break down into trifluoracetic acid.

Desflurane is likely to cause airway irritation, which can lead to coughing, apnoea, and laryngospasm, despite its low blood:gas partition coefficient (0.42).

Triiodothyronine (T3) is more potent than thyroxine (T4). It is able to bind to more receptors (90%) compared to T4 (10%), and the onset of action is more immediate (within 12 hours) than T4 (2 days).

Ninety-three percent of thyroid hormones synthesized is T4, and the remaining 7% is T3. The half-life of T3 is shorter (1 day), and its affinity for thyroxine-binding globulin is lower than T4.

The international system of units, or system international d’unites (SI) is a collection of measurements derived from expanding the metric system.

There are seven base units, which are:

Metre (m): a unit of length
Second (s): a unit of time
Kilogram (kg): a unit of mass
Ampere (A): a unit of electrical current
Kelvin (K): a unit of thermodynamic temperature
Candela (cd): a unit of luminous intensity
Mole (mol): a unit of substance.

Atrial natriuretic peptide (ANP) is secreted mainly from myocytes of right atrium and ventricle in response to increased blood volume.
It is secreted by both the right and left atria (right >> left).

It is a 28 amino acid peptide hormone, which acts via cGMP
degraded by endopeptidases.

It serves to promote the excretion of sodium, lowers blood pressure, and antagonise the actions of angiotensin II and aldosterone.

Wavelength can be computed as follows:

Wavelength = velocity/frequency

In the given problem, the values stated are:

Frequency = 10 x 10^6
Velocity = 1540 meters per second

Wavelength = 1540/(10×10^6)
Wavelength = 1540/10,000,000 meters
Wavelength = 0.15 millimetres.

Anticholinergic agents are a group of drugs that blocks the action of the neurotransmitter called acetylcholine at synapses in the central and peripheral nervous system.

Hyoscine, atropine, and glycopyrrolate are anticholinergic which acts at muscarinic receptors with little activity at the nicotinic receptors.

Hyoscine and atropine are naturally occurring esters. Since Glycopyrrolate is a synthetic quaternary amine, it does not cross the blood brain barrier. Noteworthy, hyoscine, butylbromide also does not cross the blood brain barrier significantly.

The Weibull distribution are used to describe various types of observed failures of the components. it is used in reliability and survival analysis.

Regression Analysis is used to measure the relationship between among two or more variable. It determines the effect of independent variables on the dependent variables.

Student t-test is one of the most commonly used method to test the hypothesis. It determines the significant difference between the means of two different groups.

A time series is a collection of observations of well-defined data obtained at regular interval of time.

Kaplan-Meier estimator is used to estimate the survival function from lifetime data. It can be derived from maximum likelihood estimation of hazard function. It is most likely used to measure the fraction of patient’s life for a certain amount of time after treatment.

The renal effects of atrial natriuretic peptide (ANP) secretion are as follows:

Increased glomerular filtration rate by dilating the afferent glomerular arteriole. Moreover, it constricts the efferent glomerular arteriole, and relaxes the mesangial cells.
Reduces sodium reabsorption in the collecting ducts and distal convoluted tubule.
The renin-angiotensin system (RAS) is inhibited.
Blood flow in the vasa recta is increased.

Because plasma osmolality is unlikely to change, hypothalamic osmoreceptors are unaffected.

The plasma protein has a molecular weight of 66 kDa, is not normally filtered into the proximal convoluted tubule, and has no osmotic diuretic effect.

The following are some basic assumptions:

Extracellular fluid (ECF) makes up one-third of total body water (TBW), while intracellular fluid makes up the other two-thirds (ICF)
One-quarter plasma and three-quarters interstitial fluid make up ECF (ISF)
The volume receptors in the atria have a 7-10% blood volume change threshold.
The osmoreceptors are sensitive to changes in osmolality of 1-2 percent.
The normal plasma osmolality before the transfusion is 287-290 mOsm/kg.
The plasma protein solution is a colloid that is only delivered to the intravascular compartment. The tonicity remains unchanged.
The blood volume increases by 20%, from 5,000 mls to 6,000 mls. This is higher than the volume receptor threshold of 7 to 10%.

Selegiline is a monoamine oxidase inhibitor. Inhibition of monoamine oxidase leads to increased levels of norepinephrine and serotonin in the central nervous system.

Pethidine, also known as meperidine, is a strong agonist at the mu and kappa receptors. It inhibits pain neurotransmission and blocks muscarinic-specific actions.

Administering opioid analgesic is relatively contraindicated to individuals taking monoamine oxidase inhibitors. This is because of the high incidence of serotonin syndrome, which is characterized by fever, agitation, tremor, clonus, hyperreflexia and diaphoresis. Onset of symptoms is within hours, and the treatment is mainly through sedation, paralysis, intubation and ventilation.

The clinical findings are more consistent with Serotonin syndrome rather than exacerbation of Parkinson’s. Parkinson’s Disease (PD) exacerbations are defined as patient-reported or caregiver-reported episodes of subacute worsening of PD motor function in 1 or more domains (bradykinesia, tremor, rigidity, or PD-related postural instability/gait disturbance) that caused a decline in functional status, developed over a period of < 2 months, did not fluctuate with medication timing, and are not caused by intentional adjustments of PD medications by the treating neurologist.

Malignant hyperthermia usually occurs within minutes of administration of a volatile anaesthetic, such as halothane, or succinylcholine. There is massive release of calcium from the sarcoplasmic reticulum, leading to fever, acidosis, rhabdomyolysis, trismus, clonus, and hypertension.

In sepsis, it more common for patients to present with hypotension rather than hypertension.

A single chamber pacemaker was implanted in the patient. In VVI mode, a pacemaker paces and senses the ventricle while being inhibited by a perceived ventricular event. The most likely electrical hazard from diathermy is electromagnetic interference (EMI).

EMI has the potential to cause the following: Inhibition of pacing
Asynchronous pacing
Reset to backup mode
Myocardial burns, and
Trigger VF.

Diathermy entails the implementation of high-frequency electrical currents to produce heat and either make incisions or induce coagulation. Monopolar cautery involves disposable cautery pencils and electrosurgical diathermy units. In typical monopolar cautery, an electrical plate is placed on the patient’s skin and acts as an electrode, while the current passes between the instrument and the plate. Monopolar diathermy can therefore interfere with implanted metal devices and pacemaker function.

Bipolar diathermy, where the current passes between the forceps tips and not through the patient and is less likely to generate EMI.

Whilst the presence of a CVP line may in theory predispose the patient to microshock, the use of prerequisite CF electrical equipment makes this very unlikely. The presence of a CVP line and pacemaker does not therefore unduly increase the risk of an electrical hazard.

Isolating transformers are used to protect secondary circuits and individuals from electrical shocks. There is no step-up or step-down voltage (i.e. there is a ratio of 1 to 1 between the primary and secondary windings).

A ground (or earth) wire is normally connected to the metal case of an operating table to protect patients from accidental electrocution. In the event that a fault allows a live wire to make contact with the metal table (broken cable, loose connection etc.) it becomes live. The earth will provide an immediate path for current to safely flow through and so the table remains safe to touch. Being a low resistance path, the earth lets a large current flow through it when the fault occurs ensuring that the fuse or RCD will quickly blow. Without an operating table earth, the patient is not at more risk of an electrical hazard because of the pacemaker.

Atrial natriuretic peptide (ANP) is secreted mainly from myocytes of right atrium and ventricle in response to increased blood volume.
It is secreted by both the right and left atria (right >> left).

It is a 28 amino acid peptide hormone, which acts via cGMP
degraded by endopeptidases.

It serves to promote the excretion of sodium, lowers blood pressure, and antagonise the actions of angiotensin II and aldosterone.

Normally, at rest vagal influence is dominant producing the heart rate of 60-80 beats per minute even if the intrinsic automaticity of Sinoatrial Node is 100-110 beats per minute.

The transplanted heart has no autonomic nervous supply. So, it will respond to endogenous and exogenous catecholamine. This loss of parasympathetic innervation is responsible for the tachycardia in this patient.

Hypokalaemia can cause myocardial excitability and potential for ventricular ectopic and supraventricular arrhythmias. Hypothyroidism is also unlikely to cause tachycardia in this patient.

Nitric oxide (NO), an endothelial-derived relaxant factor (EDRF), is a powerful vasodilator. Its cell-signalling molecule is calcium-dependant and generated endogenous by nitric oxide synthetases from the precursor L-arginine, oxygen and NADPH. Three main isoforms have been isolated and they are inducible (iNO), neuronal (nNO) and endothelial (eNO).

Endothelial NO stimulates intracellular guanylyl cyclase which generates cyclic GMP (cGMP) from its action on guanylyl tri-phosphate (GTP). The cGMP goes on to activate protein kinase G (PKG). PKG phosphorylates cell membrane proteins that regulate intracellular calcium concentrations and level of calcium sensitisation.

Smooth muscle vasodilatation results from:

1. Light chain phosphatase activation.
2. Inhibition of calcium entry into the cell (reducing Ca2+ concentrations) and
3. Hyperpolarisation of cells by activation of H+ channels.

The deep inguinal ring is the entrance of the inguinal canal. It is an opening in the transversalis fascia around 1 cm above the inguinal ligament. Therefore, the superolateral wall is made by the transervalis fascia.

The inferior epigastric vessels run medially to the deep inguinal ring forming its inferomedial border.

The inguinal canal extends obliquely from the deep inguinal ring to the superficial inguinal ring.
An indirect inguinal hernia arises through the deep inguinal ring lateral to the inferior epigastric vessels.

Monoamine oxidase (MOA) enzymes are responsible for the catalyses of monoamine oxidative deamination. It assists the degradation of serotonin, norepinephrine (NE) and dopamine.

They are found in the mitochondria of most central and peripheral nerve tissues.

There are 2 different types:

Type A: Whose main function it to inactivate dopamine, tyramine, norepinephrine and 5-hydroxytryptamine. In addition to the nervous system, it is also found in the liver, brain gastrointestinal tract, pulmonary endothelium and placenta
Type B: Whose main function is to inactivate dopamine, tyramine, tryptamine and phenylethylamine. In addition to the nervous system, it is also found in the liver, brain (especially in the basal ganglia) and blood platelets.

Observers may subconsciously measure or report data in a way that favours the expected study outcome. Therefore, by blinding the study we can eliminate expectation bias.

Recall bias is a systematic error that occurs when the study participants omit details or do not remember previous events or experiences accurately.

Verification can occur during investigations when there is a difference in testing strategy between groups of individuals, which might lead to biasness due to differing ways of verifying the disease of interest.

Nonresponse bias is the bias that occurs when the people who respond to a survey differ significantly from the people who do not respond to the survey.

A distortion that modifies an association between an exposure and an outcome because a factor is independently associated with the exposure and the outcome. Randomization is the best way to reduce the risk of confounding.

There are different classes of electrical equipment that can be classified in the table below:

Class 1 – provides basic protection only. It must be connected to earth and insulated from the mains supply

Class II – provides double insulation for all equipment. It does not require an earth.

Class III – uses safety extra low voltage (SELV) which does not exceed 24 V AC. There is no risk of gross electrocution but risk of microshock exists.

Type B – All of above with low leakage currents (0.5mA for Class IB, 0.1 mA for Class IIB)

Type BF – Same as with other equipment but has ‘floating circuit’ which means that the equipment applied to patient is isolated from all its other parts.

Type CF – Class I or II equipment with ‘floating circuits’ that is considered to be safe for direct connection with the heart. There are extremely low leakage currents (0.05mA for Class I CF and 0.01mA for Class II CF).

Opioid receptors are a large family of seven transmembrane domain receptors. They are of four types:

1) Delta opioid receptor
2) Mu opioid receptor
3) Kappa opioid receptor
4) Orphan receptor-like 1

They contain about 372-400 amino acids and thus their molecular weight is different.

Opioid receptor activation reduces the intracellular cAMP formation and opens K+ channels (mainly through µ and δ receptors) or suppresses voltage-gated N-type Ca2+ channels (mainly κ receptor). These actions result in neuronal hyperpolarization and reduced availability of intracellular Ca2+ which results in decreased neurotransmitter release by cerebral, spinal, and myenteric neurons (e.g. glutamate from primary nociceptive afferents).
However, other mechanisms and second messengers may also be involved, particularly in the long-term

The total body water content of a 70kg man is (70 × 0.6) = 42 litres. For a woman, the calculation is (70 × 0.55) = 38.5 litres.

For a man, it is subdivided into:

Extracellular fluid (ECF) = 14L (1/3)
Intracellular fluid (ICF) = 28L (2/3).

The ECF volume is further divided into:

Interstitial fluid = 10.5 litres
Plasma = 3 litres
Transcellular fluid (CSF/synovial fluid) = 0.5 litres.

Directly measured fluid compartments:

Heavy water (deuterium) can be used to measure total body water content, which is freely distributed.
Albumin labelled with a radioactive isotope or using a dye called Evans blue can be used to measure Plasma volume . They do not diffuse into red blood cells.
Radiolabelled (Cr-51) red blood cells can be used to measure total erythrocyte volume.
Inulin as the tracer can be used to measure ECF volume as it circulate freely in the interstitial and plasma volumes.

Indirectly measured fluid compartments:

Total blood volume can be calculated with the level of haematocrit and the volume of total circulating red blood cells.
ICF volume can be calculated by subtracting ECF volume from total blood volume.

The mandibular branch of the trigeminal nerve passes through the foramen ovale. Other structures that pass through this foramen are the accessory meningeal artery, and occasionally, the lesser petrosal nerve.

These are the structures that pass through the other openings in the cranial fossa:

Foramen rotundum – Maxillary branch of the trigeminal nerve

Foramen lacerum – Greater petrosal nerve, traversed by the internal carotid artery

Superior orbital fissure – Oculomotor nerve; trochlear nerve; lacrimal, frontal and nasociliary branches of the ophthalmic branch of the trigeminal nerve; abducens nerve, superior ophthalmic vein

Stylomastoid foramen – facial nerve.

When there is a fall in ionised plasma calcium levels, the chief cells of the parathyroid glands are stimulated to secrete parathyroid hormone (PTH).

50% of extracellular calcium occurs as non-ionised, protein- (albumin-)bound calcium.

The degree of ionisation increases with low ph and decreases with high pH.

There is increased renal calcium excretion with secretion of calcitonin.

Cardiac output = stroke volume x heart rate

Left ventricular ejection fraction = (stroke volume / end diastolic LV volume ) x 100%

Stroke volume = end diastolic LV volume – end systolic LV volume

Pulse pressure = Systolic Pressure – Diastolic Pressure

Systemic vascular resistance = mean arterial pressure / cardiac output
Factors that increase pulse pressure include:
-a less compliant aorta (this tends to occur with advancing age)
-increased stroke volume

Central cord syndrome is the most commonly occurring type of partial spinal cord lesion. It is more likely to occur in older patients with cervical spondylosis and a hyperextension injury. The injury to the spinal cord occurs in the grey matter causing the following symptoms:

Disproportionally higher motor function weakness in the upper limbs than in lower limbs
Dysfunction of the bladder
Degrees of sensory loss below the level of the lesion

An anterior spinal artery infarction will interrupt the corticospinal tract resulting in paralysis of motor function, loss of pain and temperature sensation, all occurring below the level of the injury.

Brown-Sequard syndrome occurs as a result of the hemisection of the spinal cord. Its symptoms include ipsilateral upper motor neurone paralysis and loss of proprioception, with contralateral loss of pain and temperature sensation.

Spinal cord infarctions rarely occur in the posterior spinal artery.

Cauda equina syndrome occurs as a result of compression of the lumbosacral spinal nerve roots below the level of the conus medullaris. Injury to these nerves will cause partial or complete loss of movement and sensation in this distribution.

Barbituric acid is the barbiturates’ pharmacologically inactive precursor. A pyrimidine heterocyclic nucleus is formed by the condensation of urea and malonic acid. Its pharmacological activity can be influenced by minor structural changes (structure function relationship).

The duration of action and potency as a sedative are influenced by the length of the side chains at C5. Barbiturates with three carbon atoms in their chain last longer than those with two. Anticonvulsant properties are enhanced by branched chains.

The addition of a methyl group at N1 causes a faster onset/offset of action, but it also causes excitatory phenomena (twitching/lower convulsive threshold).

The addition of oxygen and sulphur to C2 increases the molecule’s lipid solubility and thus its potency. Thiopentone (thiobarbiturate) has sulphur groups at C2, making it 20-200 times more lipid soluble than oxybarbiturates.

Microshock refers to ventricular fibrillation caused by miniscule amounts of currents or voltages (100-150 microamperes) passing through the myocardial tissue from external cables arising from electrical components within the cardiac muscle, for example, pacemaker electrodes or saline filled venous catheters.
The risk of shock changes with the construction of electrical equipment in question. The main classes of electrical equipment include: I: Appliances have a protective earth connected to an outer casing which prevents live elements from coming in contact with conductive elements. A fault in this equipment class will result in live elements coming in contact with the outer casing and allowing electrical flow into the protective earth. This triggers the protective fuse to disconnect the electric supply to the appliance.
II: These appliances have reinforced insulation. In the event of a fault which causes the first layer of insulation to fail, the second layer is able to prevent contact of live elements with outer casing.
III: These appliances have no insulation to provide safety, and rely solely on the use of separated extra low voltage source (SELV) which limits voltage to 25V AC or 60V DC allowing for a person to come in contact with it without risk of a shock under normal dry conditions. Under wet conditions, voltage supply should be lowered to reduce risk of shock. These devices have no risk of macroshocks, but some risk of microshocks.
Class I and II electrical appliances are further divided into subtypes developed to limit current leakage in the event of a singular fault:
B (body): Upper limit of current leakage is 500 µA. This current can cause skin tingling and microshocks, but is not sufficient to cause injury.
BF (body floating): These appliances have an isolating capacitor or transformer which separate the secondary circuit from the protective earth. The upper limit of current leakage is the same as type B.
CF (cardiac floating): Upper limit of leakage current during a singular fault is 50 microamps. It is least likely to result in a microshock.

Entonox is a gas that consists of 50% oxygen and 50% Nitrous oxide. Nitrous oxide is sometimes used for anaesthetics but in this combination, it works as a short-acting painkiller.

Under normal working conditions, it exists only in gaseous form in a cylinder. The gauge pressure of a full Entonox cylinder is 137 bar.

Entonox cylinders should be stored horizontally at a temperature above 100 C

Pseudocritical temperature and pseudocritical pressure can be defined as the molal average critical temperature and pressure of mixture components. In other words, the pseudo-critical temperature is the temperature at which the two gases separate. The pseudo-critical temperature of Entonox is approximately -5.50 C

Serum specific IgE assays against allergen sources/molecules are the most commonly used in vitro diagnostic approach. The measurement of specific IgE recognizing allergenic epitopes can be achieved both through the usage of single reagents (singleplex) or with a pre-defined panel of a number of molecules to be tested simultaneously (multiplex).

Several clinical entities have been described and those occurring immediately after drug exposure are immunoglobulin E (IgE)-mediated and explored by skin testing and by the in vitro measurement of serum-specific IgE. The sensitivity of these tests is not 100% and even for patients with a clear positive history, a drug provocation test may be required in order to confirm the diagnosis. The advantages of the in vitro determination of specific IgE antibodies when compared with in vivo testing are that the former poses no direct risk to the patient and does not require personnel with expertise. Even though in vitro tests are recommended in immediate hypersensitivity reactions, their exact place in the diagnostic procedure is not clear and certain authors do not use this method in daily practice. In one study, in terms of sensitivity, 11 of 26 patients (42%) with negative skin tests and a positive drug provocation challenge (or repeated clinical history) had specific IgE to benzylpenicilloyl or amoxicilloyl (4). The specificity of the test was 95€“100%. Therefore, IgE measurements can avoid a potentially harmful drug provocation test.

An elevated serum tryptase does not differentiate between type 1 and type 2 hypersensitivity reaction. It indicates mast cell degranulation.

RAST is a useful aid to improve the overall diagnosis of drug allergies by using radioactive detection. This, however, is now rarely used.

Quantification of basophil activation by CD63 expression can be done by flow cytometry, which forms the basis of experimental drug-induced basophil stimulation tests.

There are different models of flowmeters determined by the applied pressure and its orifice. For instance, the watersight flowmeter functions through applying variable pressure, and it has a variable orifice. In contrast, the bubble flowmeter is operated using a constant pressure and orifice. Flowmeters such as rotameters, Heidbrink and Peak have a constant pressure but variable orifice. On the other hand, flowmeters including a simple pressure gauge, water depression, and pneumotachograph have a constant orifice but variable pressure.

The posterior pituitary is made up mostly of neural tissue. It is responsible for the storage and release of 2 hormones:
– antidiuretic hormone (ADH)
– oxytocin.

These two hormones are synthesised in the supraoptic and paraventricular nuclei of the hypothalamus.

Bulky, greasy stools are associated with improper digestion that can be expected if the pancreas loses its exocrine function. This is common in long-term chronic pancreatitis but since this is the patient’s first presentation with such symptoms, this complication is unlikely.

Peripheral neuropathy is a common complication of chronic diabetes but has been reported with cases of chronic pancreatitis too.

Abdominal distention with shifting dullness is a classic symptom of underlying ascites. Ascites is a complication of many diseases but it is not common with the acute first-time presentation of pancreatitis.

Option E: This points towards abdominal obstruction but in the absence of the more common symptoms, nausea and bilious vomiting, this is unlikely.

Option A: Grey Turner’s sign is the pooling of blood in the retroperitoneal space between the last rib and the top of the hip. The pancreas is a retroperitoneal organ and inflammation of the pancreas can cause retroperitoneal haemorrhage. The sign takes 24-48 hours to develop and can predict a severe attack of acute pancreatitis. The patient has presented with acute pancreatitis due to his history of high alcohol intake, and acute on chronic is unlikely as this is his first presentation. He also has low blood pressure and an increased heart rate, which suggest blood loss with acute pancreatitis.

Haemorrhage, including intracranial bleeding, is a common and potentially fatal side effect of warfarin therapy, and reversing anticoagulation quickly and completely can save lives. When complete and immediate correction of the coagulation defect is required in orally anticoagulated patients with life-threatening haemorrhage, clotting factor concentrates are the only viable option.

For rapid reversal of vitamin K anticoagulants, prothrombin complex concentrates (PCC) are recommended. They contain the vitamin K-dependent clotting factors II, VII, IX, and X and are derived from human plasma. They can be used as an adjunctive therapy in patients with major bleeding because they normalise vitamin K dependent clotting factors and restore haemostasis.

The most common treatments are fresh frozen plasma (FFP) and vitamin K. The efficacy of this approach is questioned due to the variable content of vitamin K-dependent clotting factors in FFP and the effects of dilution. Significant intravascular volume challenge, as well as the possibility of rare complications like transfusion-associated lung injury or blood-borne infection, are all potential issues.

To avoid anaphylactic reactions, vitamin K should be given as a slow intravenous infusion over 30 minutes. Regardless of the route of administration, the reversal of INRs with vitamin K can take up to 24 hours to reach its maximum effect.

Reversal of anticoagulation in patients with warfarin-associated intracranial haemorrhage may be considered with factor VIIa (recombinant), but its use is controversial. There are concerns about thromboembolic events following treatment, as well as questions about assessing efficacy in changes in the INR. If the drug is to be administered, patients should be screened for an increased risk of thrombosis before the drug is given.

A pulse oximeter is a piece of medical equipment used as a non-invasive method of measuring the oxygen saturation of blood.

It works by measuring the ratio of absorption of red and infrared light in a section of blood flow, as red light is largely absorbed by deoxygenated blood, and infrared light is largely absorbed by oxygenated blood.

Pulse oximetry relies on photoplethysmography (PPG) waveforms. The oximeter has 2 sides, with different functions. One side houses light-emitting diodes which are responsible for transmitting 2 light wavelengths, 660nm for red light and 940nm for near infrared light. The other side is a photodetector. The light emitted travels through the body and the amount that is not absorbed is measured by the photodetector.

Smokers often have increased levels of carboxy haemoglobin (COHb). This leads to artificial increases in pulse oximeter readings as it is unable to differentiate between COHb and oxyhaemoglobin (O2HB) as they both absorb red light at 660nm. Every 1% increase of circulating carboxyhaemoglobin, results in a correlative 1% increase in oximeter readings.

Prilocaine toxicity will cause an artificial decrease in oximeter readings. This is because prilocaine metabolites cause methemoglobinemia (MetHB), which are dysfunctional haemoglobins unable to properly transport oxygen. In this case, a laboratory multiwavelength co-oximeter is recommended for a more accurate reading.

Anaemia will not affect oximeter readings as long as haemoglobins in the blood are normal.

Sickle cell disease does not affect oximeter readings despite its ability to cause hypoxia and shift the oxygen dissociation curve to the right.

Brown-red fingernail polish will cause an underestimation of pulse oximeter readings.

The cricoid cartilage is a hyaline cartilage ring surrounding the trachea. It provides support for key phonation muscles.

The inferior border of the cricoid cartilage is attached to the thyroid cartilage and the inferior border is attached to the first tracheal ring through the cricotracheal ligament.

Application of pressure to the cricoid cartilage to reduce risk of aspiration of gastric contents (Sellick manoeuvre) does not stop tracheal aspiration and cannot stop regurgitation into the oesophagus.

A force of 44 newtons to the cricoid cartilage is needed to control regurgitation.

With regards to the autonomic nervous system (ANS)

1. It is not under voluntary control
2. It uses reflex pathways and different to the somatic nervous system.
3. The hypothalamus is the central point of integration of the ANS. However, the gut can coordinate some secretions and information from the baroreceptors which are processed in the medulla.

With regards to the central nervous system (CNS)
1. There are myelinated preganglionic fibres which lead to the
ganglion where the nerve cell bodies of the non-myelinated post ganglionic nerves are organised.
2. From the ganglion, the post ganglionic nerves then lead on to the innervated organ.

Most organs are under control of both systems although one system normally predominates.

The nerves of the sympathetic nervous system (SNS) originate from the lateral horns of the spinal cord, pass into the anterior primary rami and then pass via the white rami communicates into the ganglia from T1-L2.

There are short pre-ganglionic and long post ganglionic fibres.
Pre-ganglionic synapses use acetylcholine (ACh) as a neurotransmitter on nicotinic receptors.
Post ganglionic synapses uses adrenoceptors with norepinephrine / epinephrine as the neurotransmitter.
However, in sweat glands, piloerector muscles and few blood vessels, ACh is still used as a neurotransmitter with nicotinic receptors.

The ganglia form the sympathetic trunk – this is a collection of nerves that begin at the base of the skull and travel 2-3 cm lateral to the vertebrae, extending to the coccyx.

There are cervical, thoracic, lumbar and sacral ganglia and visceral sympathetic innervation is by cardiac, coeliac and hypogastric plexi.

Juxta glomerular apparatus, piloerector muscles and adipose tissue are all organs under sole sympathetic control.

The PNS has a craniosacral outflow. It causes reduced arousal and cardiovascular stimulation and increases visceral activity.

The cranial outflow consists of
1. The oculomotor nerve (CN III) to the eye via the ciliary ganglion,
2. Facial nerve (CN VII) to the submandibular, sublingual and lacrimal glands via the pterygopalatine and submandibular ganglions
3. Glossopharyngeal (CN IX) to lungs, larynx and tracheobronchial tree via otic ganglion
4. The vagus nerve (CN X), the largest contributor and carries ¾ of fibres covering innervation of the heart, lungs, larynx, tracheobronchial tree parotid gland and proximal gut to the splenic flexure, liver and pancreas

The sacral outflow (S2 to S4) innervates the bladder, distal gut and genitalia.

The PNS has long preganglionic and short post ganglionic fibres.
Preganglionic synapses, like in the SNS, use ACh as the neuro transmitter with nicotinic receptors.
Post ganglionic synapses also use ACh as the neurotransmitter but have muscarinic receptors.

Different types of these muscarinic receptors are present in different organs:
There are:
M1 = pupillary constriction, gastric acid secretion stimulation
M2 = inhibition of cardiac stimulation
M3 = visceral vasodilation, coronary artery constriction, increased secretions in salivary, lacrimal glands and pancreas
M4 = brain and adrenal medulla
M5 = brain

The lacrimal glands are solely under parasympathetic control.

Coronary perfusion pressure(CPP), the difference between aortic diastolic pressure (Pdiastolic) and the left ventricular end-diastolic pressure (LVEDP), is mainly determined by the formula:

CPP = Pdiastolic -LVEDP
where
Pdiastolic is the lowest pressure in the aorta before left ventricular ejection and
LVEDP is measured directly during a cardiac catheterisation or indirectly using a pulmonary artery catheter. The pulmonary artery occlusion or wedge pressure approximates best with LVEDP.

Using this patient’s haemodynamic data:

CPP = Pdiastolic – MPAWP
COO = 70 – 12 = 58mmHg.

The Tare weight of a cylinder is the weight when it is empty. So,

Weight of cylinder – tare weight = weight of remaining N2O (g).
4.44 kg – 4 kg = 0.44 kg
Here,
0.44 kg of nitrous oxide remains in the cylinder

Since the molecular weight of nitrous oxide is 44 g and one mole of an ideal gas will occupy a volume of 22.4 litres at STP
Therefore amount left in the cylinder is several (gN2O/44) x 22.4 litres of N2O.

(440/44) x 22.4 = 224 litres.

The structures that pass through the foramen magnum are:

Meningeal lymphatics
Spinal cord
Spinal meninges
Sympathetic plexus of vertebral arteries
Vertebral arteries
Vertebral artery spinal branches
The spinal roots of the accessory nerve.

The jugular foramen contains the vagus nerve, the accessory nerve and glossopharyngeal nerve.

The vertebral veins does not pass into the skull.

In the Child-Pugh classification system, the following 5 components are determined or calculated in order:

Ascites

Grade of encephalopathy

Serum bilirubin (μmol/L)

Serum Albumin (g/L)

Prothrombin time or INR

Raised liver enzymes are not the component of the classification system.

Decreased platelet concentrations with eclampsia were described as early as 1922 by Stancke. The platelet count is routinely measured in women with any form of gestational hypertension. The frequency and intensity of thrombocytopenia vary and are dependent on the severity and duration of the preeclampsia syndrome and the frequency with which platelet counts are performed.

Overt thrombocytopenia defined by a platelet count < 100,000/microliter - indicates severe disease. In general, the lower the platelet count, the higher the rates of maternal and fetal morbidity and mortality. In most cases, delivery is advisable because thrombocytopenia usually continues to worsen. After delivery, the platelet count may continue to decline for the first day or so. It then usually increases progressively to reach a normal level within 3-5 days. In some instances with HELLP syndrome, the platelet count continues to fall after delivery. If these do not reach a nadir until 48 to 72 hours, then preeclampsia syndrome may be incorrectly attributed to one of the thrombotic microangiopathies. The following are other severe features associated with preeclampsia: Proteinuria: >/= 300 mg/24 hours; or urine protein: creatinine ratio >/= 0.3; or dipstick 1+

Renal insufficiency: serum creatinine > 1.1 mg/dL or doubling of creatinine in the absence of other renal disease

Impaired liver function: two times elevated AST/ALT or unexplained right upper quadrant pain or epigastric pain unresponsive to medications

Pulmonary oedema

Cerebral or visual symptoms: headache, visual disturbances.

A Wrights Respirometer measures the volume of air exhaled over the course of one minute of normal breathing

It is unidirectional and measures tidal volume and minute volume of gas flow in one direction. It is placed at the expiratory side (lower pressure than inspiratory side therefore lower chances of gas leaks)

Slits are arranged such that incoming gas will rotate the vane at a rate of 150 revolutions per litre of flowing gas

The Wright respirometer tends to over-read at high flow rates and under-read at low flows because of mechanical causes like friction and inertia and the accumulation of water vapour

The ideal flow for accurate readings is 2 L/min for the respirometer. The respirometer reads the tidal volume and minute volume with a ±5€“10% accuracy within the range of 4€“24 L/min.

The degree of correlation is summarised by the correlation coefficient (r). This indicates how closely the points lie to a line drawn through the plotted data. In parametric data this is called Pearson’s correlation coefficient and can take any value between -1 to +1. A correlation of -1.0 indicates a perfect negative correlation, and a correlation of 1.0 indicates a perfect positive correlation.

For example

r = 1 – strong positive correlation (e.g. systolic blood pressure always increases with age)

r = 0 – no correlation (e.g. there is no correlation between systolic blood pressure and age)

r = – 1 – strong negative correlation (e.g. systolic blood pressure always decreases with age)

Whilst correlation coefficients give information about how one variable may increase or decrease as another variable increases they do not give information about how much the variable will change. They also do not provide information on cause and effect.

In contrast to the correlation coefficient, linear regression may be used to predict how much one variable changes when a second variable is changed.

Each kidney is composed of about 1.2 million uriniferous tubules. Each tubule consists of two parts that are embryologically distinct from each other. They are as follows:
a) Excretory part, called the nephron, which elaborates urine
b) Collecting part which begins as a junctional tubule from the distal convoluted tubule.

There are two types of nephrons in the kidney:
The cortical nephron comprises 80% of the total nephron and its major function is the excretion of waste products in urine whereas the juxtamedullary nephron comprises 20% of the total nephron and its major function is the concentration of urine by counter current mechanism.
In the superficial (cortical) nephrons, peritubular capillaries branch off the efferent arterioles and deliver nutrients to epithelial cells as well as serve as a blood supply for reabsorption and secretion. In juxtamedullary nephrons, the peritubular capillaries have a specialization called the vasa recta, which are long, hairpin-shaped blood vessels that follow the same course as a loop of Henle. The vasa recta serve as osmotic exchangers for the production of concentrated urine.

The kidney receives about 25% of cardiac output and about 20% of this is filtered at the glomeruli of the kidney. Thus, renal blood flow is 1200 ml/minute and renal plasma flow is 650 ml/minute.

Maintenance therapy aims to replace water and electrolytes lost under ordinary conditions. In the perioperative period, maintenance fluid administration may not sufficiently account for the increased fluid requirements caused by third-space losses into the interstitium and gut. Specific recommendations vary with the patient, the procedure, and the type and amount of fluid administered during the operation. The fluid for maintenance therapy replaces deficits arising primarily from insensible losses and urinary or gastrointestinal (GI) losses.

The maintenance fluid volume can be computed using the Holliday-Segar method.

Body weight Fluid volume
first 10 kg 4 ml/kg/hr
next 10-20 kg 2 ml/kg/hr
>20 kg 1 ml/kg/hr

In the past few years, there has been growing recognition of the increased risk of hyponatremia in hospitalized children in intensive care and postoperative settings who receive hypotonic maintenance fluids. Several studies, including a randomized controlled trial and a Cochrane analysis, found that the use of isotonic fluids is associated with fewer electrolyte derangements and concluded that isotonic maintenance fluids are preferable to hypotonic solutions in hospitalized children.

A European consensus statement suggests that an intraoperative fluid should have an osmolarity close to the physiologic range in children in order to avoid hyponatremia, an addition of 1-2.5% in order to avoid hypoglycaemia, lipolysis or hyperglycaemia and should also include metabolic anions as bicarbonate precursors to prevent hyperchloremic acidosis.

A rate of 40 ml/hr is suboptimal.

If 0.9% NaCl with 0% glucose is given at a rate of 65 ml/hr, despite of the correct infusion rate, large volumes can lead to hyperchloremic acidosis.

If 0.18% NaCl with 4% glucose is given at a rate of 65 ml/hr, infusion of this fluid regimen can lead to hyponatremia because of its hypotonicity.

A post-tetanic count of 5 denotes a deep neuromuscular blockade.

Post tetanic count (PTC) is a well-established method of evaluating neuromuscular recovery during intense neuromuscular blockade. It cam ne used when there is no response to single twitch, tetanic, or train-of-four (TOF) stimulation to assess the intensity of neuromuscular blockade and to estimate the duration after which the first twitch in the TOF (T1) is likely to reappear.

During a nondepolarizing block, the high frequency of tetanic stimulation will induce a transient increase in the amount of acetylcholine released from the presynaptic nerve ending, such that the intensity of subsequent muscle contractions will be increased (potentiated) briefly (period of post-tetanic potentiation, which may last 2 to 5€‰min. The neuromuscular response to stimulation during post tetanic potentiation can be used to gauge the depth of block when TOF stimulation otherwise evokes no responses. The number of post tetanic responses is inversely proportional to the depth of block: fewer post tetanic contractions denote a deeper block. When the post tetanic count (PTC) is 6 to 8, recovery to TOF count = 1 is likely imminent from an intermediate-duration blocking agent; when the PTC is 0, the depth of block is profound, and no additional NMBA should be administered.

Dabigatran template is a prodrug and its active metabolite is a direct thrombin inhibitor. It is a synthetic, reversible, non-peptide thrombin inhibitor. This inhibition of thrombin results in a decrease of fibrin and reduces platelet aggregation.

Drugs like warfarin act by inhibiting the activation of vitamin K-dependent clotting factors. These factors are synthesized by the liver and activated by gamma-carboxylation of glutamate residues with the help of vitamin K. Hydroquinone form of vitamin K is converted to epoxide form in this reaction and regeneration of hydroquinone form by enzyme vitamin K epoxide reductase (VKOR) is required for this activity. Oral anticoagulants prevent this regeneration by inhibiting VKOR, thus vitamin K-dependent factors are not activated. These factors include clotting factors II, VII, IX, and X as well as anti-clotting proteins, protein C and protein S.

Bupivacaine is used to decrease feeling in a specific area. It is injected around a nerve that supplies the area, or into the spinal canal’s epidural space.

The maximum volume of 0.5% bupivacaine that should be administered to a 10kg child is 5 ml

Perioperative and postoperative analgesia can both be provided by an inguinal hernia field block. The Iliohypogastric and ilioinguinal nerves, as well as the skin, superficial fascia, and deeper structures, must be blocked for maximum effectiveness. The local anaesthetic should ideally have a long duration of action, be highly concentrated, and have a volume of at least 30 mL.

Plain bupivacaine has a maximum safe dose of 2 mg/kg body weight.

Because the patient weighs 75 kg, 150 mg bupivacaine can be safely administered. Both 30 mL 0.5 percent bupivacaine (150 mg) and 60 mL 0.25 percent bupivacaine (150 mg) are acceptable doses, but 30 mL 0.5 percent bupivacaine represents the optimal volume and strength, potentially providing a denser and longer block.

The maximum safe dose of plain lidocaine has been estimated to be between 3.5 and 5 mg/kg. The patient weighs 75 kg and can receive a maximum of 375 mg using the higher dosage regimen:

There are 200 mg of lidocaine in 10 mL of 2% lidocaine (and therefore 11 mL contains 220 mg)
200 mg of lidocaine is contained in 20 mL of 1% lidocaine.

While alternatives are available, Although the doses of 11 mL lidocaine 2% and 20 mL lidocaine 1% are well within the dose limit, the volumes used are insufficient for effective field block for this surgery.

With 1 in 200,000 epinephrine, the maximum safe dose of lidocaine is 7 mg/kg. The patient can be given 525 mg in this case. Even with epinephrine, 60 mL of 1% lidocaine is 600 mg, which could be considered an overdose.

Calcium is a very important ion and is involved in:
-cell homeostasis
-coagulation
-muscle contraction
-neuronal impulse transmission/membrane stabilization
-bone formation and skeletal strength
-secretion processes

99% is found in bone and 1% in the plasma. Of the 1% that is in the plasma
-45% is free ionized calcium
-45% is bound to proteins, mainly Albumin
-10% is present as an anion complex

Reduced levels of IONIZED calcium give rise to features of hypocalcaemia , resulting in increased excitability of membranes. This results when the total calcium concentration goes below 2 mmol/L.

Features of mild to moderate hypocalcaemia are:
-paraesthesia (peri-oral, fingers)
-tetany
-spasm
-muscle cramps
-ECG changes (prolonged QT)
-Trousseau’s sign (inflation of tourniquet induces carpopedal spasm)
-Chvostek’s sign (tapping the facial nerve – cranial nerve VII – causes facial muscle twitch/spasm)

Features of severe hypocalcaemia are:
-cardiogenic shock and congestive cardiac failure due to reduced myocardial contractility
respiratory distress due to bronchospasm, agitation, confusion, seizures

Features of hypercalcaemia (remember ‘bones, stones, groans and psychic moans’):
-Abdominal pain
-Vomiting
-Constipation
-Polyuria
-Polydipsia
-Depression
-Lethargy
-Anorexia
-Weight loss
-Hypertension
-Confusion
-Pyrexia
-Calcification in the cornea
-Renal stones
-Renal failure
-Decreased Q-T interval
-Cardiac shock/collapse

Phase 0 trials assist the scientists in studying the behaviour of drugs in humans by micro dosing patients. They are used to speed up the developmental process. They have no measurable therapeutic effect and efficiency.

Phase 1 is associated with assessing whether a drug is safe to use or not. The process is extensive and can take up to several months. It also involves healthy participants (less than 100) that are paid to take part in the study. The side effects upon increasing dosage are also addressed by the study. The effects the drug has on humans including how its absorbed, metabolized and excreted are studied. Approximately 70% of the drugs pass this phase.

Phase 2 trials involve patients that are suffering from the disease under study and are associated with determining the efficiency and the optimum dosage of the drug.

Phase 3 also assesses the efficacy but at a higher scale with larger population sample.

Phase 4 trials are involved with the long term effects and side effects of the drug.

Spirometry measures the total volume of air that can be forced out in one maximum breath, that is the total lung capacity (TLC), to maximal expiration, that is the residual volume (RV).

It is conducted using a spirometer which is capable of measuring lung volumes using techniques of dilution.

During spirometry, the following measurements can be determined:
Forced vital capacity (FVC)/vital capacity (VC): The maximum volume of air exhaled in one single forced breathe.
Forced expiratory volume in one second (FEV1)
FEV1/FVC ratio
Peak expiratory flow (PEF): the maximum amount of air flow exhaled in one blow.
Forced expiratory flow (mid expiratory flow): the flow at 25%, 50% and 75% of FVC
Inspiratory vital capacity (IVC): The maximum volume of air inhaled after a full total expiration.

Anatomical dead space is measured using a single breath nitrogen washout called the Fowler’s method.

Residual volume and total lung capacity are both measured using the body plethysmograph or helium dilution

The functional residual capacity is usually measured using a nitrogen washout or the helium dilution technique.

The toxicity of organophosphorus (OP) nerve agents is manifested through irreversible inhibition of acetylcholinesterase (AChE) at the cholinergic synapses, which stops nerve signal transmission, resulting in a cholinergic crisis and eventually death of the poisoned person. Oxime compounds used in nerve agent antidote regimen reactivate nerve agent-inhibited AChE and halt the development of this cholinergic crisis.

Endotoxins are the lipopolysaccharides found in the outer cell wall of Gram-negative bacteria. They are responsible for providing the structure and stability of the cell wall.

They cannot be destroyed by normal sterilisation as they are heat stable molecules. They require the use of certain sterilant such as superoxide, peroxide and hypochlorite to be neutralised.

They stimulate strong immune responses, but can only be destroyed partially by specific antibodies. Repeat infections occur as memory T cells cannot be formed.

It can cause septicaemia and associated symptoms such as fever, shock, hypotension and nausea.

It activates the alternative complement pathway and the coagulation pathway using secreted cytokines.

It is not involved in botulism as clostridium botulinum, the responsible organism, secretes a neurotoxic exotoxin.

Penicillinase is a narrow spectrum β-lactamase that opens the β-lactam ring and inactivates Penicillin G and some closely related congeners. The majority of Staphylococci and some strains of gonococci, B. subtilis, E. coli, and a few other bacteria produce penicillinase.

N. meningitidis is sensitive to penicillin and less than 20% resistance is found in pseudomonas.

The inferior phrenic nerves are at the highest risk of damage as they are the first branches of the abdominal aorta. The potential space at the level of the diaphragmatic hiatus is a potentially useful site for aortic occlusion. However, leaving the clamp applied for more than 10 -15 minutes usually leads to poor outcomes.

The superior phrenic artery branches from the thoracic aorta.

The abdominal aorta begins at the level of the body of T12 near the midline, as a continuation of the thoracic aorta. It descends and bifurcates at the level of L4 into the common iliac arteries.

The branches of the abdominal aorta (with their vertebra level) are:
1. Inferior phrenic arteries: T12 (upper border)
2. Coeliac artery: T12
3. Superior mesenteric artery: L1
4. Middle suprarenal arteries: L1
5. Renal arteries: Between L1 and L2
6. Gonadal arteries: L2 (in males, it is the testicular artery, and in females, the ovarian artery)
7. Inferior mesenteric artery: L3
8. Median sacral artery: L4
9. Lumbar arteries: Between L1 and L4.

The arterial cannula inserted should have parallel walls in order to reduce the risk of interruption of blood flow to distal limbs.

It is essential that the monitor used to display the arterial pressure waves has a frequency capacity of 0.5-40Hz. This is because the pressure waves are a combination of different sine waves of varying frequencies and amplitudes.

The diameter of the catheter is directly proportional to the natural frequency which is the frequency at which the system responsible for monitoring the waves resonates and amplifies the signals. This should be at least ten fold in comparison to the fundamental frequency. The diameter of the catheter is also inversely proportional to the square root of the system compliance, the tubing length and the fluid density within the system.

The presence of an air bubble, a clot or an easily malleable diaphragm and tube can result in wave damping. Increased damping will cause a reduction in the systolic pressure, and an increase in diastolic pressure. The maximum damping value of an appropriate monitoring system would be 0.64.

A rigid, non-malleable diaphragm and tubing can cause a resonance within the system. This resonance will result in an increase in the systolic pressure and a reduction in the diastolic pressure.

The posterior tibial nerve lies on the posterior surface of the tibialis posterior and, lower down the leg, on the posterior surface of the tibia. The nerve accompanies the posterior tibial artery and lies at first on its medial side, then crosses posterior to it, and finally lies on its lateral side. The nerve, with the artery, passes behind the medial malleolus, between the tendons of the flexor digitorum longus and the flexor hallucis longus.

It gives off muscular branches to the soleus, flexor digitorum longus, flexor hallucis longus, and tibialis posterior. A medial calcaneal branches off to supply the skin over the medial surface of the heel, and an articular nerve to supply the ankle joint. Finally, it terminates to become the medial and lateral plantar nerves.

The saphenous nerve is a branch of the femoral nerve that gives off branches that supply the skin on the posteromedial surface of the leg.

The sural nerve is a branch of the tibial nerve that supplies the skin on the lower part of the posterolateral surface of the leg.

The superficial peroneal nerve is one of the terminal branches of the common peroneal nerve. It arises in the substance of the peroneus longus muscle on the lateral side of the neck of the fibular. It ascends between the peroneus longus and brevis muscles, and in the lower part of the leg it becomes cutaneous. Muscular branches of the superficial peroneal nerve supply the peroneus longus and brevis muscles, while medial and lateral cutaneous branches are distributed to the skin on the lower part of the leg and dorsum of the foot. In addition, the cutaneous branches supply the dorsal surfaces of the skin of all the toes, except the adjacent sides of the first and second toes and the lateral side of the little toe.

The superficial peroneal, sural and saphenous nerves cannot be used to assess neuromuscular blocks since they are sensory nerves.

The deep peroneal nerve enters the dorsum of the foot by passing deep to the extensor retinacula on the lateral side of the dorsalis pedis artery. It divides into terminal, medial, and lateral branches. The medial branch supplies the skin of the adjacent sides of the big and second toes. The lateral branch supplies the extensor digitorum brevis muscle. Both terminal branches give articular branches to the joints of the foot. This nerve is too deep to use for neuromuscular blockade assessment.

The epiploic foramen (foramen of Winslow or aditus to the lesser sac) is found behind the free right border of the lesser omentum. A short, 3 cm slit serves as the entrance to the lesser sac from the greater sac.

The epiploic foramen has the following boundaries:
Anteriorly: hepatoduodenal ligament, the bile duct (anteriorly on the right), the hepatic artery (anteriorly on the left), and the portal vein (posteriorly) together with nerves and lymphatics
Superiorly: the peritoneum of the posterior layer of the hepatoduodenal ligament runs over the caudate process of the liver
Posteriorly: inferior vena cava
Floor: upper border of the first part of the duodenum
The anterior and posterior walls of the foramen are normally
apposed, which partly explains why patients can develop large fluid
collections isolated to the greater or lesser sac

Rapid control of the hepatic artery and portal vein can be obtained by compression of the free edge of the lesser omentum (a €˜Pringle’ manoeuvre), which is a potentially useful technique in liver trauma and surgery.

Moderately high doses of dopamine produce a positive inotropic (direct β1 and D1 action + that due to Noradrenaline release), but the little chronotropic effect on the heart.

Vasoconstriction (α1 action) occurs only when large doses are infused.

At doses normally employed, it raises cardiac output and systolic BP with little effect on diastolic BP. It has practically no effect on nonvascular α and β receptors; does not penetrate the blood-brain barrier€”no CNS effects.

Pituitary tumours that compress the optic chiasma primarily affect the neurones that decussate at this location. Bitemporal hemianopia is caused by neurones that emerge from the nasal half of the retina and transmit the temporal half of the visual field.

The axons of ganglion cells in the retina form the optic nerve.

It exits the orbit through the optic foramen and projects to the thalamic lateral geniculate body. The optic chiasma forms above the sella turcica as the nasal fibres decussate along the way. The optic radiation travels from the lateral geniculate body to the occipital cortex.

Lesions at various points along this pathway cause the following visual field defects:

Scotoma implies partial retinal or optic nerve damage.
Monocular vision loss occurs when the optic nerve is completely damaged.
Pathology at the optic chiasma causes bitemporal hemianopia.
Cortical blindness with occipital cortex pathology and homonymous hemianopia with lesions compromising the optic radiation.

Ventricular fibrillation (VT) is an arrhythmia caused by a distortion in the organized contraction of the ventricles leading to an inability to pump blood out into the body.

Amiodarone is an anti arrhythmic drug used for the treatment of ventricular and atrial fibrillations. It is the gold standard of treatment for refractory pulseless ventricular tachycardia (VT) and ventricular fibrillation (VF).

Guidelines for emergency treatment state that only the rescuer carrying out chest compressions on the patient may stand near the defibrillator as it charges.

Cardio-pulmonary resuscitation (CPR) during cardiac arrest is required for 2 minute cycles.

Hypovolaemia is as a cause of pulseless electrical activity (PEA) can be reversed using fluid resuscitation, whereas hypotension during cardiac arrest is either persistent or undetectable and is therefore irreversible.

Hyperkalaemia and hypocalcaemia are treated using calcium salts, but calcium chloride is often preferred over calcium gluconate.

During a pulseless VT or VF, a single precordial thump will be effective if administered within the first seconds of the occurrence of a shockable rhythm.

Mesenteric ischemia is ischemia of the blood vessels of the intestines. It can be life-threatening especially if the small intestine is involved.

A critical factor for survival of acute mesenteric ischemia is early diagnosis and intervention. Angiography uses X-ray and contrast dye to image arteries and identify the severity of ischemia or obstruction.

The celiac axis is the first branch of the abdominal aorta and supplies the entire foregut (mouth to the major duodenal papilla). It arises at the level of vertebra T12. It has three major branches:
1. Left gastric
2. Common hepatic
3. Splenic arteries

There are some important landmarks of vessels at different levels of vertebrae that need to be memorized.

T12 – Coeliac trunk

L1 – Left renal artery

L2 – Testicular or ovarian arteries

L3 – Inferior mesenteric artery

L4 – Bifurcation of the abdominal aorta.

The option that is most responsible is the progressive decrease in venous return of blood to the right atrium. The heart rate does not usually change with PEEP so the fall in cardiac output is due to a reduction in left ventricular (LV) stroke volume (SV).

Note that the interventricular septum does shift toward the left and there is an increased pulmonary vascular resistance (PVR) from overdistention of alveolar air sacs that contribute to the reduction in cardiac output. Any increase in PVR will be associated with reduced pulmonary vascular capacitance.

The important landmarks of vessels arising from the abdominal aorta at different levels of vertebrae are:

T12 – Coeliac trunk

L1 – Left renal artery

L2 – Testicular or ovarian arteries

L3 – Inferior mesenteric artery

L4 – Bifurcation of the abdominal aorta.

Refractometers measure the degree to which the light changes direction, called the angle of refraction. A refractometer takes the refraction angles and correlates them to refractive index (nD) values that have been established. Using these values, you can determine the concentrations of solutions.

The costal elements of the seventh cervical vertebrae form projections known as cervical ribs, which are present in approximately 0.5% – 1 % individuals.

A cervical rib commonly comprises of a head, neck and tubercle. The body of the rib varies from person to person. It extends into the posterior triangle of the neck, where it is either free anteriorly, or attached to the first rib / sternum.

Patients with a cervical rib mostly are asymptomatic and it is usually diagnosed as an incidental finding on chest x-ray. However, in some cases, the subclavian artery and the lower trunk of the brachial plexus are compressed where they pass over the cervical rib. This leads to a condition known as ”neurovascular compression syndrome,” in which these neurovascular structures are compressed between the cervical rib and scalenus anterior.

The most common cause of neurogenic symptoms in approximately 80% of the patients with cervical rib is neck trauma.

In most cases, the tingling, numbness and impaired circulation to the upper limb appears only after puberty. This is because the neck elongates, and the shoulders droop slightly.

Metabolic equivalent (MET) measures the energy expenditure of an individual.

It is calculated mathematically by:

MET = (VO2 max/weight)/3.5 = 21/3.5 = 6 METs

Where 1 MET = 3.5 mL O2/kg/minute is utilized by the body.

Note:

1 MET Eating
Dressing
Use toilet
Walking slowly on level ground at 2-3 mph
2 METs Playing a musical instrument
Walking indoors around house
Light housework
4 METs Climbing a flight of stairs
Walking up hill
Running a short distance
Heavy housework, scrubbing floors, moving heavy furniture
Walking on level ground at 4 mph
Recreational activity, e.g. golf, bowling, dancing, tennis
6 METs Leisurely swimming
Leisurely cycling along the flat (8-10 mph)
8 METs Cycling along the flat (10-14 mph)
Basketball game
10 METs Moderate to hard swimming
Competitive football
Fast cycling (14-16 mph).

The ideal agent for this case should have low blood: gas coefficient, pleasant smell, and high oil: gas coefficient (potent with a low Minimum alveolar coefficient (MAC)). Among the given options, Sevoflurane is perfect with 0.692 blood: gas partition coefficient and is low pungency, and is sweet.

Other drugs with their blood: gas partition coefficient and their smell are given as:
Blood/gas partition coefficient MAC Smell
Enflurane 1.8 1.68 Pungent, ethereal
Desflurane 0.42 7 Pungent, ethereal
Halothane 2.54 0.71 Sweet
Isoflurane 1.4 1.15 Pungent, ethereal

At the ankle joint, midway between the malleoli, the anterior tibial artery changes names, becoming the dorsalis pedis artery (dorsal artery of the foot).

The dorsalis pedis artery is palpated against the underlying tarsals, immediately lateral to the tendon of extensor hallucis longus, from the midpoint between the malleoli to the proximal end of the first intermetatarsal space.

The popliteal artery forms the anterior tibial artery.
The tibioperoneal trunk is a branch of the popliteal artery.
The peroneal artery (also known as the fibular artery) supplies the lateral compartment of the leg.
The external iliac artery is formed from the common iliac artery at the level of the pelvis.

Low molecular weight heparin (LMWH) creates a complex by binding to antithrombin. This complex binds with and inactivates factor Xa.

There is less risk of bleeding with LMWH because it binds less to platelets, endothelium and von Willebrand factor.

LMW binds Xa more readily. The shorter chains are less likely to bind both antithrombin and thrombin.

There is need for monitoring in renal impairment because LMHW is excreted in the urine (and partly by hepatic metabolism)

LMWH have been shown to be as efficacious as unfractionated heparin. It is also safer and have improved inpatient stay and reduced hospital cost.

Hypoxic Pulmonary vasoconstriction (HPV) reflects the constriction of small pulmonary arteries in response to hypoxic alveoli (.i.e.; PO2 below 80-100mmHg or 11-13kPa).

These blood vessels become independent of the nerve stimulus, when blood with a high PO2 flows through the lung which contains a low alveolar PO2.

Thus a low PO2 within the alveoli has been shown to impact on hypoxic pulmonary vasoconstriction (HPV) more than a low PO2 within the blood.

HPV results in the blood flow being directed away from poorly ventilated areas of the lung and helps to reduce the ventilation/perfusion mismatch (not increase).

In animals, volatile anaesthetic agents can diminish HPV, while in adults, the evidence proves less persuading, in spite of the fact that it certainly doesn’t strengthen the effects.

HPV response will be suppressed by 20 parts per million (ppm) of nitric oxide.

ACTH production is stimulated through the secretion of corticotropin-releasing hormone (CRH) from the hypothalamic nuclei.

ACTH secretion has a circadian rhythm. A high level of cortisol in the body stops its production. ACTH is secreted maximally in the morning and concentrations are lowest at midnight.

ACTH can be expressed in the placenta, the pituitary and other tissues.

Conditions where ACTH concentrations rise include: stress, disease and pregnancy.

Glucocorticoids (not mineralocorticoids – aldosterone) switch off ACTH production through a negative feedback loop .

The following terms are used in medical testing:

True negative – The test is negative and the patient does not have the disease.
True positive – The test is positive and the patient has the disease.
False positive – The test is positive but the patient does not have the disease.
False negative – The test is negative but the patient has the disease.

The sensitivity of a predictive test = true positives / (true positives + false negatives).

The specificity of a test = true negatives / (false positives + true negatives).

The negative predictive value of a test = true negatives / (false negatives + true negatives).

Cardiac output = stroke volume x heart rate

Left ventricular ejection fraction = (stroke volume / end diastolic LV volume ) x 100%

Stroke volume = end diastolic LV volume – end systolic LV volume

Pulse pressure = Systolic Pressure – Diastolic Pressure

Systemic vascular resistance = mean arterial pressure / cardiac output
Factors that increase pulse pressure include:
-a less compliant aorta (this tends to occur with advancing age)
-increased stroke volume

Atypical antipsychotic drugs include risperidone and quetiapine. They not only inhibit dopamine receptors in the limbic system, but also histamine (H1) and alpha2 adrenoreceptors. When combined with general and/or central neuraxial block, this might result in severe hypotension.

Donepezil (Aricept) is an acetylcholinesterase (AChE) inhibitor that increases the neurotransmitter acetylcholine in the cerebral cortex and hippocampus in a reversible, non-competitive manner. It is used to reduce the advancement of Alzheimer’s disease symptoms (AD). Rivastigmine and galantamine are two more drugs that work in the same way.

Ginkgo Biloba contains anti-oxidant characteristics and is used to treat early-stage Alzheimer’s disease, vascular dementia, and peripheral vascular disease. It lowers platelet adhesiveness and decreases platelet activating factor (PAF) increasing the risk f bleeding, especially in individuals who are also taking anticoagulants and antiplatelet medication.

Memantine is an antagonist of the NMDA receptor. Synaptic plasticity, which is thought to be a critical component of learning and memory, can be inhibited at high doses. The use of ketamine is a relative contraindication since antagonism of this receptor can cause a dissociative state.

Fractures to the surgical neck of the humerus are common place as it is the weakest point of the proximal humerus bone.

The structures most likely to be damaged are the axillary nerve and the posterior circumflex humeral artery as they surround the surgical neck.

The radial nerve runs along the radial groove, so injury to it would likely occur with a mid-shaft fracture of the humerus.

The brachial artery is most likely to be injured as a result of a supracondylar fracture of the humerus which increases the risk of volkmaan’s ischemic contractures.

Injury to the musculocutaneous nerve is least likely to happen and it very uncommon.

A thermocouple, or a thermal junction, is temperature measuring device consisting of a pair of dissimilar metal (bimetallic) wires or strips joined together. Typically, copper and constantan (an alloy of 55% copper and 45% nickel) are used. When there is contact between these metals, a small voltage is generated in the order of millivolts. The magnitude of the thermojunction electromotive force (emf) is proportional to applied temperature (the Seebeck effect). This physical principle is applied in the measurement of temperature. The electromotive force at the measuring junction is proportional to temperature.

Two wires with different coefficients of expansion, joined together, can be used as a switch for thermostatic control.

Semiconductors are NOT used in thermocouple. The resistance of the measuring junction of a thermocouple is irrelevant.

Its known that 68.3% of the total values of a normally distributed variable are found within a range of 1 standard deviation from the mean which makes the range to be 4.3 to 4.9 mmol/L.

The tibial nerve lies on top of the vessels contained within the inferior aspect of the popliteal fossa.

In the superior aspect of the fossa, the tibial nerve runs lateral to the vessels, before then travelling superficial to the vessels, and then finally changing course to lie medial to the vessels.

The popliteal artery is the most deep structure present in the popliteal fossa.

Type I – immediate hypersensitivity reaction

Examples are: Atopy, urticaria, Anaphylaxis, Asthma( IgE mediated).

Type II – Antibody mediated cytotoxic reaction

Examples are: Autoimmune haemolytic anaemia, Thrombocytopenia( IgM or IgG mediated).

Type III – Immune complex mediated reaction

Examples are: Serum sickness,SLE – IgG., Farmers lungs, rheumatoid arthritis

Type IV – Delayed hypersensitivity reaction

Examples are: Contact dermatitis, drug allergies.

Type V – Autoimmune

Graves’
Myasthenia – IgM or IgG.

The coronary sinus is large venous structure located on the posterior aspect of the left atrium, coursing within the left atrioventricular groove. The function of the coronary sinus is to drain the venous blood from the majority of the heart. It opens into the right atrium between the opening of inferior vena cava, the fossa ovalis and the right atrioventricular orifice. The coronary sinus is often guarded by a thin, semicircular endocardial fold, also known as the thebesian valve.
Tributaries include: Great cardiac vein, middle cardiac vein, small cardiac vein, posterior vein of left ventricle, oblique vein of left atrium. The great cardiac vein is the largest tributary of the coronary sinus.

The pectinate muscles (musculi pectinati) are parallel muscular ridges that extend anterolaterally on the right atrial walls. The most prominent pectinate muscle, which forms the bridge of the sulcus terminalis internally, is the taenia sagittalis (second crest or septum spurium).

In the left atrium, the pectinate muscles are confined to the inner surface of its atrial appendage. They tend to be fewer and smaller than in the right atrium. This is due to the embryological origin of the auricles, which are the true atria.

Pectinate muscles of the atria are different from the trabeculae carneae, which are found on the inner walls of both ventricles.

The interior of the right atrium has five distinct features:
1. Sinus venarum – smooth, thin-walled posterior part of the right atrium where the SVC, IVC, and coronary sinus open
2. Musculi pectinati – a rough anterior wall of pectinate muscles
3. Tricuspid valve orifice – the opening through which the right atrium empties blood into the right ventricle
4. Crista terminalis – separates the rough (musculi pectinati) from the smooth (sinus venarum) internally
5. Fossa ovalis – a thumbprint size depression in the interatrial septum, which is a remnant of the oval foramen and its valve in the foetus.

When the loading dose of Digoxin is given, the primary thing to consider is the volume of distribution. The volume of distribution is the proportionality factor that relates the total amount of drug in the body to the concentration. LD is computed as:

LD = Volume of distribution X (desired plasma concentration/bioavailability)

Digoxin is an anti-arrhythmic drug with a large volume of distribution and high bioavailability, and only a small percentage of Digoxin is bound to plasma proteins (,20%).

In the case, since the arrhythmia is not life-threatening, there is no need for the medication to work rapidly.

Gentamicin is a broad-spectrum antibiotic whose mechanism of action involves inhibition of protein synthesis by binding to 30s ribosomes. Its major adverse effect is nephrotoxicity and ototoxicity

Aminoglycoside bind to 30s subunit of ribosome causing misreading of mRNA

Tetracyclines inhibit protein synthesis through reversible binding to bacterial 30s ribosomal subunits, which prevent binding of new incoming amino acids (aminoacyl-tRNA) and thus interfere with peptide growth.

Chloramphenicol binds to the 50s subunit and inhibits peptidyl transferase

Clindamycin binds to the 50s ribosomal subunit of bacteria and disrupts protein synthesis by interfering with the transpeptidation reaction, which thereby inhibits early chain elongation.

Doxycycline belongs to the family of tetracyclines and inhibits protein synthesis through reversible binding to bacterial 30s ribosomal subunits, which prevent binding of new incoming amino acids (aminoacyl-tRNA) and thus interfere with peptide growth.