A tonsillar sinus or fossa is a space that is bordered by the triangular fold of the palatoglossal and palatopharyngeal arches in the lateral wall of the oral cavity. The palatine tonsils are in these sinuses.

The glossopharyngeal nerve is the main sensory nerve for the tonsillar fossa. The tonsillar branches of the glossopharyngeal nerve supply the palatine tonsils forming a plexus around it. Filaments from this plexus are distributed to the soft palate and fauces where they communicate with the palatine nerves. A lesser contribution is made by the lesser palatine nerve. Because of this otalgia may occur following tonsillectomy.

Prostaglandins do not play a major role in regulating RBF in healthy resting individuals. However, during pathophysiological conditions such as haemorrhage and reduced extracellular fluid volume (ECVF), prostaglandins (PGI2, PGE1, and PGE2) are produced locally within the kidneys and serve to increase RBF without changing GFR. Prostaglandins increase RBF by dampening the vasoconstrictor effects of both sympathetic activation and angiotensin II. These effects are important because they prevent severe and potentially harmful vasoconstriction and renal ischemia. Synthesis of prostaglandins is stimulated by ECVF depletion and stress (e.g. surgery, anaesthesia), angiotensin II, and sympathetic nerves.

Non-steroidal anti-inflammatory drugs (NSAIDs), such as ibuprofen and naproxen, potently inhibit prostaglandin synthesis. Thus administration of these drugs during renal ischemia and hemorrhagic shock is contraindicated because, by blocking the production of prostaglandins, they decrease RBF and increase renal ischemia. Prostaglandins also play an increasingly important role in maintaining RBF and GFR as individuals age. Accordingly, NSAIDs can significantly reduce RBF and GFR in the elderly.

The diaphragm divides the thoracic cavity from the abdominal cavity. Structures penetrate the diaphragm at different vertebral levels through openings in the diaphragm to communicate between the two cavities. The diaphragm has openings at three vertebral levels:

T8: vena cava, terminal branches of the right phrenic nerve
T10: oesophagus, vagal trunks, left anterior phrenic vessels, oesophageal branches of the left gastric vessels
T12: descending aorta, thoracic duct, azygous and hemi-azygous vein.

The standard error of the mean (SEM) is a measure of the spread expected for the mean of the observations – i.e. how ‘accurate’ the calculated sample mean is from the true population mean. The relationship between the standard error of the mean and the standard deviation is such that, for a given sample size, the standard error of the mean equals the standard deviation divided by the square root of the sample size.

SEM = SD / square root (n)

where SD = standard deviation and n = sample size

Automated blood gas analysers are commonly used to analyse blood gas samples, and they measure specific components of the arterial blood gas sample, whether directly or indirectly.

The following are the components of arterial blood gas:

pH = measured (directly determined) acid-base balance of the blood

PaO2 = measured partial pressure of oxygen in arterial blood

PaCO2 = measured partial pressure of carbon dioxide in arterial blood

HCO3 = calculated (indirectly determined) concentration of bicarbonate in arterial blood

Base excess/deficit = calculated relative excess or deficit of base in arterial blood

SaO2 = calculated arterial oxygen saturation unless a co-oximetry is obtained, in which case it is measured

The tracheobronchial tree is subdivided into the conducting and the respiratory zones.

The zones from proximal to distal are:

Trachea
Bronchi
Bronchioles
Terminal bronchioles
Respiratory bronchioles
Alveolar ducts
Alveolar sacs

from the trachea to terminal bronchioles are the conducting zone while the respiratory zone is from the respiratory bronchioles to the alveola sacs.

Thermocouples are based on the Seebeck effect, i.e. a small thermoelectric current is generated when two different metal wires are put into contact at both ends with their junctions having a different temperature. If one junction is open, a contact electromotive force is generated. The current, or the electromotive force, is to a first approximation proportional to the temperature difference ΔT between the two junctions. A better approximation is obtained with a MacLaurin expansion with the second power of ΔT.

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

The resistance at the measuring junction is irrelevant.

The resistance of a thermistor varies exponentially with temperature, while the resistance of a measuring junction varies linearly with temperature. Incorporated into a Wheatstone bridge is this unknown resistance, which is used to indirectly measure temperature.

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

According to European Group protocol for the investigation of MH susceptibility, muscle biopsy should be performed on quadriceps muscle (either vastus medialis or vastus lateralis), using regional anaesthesia (avoiding local anaesthetic infiltration) or general anaesthetic techniques. Local anaesthetic solution within muscle fibres may affect in vitro contraction testing.

Desflurane is a weak triggering anaesthetic of malignant hyperthermia so is avoided in MH susceptible patients. This includes all volatile inhalational agents and suxamethonium.

General anaesthetic with the volatile free anaesthetic machine may be considered but spinal anaesthesia is a better choice due to the possibility of airway problems.

The volume expired in the first second of maximal expiration after a maximal inspiration is known as forced expiratory volume in one second (FEV1), and it indicates how quickly full lungs can be emptied. It is the most commonly measured parameter for bronchoconstriction assessment.

The maximum volume of air exhaled after a maximal inspiration is known as the ‘slow’ vital capacity (VC). VC is normally equal to FVC after a forced vital capacity (FVC) or slow vital capacity (VC) manoeuvre, unless there is an airflow obstruction, in which case VC is usually higher than FVC.

The FEV1/FVC (Tiffeneau index) is a clinically useful index of airflow restriction that can be used to distinguish between restrictive and obstructive respiratory disorders.

The average expired flow over the middle half (25-75 percent) of the FVC manoeuvre is the forced expiratory volume (FEF25-75). The airflow from the resistance bronchioles corresponds to this. It’s a more sensitive indicator of mild small airway narrowing than FEV1, but it’s difficult to tell if the VC (or FVC) is decreasing or increasing.

The maximum expiratory flow rate achieved is called the peak expiratory flow (PEF), which is usually 8-14 L/second.

Normal distribution, also called Gaussian distribution, the most common distribution function for independent, randomly generated variables, and describes the spread for many biological and clinical measurements.

Properties of the Normal distribution

symmetrical i.e. Mean = mode = median

68.3% of values lie within 1 SD of the mean

95.4% of values lie within 2 SD of the mean

99.7% of values lie within 3 SD of the mean

The empirical rule, or the 68-95-99.7 rule, tells you where most of the values lie in a normal distribution: Around 68% of values are within 1 standard deviation of the mean.

Around 95% of values are within 2 standard deviations of the mean. Around 99.7% of values are within 3 standard deviations of the mean.
the standard deviation (SD) is a measure of how much dispersion exists from the mean.

SD = square root (variance)

The empirical rule, or the 68-95-99.7 rule states where most of the values lie in a normal distribution. Around 68% of values fall within 1 S.D of the mean, about 95% within 2 S.D of the mean, and about 99.7% of values within 3 S.D of the mean. Therefore, 95.4% is the most reasonable answer if results are normally distributed.

Phase IIa studies are usually pilot studies designed to demonstrate clinical efficacy or biological activity (‘proof of concept’ studies) whereas phase IIb studies determine the optimal dose at which the drug shows biological activity with minimal side-effects (€˜definite dose-finding’ studies).

Phase III and Phase IV studies are performed on larger set of participants (usually hundreds to thousands) when safety and efficacy have been established.

Such a high rise of end-tidal CO2 (EtCO2) in a patient who is spontaneously breathing is often encountered.

Close observation should occur for further rises in EtCO2 and other signs of malignant hyperthermia. If this were to rise even more, it might be wise to ensure that ventilatory support is available.

A lot would depend on whether surgery was almost completed. At this stage of anaesthesia, it would be inappropriate to administer opioid antagonists or respiratory stimulants.

External carotid artery originates at the upper border of the thyroid cartilage. It ascends and lies anterior to the internal carotid arteries and posterior to the posterior belly of the digastric muscle and stylohyoid muscle.

The external carotid artery has eight important branches:
Anterior surface:
1. Superior thyroid artery (first branch)
2. Lingual artery
3. Facial artery
Medial branch
4. Ascending pharyngeal artery
Posterior branches
5. Occipital artery
6. Posterior auricular artery
Terminal branches
7. Maxillary artery
8. Superficial temporal artery.

When a drug is given via intravenous infusion, the plasma concentration rises exponentially as a wash-in curve until it reaches steady-state concentration (the point at which the infusion rate is balanced by the elimination rate or clearance). To reach this steady state, the drug will take 4-5 half-lives.

Cpss (target plasma concentration at steady state) and clearance (CL) in ml/minute or litre/hour are the two factors that determine the infusion rate or dose (ID) in mg/hour of a drug.

ID = Cpss × CL

We know the infusion rate is 20 ml/hour in this case. The drug’s concentration is 5 mg/mL. The patient is receiving 100 mg of the drug per hour, with a 20 L/hour clearance rate.

ID = Cpss × 20

Therefore,

Cpss = 100 mg/20000 ml

Cpss = 0.005 mg/mL or 5 mcg/mL

The cylindrical structure(spine), starts from the foramen magnum in medulla oblongata at the skull’s base. Its length varies in gender with men having 45cm and women having up to 43 cm. The spine contains 31 pairs of spinal nerves, named according to the spinal region:
– 8 cervical nerve pairs ( C1-C8)
– 12 thoracic nerve pairs ( T1-T12)
– 5 lumbar nerve pairs (L1-L5)
– 5 sacral nerves (S1-S5) and
– 1 coccygeal nerve pair.
These spinal nerves are classified as the peripheral nervous system though they branch from the spinal cord and central nervous system. They interact directly with the spinal cord to modulate the motor and sensory information from the peripheral’s region. As the nerves emerges form the spinal cords they are known as rootlets. They join to form nerve roots, and depending on their position, we have anterior nerve roots and posterior.

The spinal cord is supplied by two posterior and one anterior spinal arteries which anastomoses caudally, at the conus medullaris.

The anterior spinal artery supplies the anterior two-thirds of the spinal cord and medulla. Disruption of the anterior spinal artery supply is characterised by ischaemia or infarction of motor tracts (corticospinal) and loss of pain and temperature sensation below the level of the lesion.

The posterior spinal arteries supply the posterior columns (posterior third of the spinal cord). Infarction of the posterior columns results in the loss of proprioceptive, vibration and two-point discrimination.

The spinal cord normally ends at the level of L1 or L2 in an adult and L3 in a newborn.

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.

With a history of drug abuse, the patient is likely dependent on and tolerant to opioids. He is also likely to experience significant pain from his injuries. Providing adequate pain relief with regular paracetamol and NSAIDs in combination with a pure opioid agonist while at the same time avoiding occurrence of acute withdrawal syndrome is the goal.

Administering a baseline dose of opioid corresponding to the patient’s usual opioid use plus an opioid dose required to address the level of pain the patient experience can help prevent opioid withdrawal. The best approach is by empowering the patient to use patient controlled analgesia (PCA). The infusion rate, bolus dose and lock-out time are adjusted accordingly. Using PCA helps in avoiding staff/patient confrontations about dose and dosing interval.

2.5 mg heroin is equivalent to 3.3 mg morphine. This patient is usually on 200 mg of heroin per 24 hours. The equivalent dose of morphine is 80 × 3.3 =254 mg per 24 hours (11 mg/hour).

Epidural or spinal opioids might be the best choice for providing a systemic dose of opioids when patients are in remission to avoid withdrawal. Lumbar vertebral fractures is a contraindication to this route of analgesia.

The long half life of Oral methadone make titration to response difficult. Also, absorption of methadone by the gastrointestinal tract is variable. It is therefore NOT the best choice for acute pain management.

Drugs cross the placenta by Simple, Ion channel and Facilitated diffusion; Exocytosis and Endocytosis, Osmosis, and Active transport (primary and secondary)

The following factors influence rate of diffusion across the placenta:

Protein binding
Degree of ionisation
Placental blood flow
Maternal and foetal blood pH
Materno-foetal concentration gradient.
Thickness of placental membrane
Molecular weight of drug <600 Daltons cross by diffusion
Lipid solubility (lipid soluble molecules readily diffuse across the placenta)

Rocuronium has a F/M ratios of 0.16, a 30% plasma protein binding, low lipid solubility, a low volume of distribution (0.25L/kg), and a high molecular weight (530Da).

Observation bias occurs when the behaviour of an individual changes that results from their awareness of being observed.

Recall bias introduced when participants in a study are systematically more or less likely to recall and relate information on exposure depending on their outcome status.

Attrition bias is a systematic error caused by unequal loss of participants from a randomized controlled trial (RCT). In clinical trials, participants might dropout due to unsatisfactory treatment or efficacy, intolerable adverse events, or even death.

Selection bias introduced when the individuals are not chosen randomly to take a part in the study. It usually occurs when the research decides who is going to be studied, they are not the representative of the population.

Lead-time bias occurs when a disease is detected by a screening test at an earlier time point rather than it would have been diagnosed by its clinical appearance. In this bias, earlier detection improves the survival time in the intervention group.

The pH at which the drug exists in 50 percent ionised and 50 percent unionised forms is known as the pKa.

To calculate the proportion of ionised to unionised form of an ACID, use the Henderson-Hasselbalch equation.

pH = pKa + log ([A-]/[HA])

or

pH = pKa + log [(salt)/(acid)]
pH = pKa + log ([ionised]/[unionised]).

Hence, if the pKa ˆ’ pH = 0, then 50% of drug is ionised and 50% is unionised.

In this example:

7.4 = 4.3 + log ([ionised]/[unionised])
7.4 ˆ’ 4.3 = log ([ionised]/[unionised])
log 3.1 = log ([ionised]/[unionised])

Simply put, the antilog is the inverse log calculation. In other words, if you know the logarithm of a number, you can use the antilog to find the value of the number. The antilogarithm’s definition is as follows:

y = antilog x = 10x

Antilog to the base 10 of 0 = 1, 1 = 10, 2 =100, 3 = 1000, and 4 = 10,000.

If you want to find the antilogarithm of 3.1, for a number between 3 and 4, the antilogarithm will return a value between 1000 and 10,000. The ratio is 1:1 if pKa = pH, that is, pH pKa = log 0. (50 percent ionised and unionised).

According to the above value, there is only one unionised molecule for every approximately 1000 (1259) ionised molecules of this drug in plasma, implying that this drug is largely ionised in plasma (99.99 percent ).

This scenario describes rebreathing management.

Changes is exhaustion of the soda lime and a progressive rise in circuit deadspace is the most likely explanation for the capnograph.

It is important that the soda lime canister is inspected for a change in colour of the granules. Initially fresh gas flow should be increased and then if necessary, replace the soda lime granules. Other strategies include changing to another circuit or bypassing the soda lime canister after the fresh gas flow is increased.

Any other causes of increased equipment deadspace should be excluded.

Intraoperative hypercarbia can be caused by:

1. Hypoventilation – Breathing spontaneously; drugs which include anaesthetic agents, opioids, residual neuromuscular blockade, pre-existing respiratory or neuromuscular disease and cerebrovascular accident.
2. Controlled ventilation- circuit leaks, disconnection, miscalculation of patient’s minute volume.
3. Rebreathing – Soda lime exhaustion with circle, inadequate fresh gas flow into Mapleson circuits, increased breathing system deadspace.
4. Endogenous source – Tourniquet release, hypermetabolic states (MH or thyroid storm) and release of vascular clamps.
5. Exogenous source – Absorption of CO2 absorption from the pneumoperitoneum.

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.

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

Due to an increased tidal volume with little change or slight increase in respiratory rate, Minute ventilation at term is increased by about 50%. Hypothalamic function are thought to influence by Progesterone, oestradiol and prostaglandins. This causes a mild compensated respiratory alkalosis.

Maternal PaCO2 is usually decreased to about 32 mmHg (4.27 kPa) as a result of this increased alveolar ventilation at term . A compensatory decrease in serum bicarbonate from 27 to 21 mmol/L by renal excretion lessens the impact of maternal alkalosis.

The walls of the anterior nasal passage are supplied by the anterior ethmoidal branch of the nasociliary nerve, and the floor is innervated by the superior dental nerve (not the sphenopalatine nerves).

The walls and floor of the posterior nasal passage are innervated by the long and short sphenopalatine nerves and the great palatine nerve (not the superior dental nerves and the nasociliary nerve).

The vestibule is innervated by small branches of the infraorbital branch of the maxillary nerve.

The nasopharynx is innervated by the sensory branches of the trigeminal nerve (not the great palatine nerve).

Ketamine is usually used as a racemic mixture, i.e. (R/S)-ketamine. For over 20 years, use of the more potent (S)-enantiomer by anaesthesiologists has become a preferred option due to the assumption of increased anaesthetic and analgesic properties, a more suitable control of anaesthesia, and of an improved recovery from anaesthesia.

The use of ketamine in anaesthesia and psychiatry may be accompanied by the manifestation of somatic and especially psychomimetic symptoms such as perceptual disturbances, experiences of dissociation, euphoria, and anxiety.

Noradrenaline also called norepinephrine belongs to the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter.

They have sympathomimetic effects acting via adrenoceptors (α1, α2, β1, β2, β3) or dopamine receptors (D1, D2).

May cause reflex bradycardia, reduce cardiac output and increase myocardial oxygen consumption

Number needed to treat can be defined as the number of patients who need to be treated to prevent one additional bad outcome.

It can be found as:

NNT=1/Absolute Risk Reduction (rounded to the next integer since number of patients can be integer only).

where ARR= (Risk factor associated with the new drug group) — (Risk factor associated with the currently available drug)

So,

ARR= (0.04-0.03)

ARR= 0.01

NNT= 1/0.01

NNT=100

Risk ratio (relative risk) compares the probability of an event in an exposed (experimental) group to that of an event in the unexposed (control) group.

A relative risk of 1 suggests that there is no discernible difference in the outcome whether or not it has been exposed.

A relative risk of less than 1 indicates that probability of occurrence of an event is less if there is exposure.

A relative risk of greater than 1 highlights that an event is most likely to occur if it was provided exposure. Since you believe that exposure (the new drug) would have side effects, the value should be greater than 1.