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.

The basilar artery is a large vessel that is formed by the union of the vertebral arteries at the junction of the medulla and pons. It lies in the pontine cistern and follows a shallow groove on the ventral pontine surface, extending to the upper border of the pons.

The basilar artery then bifurcates into the two posterior cerebral arteries that form part of the Circle of Willis.

Classification of hemorrhagic shock according to Advanced Trauma Life Support is as follows:

– Class I haemorrhage (blood loss up to 15%) in which there is no change in blood pressure, RR, or pulse pressure.

– Class II haemorrhage (15-30% blood volume loss) where there is tachycardia, tachypnoea, and a decrease in pulse pressure.

– Class III haemorrhage (30-40% blood volume loss) where clinical signs of inadequate perfusion, marked tachycardia, tachypnoea, significant changes in mental state, and measurable fall in systolic pressure is seen. It almost always requires a blood transfusion.

– Class IV haemorrhage (> 40% blood volume loss) in which marked tachycardia, significant depression in systolic pressure and very narrow pulse pressure, and markedly depressed mental state with cold and pale skin are seen.

Loss of >50% results in loss of consciousness, pulse, and blood pressure.

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.

Since the data is normally distributed, 95% of the values lie with in the interval 70 to 90. This can be calculated as follows:

Interval= Mean ± ( 2 times standard deviation)
= 80 ± 2(5)
= 80 ± 10
= 70 & 90

The rest of the 5% are distributed symmetrically beyond 90 and below 70 which means 2.5% of the values lie above 90.

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.

The inferior mesenteric artery arises from the abdominal aorta at the level of the L3 vertebrae and supplies blood to the final third of the transverse colon, the descending colon, the sigmoid colon and the uppermost part of the rectum.

It is the artery most likely to affect the left colon.

Rifampicin is a derivative of a rifamycin (other derivatives are rifabutin and rifapentine). It is bactericidal against both dividing and non-dividing mycobacterium and acts by inhibiting DNA-dependent RNA polymerase. Thus this drug inhibits RNA synthesis.

The deep inguinal ring lies approximately 1.5-2cm above the midpoint of the inguinal ligament, the halfway point between the anterior superior iliac spine and the pubic tubercle, next to the epigastric vessels.

It is an important point in determining the nature of an inguinal hernia (direct or indirect). The patient is asked to cough after the hernia is reduced, with pressure applied to the deep inguinal ring. The hernia reappearing indicates it is direct, moving through the posterior wall of the inguinal canal.

Inferior and lateral to the pubic tubercle is the normal anatomical position of the neck of a femoral hernia.

Superior and medial to the pubic tubercle is the site of the superficial inguinal ring, and the normal anatomical position of the neck of an inguinal hernia.

The mid-inguinal point is located halways between the pubic symphysis and the anterior superior iliac spine. It is the surface marking for taking the femoral pulse.

The action of class 1 anti-arrhythmic is sodium channel blockade. Subclasses of this action reflect effects on the action potential duration (APD) and the kinetics of sodium channel blockade.

Drugs with class 1A prolong the APD and refractory period, and dissociate from the channel with intermediate kinetics.

Drugs with class 1B action shorten the APD in some tissues of the heart, shorten the refractory period, and dissociate from the channel with rapid kinetics.

Drugs with class 1C action have minimal effects on the APD and the refractory period, and dissociate from the channel with slow kinetics.

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).

This patient is morbidly obese and has a high risk of developing hypoxia. This will be exacerbated by the patient’s supine position, as a result of:

Functional residual capacity has been reduced (FRC)
Increased closing capacity (CC)
Reduced tidal volume due to increased airway resistance, decreased thoracic cage compliance, and decreased respiratory muscle strength and endurance
Following induction of general anaesthesia, there is a tendency for atelectasis and increased O2 consumption due to the increased workload of respiratory muscles and the overall increase in metabolism.

Pre-oxygenation with 100 percent oxygen via a tight-fitting mask can be done using either tidal volume breaths for three to five minutes or four vital capacity breaths in normal circumstances. In the head-up position, this patient is much more likely to be adequately pre-oxygenated, maximising the FRC and minimising the CC. In spontaneously breathing patients, the Mapleson A and circle systems are both effective, but the Mapleson D requires 160-200 ml/kg/minute to prevent rebreathing.

During normal tissue metabolism, there is production of CO2 (acid) which is then expired by the lungs. If metabolism switches from aerobic to anaerobic due to a lack of oxygen, the tissues are unable to completely oxidise sugars to CO2. As a consequence, the sugars can only be partially oxidised to lactic acid. Since lactic acid cannot be expired by the lungs, it remains in the circulation leading to metabolic acidosis.

Also, normal tissue metabolism leads to the production of some amount of acid from the breakdown of proteins. These acids are excreted from the body by kidney filtration. Renal failure will therefore results in acidosis after several days.

An increased acidosis stimulates the brain’s respiratory centres to increase the respiratory rate. This lowers the CO2 in the blood, leading to a decrease in its acidity. Renal excretion removes the excess acid, resulting in a normal pH, and a reduced PaCO2 and HCO3.

pH PaCO2 (kPa) HCO3
Compensated respiratory acidosis 7.34 7.2 29
Acute respiratory acidosis 7.25 7.3 22
Compensated metabolic acidosis 7.34 3.6 14
Metabolic acidosis 7.21 5.3 15
Metabolic alkalosis 7.51 5.1 30

The gag reflex is a protective mechanism that prevents any foreign material to enter the aerodigestive tract.

This reflex has afferent (sensory) and effect (motor) components.
– Glossopharyngeal nerve form the afferent limb
– Vagus nerve form the efferent limb.

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.

An agonist is a molecule with intrinsic efficacy and affinity for a receptor. The ability of a drug-receptor interaction to produce a maximal response is referred to as intrinsic efficacy or activity. Efficacy also refers to a drug’s ability to have a therapeutic or beneficial effect. Although the potencies of morphine and fentanyl differ, they both have the same intrinsic efficacy.

The amount of drug required to produce a given effect is referred to as potency. If drug X is effective in a dose of 100 mcg, its potency is greater than if drug Y is effective in a dose of 10 mg.

The therapeutic index, also known as the margin of safety, is a ratio of the lethal or serious side effect dose of a drug divided by the therapeutic dose of the same drug.

The term bioavailability refers to the ability of a substance to be absorbed. The area under a curve (AUC) of a graphic plot of plasma concentration and time is used to calculate oral bioavailability. It’s used to figure out how much of a drug to take and when to take it.

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

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.

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

The correct answer is the mean, median and mode of normally distributed data are the same value. This is as a result of the bell shaped curve which is equal on both sides.

The bell-shape indicates that values around the mean are more frequent in occurrence than the values farther away.

In a normal distribution:
1) +/- one standard deviation of the mean accounts for 68% of the data.
2) +/- two standard deviations of the mean accounts for 95% of the data.
3) +/- three standard deviations of the mean accounts for 99.7% of the data.

Oxygen delivery depends on 2 variables.
1) Content of oxygen in blood
2) Cardiac output

Oxygen content (arterial) = (Hb (g/dL) x 1.39 x SaO2 (%) ) + (0.023 x PaO2 (kPa))

Oxygen content (mixed venous) = (Hb (g/dL) x 1.39 x mixed venous saturation) + (0.023 x mixed venous partial pressure of oxygen in kPA)

Huffner’s constant = 1.39 = 1g of Hb binds to 1.39 ml of O2

Oxygen delivery DO2 (ml/min) = 10 x Cardiac output (L/min) x Oxygen content
Normally 1000ml/min

Oxygen consumption VO2 (ml/min) = 10 x Cardiac output (L/min) x Difference in arterial and mixed venous oxygen content
Normally 250 ml/min

Oxygen extraction ratio (OER) = VO2/DO2
Normally approximately 25%

A person remaining at high altitudes for days, weeks, or years becomes more and more acclimatized to the low PO2, so it causes fewer deleterious effects on the body.

After acclimatization, it becomes possible for the person to work harder without hypoxic effects or to ascend to still higher altitudes. The principal means by which acclimatization comes about are (1) a great increase in pulmonary ventilation, (2) increased numbers of red blood cells, (3) diffusing capacity of the lungs, (4) increased vascularity of the peripheral tissues, and (5) increased ability of the tissue cells to use oxygen despite low PO2.

The cardiac output often increases as much as 30% immediately after a person ascends to high altitude but then decreases back toward normal over a period of weeks as the blood haematocrit increases, so the amount of oxygen transported to the peripheral body tissues remains about normal.

The first line of treatment in case of hypotension is fluid resuscitation.

Activated charcoal can be used within one hour of tricyclic antidepressant ingestion but an intact and secure airway must be checked before intervention. The risk of aspiration should be assessed.

Vasopressors are indicated for the treatment of hypotension following (Tricyclic Antidepressant) TCA overdose when patients fail to respond to fluids and bicarbonate.

The α-2 adrenoceptor has three subtypes (2a, 2b and 2c). The receptors are generally presynaptic, meaning they prevent noradrenaline from being released at nerve endings. Both the central and peripheral nerve systems are affected by the α-2 agonists. α-2 agonists cause drowsiness, analgesia, and euphoria centrally in the locus coeruleus (in the brainstem), lower the MAC of volatile anaesthetic drugs, and are used to treat acute withdrawal symptoms in chronic opioid addicts.

The most common impact of α-2 agonists on heart rate is bradycardia. The adrenoreceptors α-1 and α-2 are blocked by phenoxybenzamine.

Clonidine is a selective agonist for the α -2 receptor, having a 200:1 affinity ratio for the α-2: α-1 receptors, respectively.

Tizanidine is similar to clonidine but has a few key variances. It has the same sedative, anxiolytic, and analgesic characteristics as clonidine, although for a shorter period of time and with less effect on heart rate and blood pressure.

Dexmedetomidine, like clonidine, is a highly selective α-2 adrenoreceptor agonist having a higher affinity for the α-2 receptor. In the case of α-2: α-1 receptors, the affinity ratio is 1620:1. It has a biphasic blood pressure impact and induces a brief rise in blood pressure and reflex bradycardia (activation of α-2b subtypes of receptors in vascular smooth muscles), followed by a reduction in sympathetic outflow from the brainstem and hypotension/bradycardia.

A prodrug is methyldopa. It blocks the enzyme dopa-decarboxylase, which converts L-dopa to dopamine (a precursor of noradrenaline and adrenaline). It is also converted to alpha-methyl noradrenaline, a centrally active agonist of the α-2 adrenoreceptor. These two processes contribute to its blood pressure-lowering effect. Without a rise in heart rate, cardiac output is generally maintained. The heart rate of certain patients is slowed.

Phentolamine is a short-acting antagonist of peripheral α-1 and α-2 receptors that causes peripheral vascular resistance to reduce and vasodilation to increase. It’s used to treat hypertensive situations that aren’t life threatening (e.g. hypertension from phaeochromocytoma).

A baroreceptor reflex commonly causes reflex tachycardia when systemic vascular resistance drops.

After ingestion of more than 150 mg/kg paracetamol within 24 hours, hepatotoxicity can occur but can also develop rarely after ingestion of doses as low as 75 mg/kg within 24 hours. Hepatocellular damage will not occur in this patient and therefore no need to engage management pathway for paracetamol overdose. If his weight was <33 kg or he already had a history of impaired liver function, then the management would bde different.

Subsequent post-operative doses will be a standard dose of 1 g 6 hourly.

This is a drug administration error and should be reported as an incident even though the patient will not be harmed.

The answer is anterior to the spermatic cord.

The inguinal canal in men contains the ilioinguinal nerve, the genitofemoral nerve and the spermatic cord.

The ilioinguinal nerve arises of the L1 nerve root with the Iliohypogastric nerve, before entering the inguinal canal from the side, through the muscles of the abdomen, travelling superficial to the spermatic cord.

The inferior vena cava is formed by the union of the right and left common iliac veins. The inferior vena cava has no functional valves like the one-way valves commonly found in many veins. The forward flow to the heart is driven by the differential pressure created by normal respiration.

The absence of functional valves has an important clinical role when cannulating during cardiopulmonary bypass.

There is a valve that is non-functioning called the eustachian valve that lies at the junction of the IVC and the right atrium. This valve has a role to help direct the flow of oxygen-rich blood through the right atrium to the left atrium via the foramen ovale during fetal life. It has no specific function in adult life.

Cardiac conduction

Phase 0 – Rapid depolarization. Opening of fast sodium channels with large influx of sodium

Phase 1 – Rapid partial depolarization. Opening of potassium channels and efflux of potassium ions. Sodium channels close and influx of sodium ions stop

Phase 2 – Plateau phase with large influx of calcium ions. Offsets action of potassium channels. The absolute refractory period

Phase 3 – Repolarization due to potassium efflux after calcium channels close. Relative refractory period

Phase 4 – Repolarization continues as sodium/potassium pump restores the ionic gradient by pumping out 3 sodium ions in exchange for 2 potassium ions coming into the cell. Relative refractory period

The needle should be inserted just below the skin at the mid inguinal point which is the surface indicator for the femoral artery.

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.