Variance and standard deviation indicate the dispersion of the plot from mean value and thus are not really helpful in summarizing the mean.

Range is the difference between maximum and minimum value that is 45 in this case.

The mean in this case is 6.2 due to the presence of an outlier 45. In the presence of outlier mean can be misleading as it is quite sensitive to skewness in data.

Mode is the most frequent value. In this case mode has 4 values: 0,1,2,4.

In case of skewedness, median is the most apt representative of the mean as it is not affected by outliers. In this case since the data set has even values i.e. 10. Median is the average of the 5th & 6th entry after arranging the data in ascending order like that in case of the question (0,0,1,1,2,2,3,4,4,45). This turns out to be 2.

When the eye is compressed or the extra-ocular muscles are tractioned, the oculocardiac reflex causes a decrease in heart rate.

The ophthalmic division of the trigeminal nerve provides the afferent limb. This synapses with the vagus nerve’s visceral motor nucleus in the brainstem. The efferent signal is carried by the vagus nerve to the heart, where increased parasympathetic tone reduces sinoatrial node output and slows heart rate.

The most common symptom is sinus bradycardia, but junctional rhythm and asystole can also occur.

The cephalic vein is a superficial vein that runs through the forearm and the arm, before draining into the axillary vein where it terminates.

Patients who have sustained thermal injuries are at high risk of becoming hypercatabolic with larger cardiac outputs and oxygen consumptions.

The hypermetabolic states increase with an increase in the burn severity and surface area of the skin affected. A patient with thermal injuries affecting 60% of the total surface area of the body will have twice the normal metabolic rate.

The optimal temperature for nursing patients with burn injuries is 30°C to conserve the energy usage. The areas affected by the burn injuries should be covered to reduce loss of fluid via evaporation. Resetting hypothalamic thermoregulation will cause a 1-2°C increase in core temperature.

Burn injuries will have an immediate effect on the intestine, destroying the barrier function and allowing for the movement of bacteria and endotoxins within hours.

Enteral nutrition allows for the delivery of nutrients directly to the stomach or intestine. It has correlation with a dampened hypermetabolic response to a thermal and injury, especially when initiated early as it helps to protect the integrity of the mucosal lining and prevents the movement of bacteria into circulation.

Diet changes have been linked to reduced mortality due to burn injuries. Diets high in protein especially (calorie: nitrogen ratio of 100: 1), have the highest correlation with improved survival rates.

Parenteral feeds may be required alongside enteral nutrition, even with the increased risks of infection.

For establishing a cause effect relationship, following criteria must be met:

1. Coherence & Consistency

2. Temporal Precedence

3. Specificity

As can be seen, sensitivity (The probability of a positive test) is not among these deciding factors..

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

An ipsilateral phrenic nerve block will result from a successful interscalene block (ISB).

The phrenic nerve is the diaphragm’s sole motor supply, and ipsilateral hemidiaphragmatic paresis affects up to 100% of patients who receive ISBs. Phrenic nerve palsy is usually well tolerated and goes unnoticed by healthy people. However, forced vital capacity decreases by approximately 25%, which can produce ventilatory compromise in patients with limited pulmonary reserve, requiring assisted ventilation.

Vocal cord palsy occurs when the recurrent laryngeal nerve is inadvertently blocked, causing hoarseness and possibly acute respiratory insufficiency. Unless bilateral laryngeal nerve palsy occurs, which can cause severe laryngeal obstruction, this complication is usually of little consequence.

ISB can also cause cranial nerve X and XII palsy (Tapia’s syndrome). One-sided cord paralysis, aphonia, and the patient’s tongue deviating toward the block’s side are all symptoms.

When a local anaesthetic spreads to the stellate ganglion and its cervical sympathetic nerves, Horner’s syndrome can develop. Ptosis of the eyelid, miosis, and anhidrosis of the face are all symptoms. Horner’s syndrome, on the other hand, may not indicate that the brachial plexus is sufficiently blocked.

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.

With respect to oxygen transport in cells, almost all oxygen is transported within erythrocytes. There is limited solubility and only 1% is carried as solution. Thus, the amount of oxygen transported depends upon haemoglobin concentration and its degree of saturation.

Haemoglobin is a globular protein composed of 4 subunits. Haem is made up of a protoporphyrin ring surrounding an iron atom in its ferrous state. The iron can form two additional bonds – one is with oxygen and the other with a polypeptide chain.
There are two alpha and two beta subunits to this polypeptide chain in an adult and together these form globin. Globin cannot bind oxygen but can bind to CO2 and hydrogen ions.
The beta chains are able to bind to 2,3 diphosphoglycerate. The oxygenation of haemoglobin is a reversible reaction. The molecular shape of haemoglobin is such that binding of one oxygen molecule facilitates the binding of subsequent molecules.

The oxygen dissociation curve (ODC) describes the relationship between the percentage of saturated haemoglobin and partial pressure of oxygen in the blood.
Of note, it is not affected by haemoglobin concentration.

Chronic anaemia causes 2, 3 DPG levels to increase, hence shifting the curve to the right

Haldane effect – Causes the ODC to shift to the left. For a given oxygen tension there is increased saturation of Hb with oxygen i.e. Decreased oxygen delivery to tissues.
This can be caused by:
-HbF, methaemoglobin, carboxyhaemoglobin
-low [H+] (alkali)
-low pCO2
-ow 2,3-DPG
-ow temperature

Bohr effect – causes the ODC to shifts to the right = for given oxygen tension there is reduced saturation of Hb with oxygen i.e. Enhanced oxygen delivery to tissues. This can be caused by:
– raised [H+] (acidic)
– raised pCO2
-raised 2,3-DPG
-raised temperature

Erythromycin binds to the 50s subunit of bacterial rRNA complex and inhibits protein synthesis.

Vancomycin binds to the acyl-D-ala-D-ala portion of the growing cell wall in a susceptible gram-positive bacterium. After binding, it prevents the cell wall from forming the cross-linking.

Trimethoprim binds to dihydrofolate reductase and inhibits the reduction of dihydrofolic acid to tetrahydrofolic acid. Tetrahydrofolic acid is an essential precursor in the thymidine synthesis pathway and interference with this pathway inhibits bacterial DNA synthesis.

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 correct answer is the Purkinje fibres, which conducts at a velocity of about 4m/sec.

The electrical conduction system of the heart starts with the SA node which generates spontaneous action potentials.

This is conducted across both atria by cell to cell conduction, and occurs at around 1 m/s. The only pathway for the action potential to enter the ventricles is through the AV node in a normal heart.
At this site, conduction is very slow at 0.05ms, which allows for the atria to completely contract and fill the ventricles with blood before the ventricles depolarise and contract.

The action potentials are conducted through the Bundle of His from the AV node which then splits into the left and right bundle branches. This conduction is very fast, (,2m/s), and brings the action potential to the Purkinje fibres.

Purkinje fibres are specialised conducting cells which allow for a faster conduction speed of the action potential (,2-4m/s). This allows for a strong synchronized contraction from the ventricle and thus efficient generation of pressure in systole.

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 respiratory quotient is the ratio of CO2 produced to O2 consumed while food is being metabolized:

RQ = CO2 eliminated/O2 consumed

Most energy sources are food containing carbon, hydrogen and oxygen. Examples include fat, carbohydrates, protein, and ethanol. The normal range of respiratory coefficients for organisms in metabolic balance usually ranges from 1.0-0.7.

Granulated sugar is a refined carbohydrate with no significant fat, protein or ethanol content.

The RQ for carbohydrates is = 1.0

The RQ for the rest of the compounds are:

Fats RQ = 0.7
The chemical composition of fats differs from that of carbohydrates in that fats contain considerably fewer oxygen atoms in proportion to atoms of carbon and hydrogen.

Protein RQ = 0.8
Due to the complexity of various ways in which different amino acids can be metabolized, no single RQ can be assigned to the oxidation of protein in the diet; however, 0.8 is a frequently utilized estimate.

The right atrium receives blood supply from the SVC, IVC, and coronary sinus. It forms the right border of the heart.

The interior of the right atrium has 5 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 – an anterior rough, 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

The trabeculae carneae are irregular muscular elevations that form the interior of the right ventricle.

End-tidal carbon dioxide (ETCO2) monitoring has been an important factor in reducing anaesthesia-related mortality and morbidity. Hypercarbia, or hypercapnia, occurs when levels of CO2 in the blood become abnormally high (Paco2 >45 mm Hg). Hypercarbia is confirmed by arterial blood gas analysis. When using capnography to approximate Paco2, remember that the normal arterial–end-tidal carbon dioxide gradient is roughly 5 mm Hg. Hypercarbia, therefore, occurs when PETco2 is greater than 40 mm Hg.

The most likely explanation for the changes in capnograph is either exhaustion of the soda lime and a progressive rise in circuit dead space.

Inspect the soda lime canister for a change in colour of the granules. To overcome soda lime exhaustion, the first step is to increase the fresh gas flow (FGF) (Option A). Then, if need arises, replace the soda lime granules. Other strategies that can work are changing to another circuit or bypassing the soda lime canister, but remember that both these strategies are employed only after increasing FGF first. Exclude other causes of equipment deadspace too.

There are also other causes for hypercarbia to develop intraoperatively:
1. Hypoventilation is the most common cause of hypercapnia. A. Inadequate ventilation can occur with spontaneous breathing due to drugs like anaesthetic agents, opioids, residual NMDs, chronic respiratory or neuromuscular disease, cerebrovascular accident.
B. In controlled ventilation, hypercapnia due to circuit leaks, disconnection or miscalculation of patient’s minute volume.
2. Rebreathing – Soda lime exhaustion with circle, inadequate fresh gas flow into Mapleson circuits and increased breathing system deadspace.
3. Endogenous source – Tourniquet release, hypermetabolic states (MH or thyroid storm) and release of vascular clamps.
4. Exogenous source – Absorption of CO2 from pneumoperitoneum.

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.

Magnesium is a unique calcium antagonist as it can act on most types of calcium channels in vascular smooth muscle and as such would be expected to decrease intracellular calcium. One major effect of decreased intracellular calcium would be inactivation of calmodulin-dependent myosin light chain kinase activity and decreased contraction, causing arterial relaxation that may subsequently lower peripheral and cerebral vascular resistance, relieve vasospasm, and decrease arterial blood pressure.

The vasodilatory effect of MgSO4 has been investigated in a wide variety of vessels. For example, both in vivo and in vitro animal studies have shown that it is a vasodilator of large conduit arteries such as the aorta, as well as smaller resistance vessels including mesenteric, skeletal muscle, uterine, and cerebral arteries.

The theory of cerebrovascular vasospasm as the aetiology of eclampsia seemed to be reinforced by transcranial Doppler (TCD) studies which suggested that MgSO4 treatment caused dilation in the cerebral circulation as well as in animal studies that used large cerebral arteries.

Impaired ventricular relaxation reduces diastolic filling and therefore preload.

Decreased blood volume decreases preload due to reduced venous return.

Heart failure is characterized by reduced ejection fraction and therefore stroke volume.

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 (is increased by stroke volume) = 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
Aortic stenosis would decrease stroke volume as end systolic volume would increase.
This is because of an increase in afterload, an increase in resistance that the heart must pump against due to a hard stenotic valve.

The left subclavian artery originates from the aortic arch, while the right subclavian artery originates from the brachiocephalic artery.

The subclavian artery gives off branches on both sides of the body:
1. Vertebral artery
2. Internal thoracic artery
3. Thyrocervical trunk
4. Costocervical trunk
5. Dorsal scapular artery

The superior thyroid artery is the first branch of the external carotid artery. The other branches of the external carotid artery are:
1. Superior thyroid artery
2. Ascending pharyngeal artery
3. Lingual artery
4. Facial artery
5. Occipital artery
6. Posterior auricular artery
7. Maxillary artery
8. Superficial temporal artery

There are different types of temperature measurement. These include:

Thermistor – this is a type of semiconductor, meaning they have greater resistance than conducting materials, but lower resistance than insulating materials. There are small beads of semiconductor material (e.g. metal oxide) which are incorporated into a Wheatstone bridge circuit. As the temperature increases, the resistance of the bead decreases exponentially

Thermocouple – Two different metals make up a thermocouple. Generally, in the form of two wires twisted, welded, or crimped together. Temperature is sensed by measuring the voltage. A potential difference is created that is proportional to the temperature at the junction (Seebeck effect)

Platinum resistance thermometers (PTR) – uses platinum for determining the temperature. The principle used is that the resistance of platinum changes with the change of temperature. The thermometer measures the temperature over the range of 200°C to1200°C. Resistance in metals show a linear increase with temperature

Tympanic thermometers – uses infrared radiation which is emitted by all living beings. It analyses the intensity and wavelength and then transduces the heat energy into a measurable electrical output

Gauge/dial thermometers – Uses coils of different metals with different co-efficient of expansion. These either tighten or relax with changes in temperature, moving a lever on a calibrated dial.

Krebs’ cycle (tricarboxylic acid cycle or citric acid cycle) is a sequence of reactions to release stored energy through oxidation of acetyl coenzyme A (acetyl-CoA). Some of the products are carbon dioxide and hydrogen atoms.

The sequence of reactions, known collectively as oxidative phosphorylation, only occurs in the mitochondria (not cytoplasm).

The Krebs cycle can only take place when oxygen is present, though it does not require oxygen directly, because it relies on the by-products from the electron transport chain, which requires oxygen. It is therefore considered an aerobic process. It is the common pathway for the oxidation of carbohydrate, fat and some amino acids, required for the formation of adenosine triphosphate (ATP).

Pyruvate enters the mitochondria and is converted into acetyl-CoA. Acetyl-CoA is then condensed with oxaloacetate, to form citrate which is a six carbon molecule. Citrate is subsequently converted into isocitrate, alpha-ketoglutarate, succinyl-CoA, succinate, fumarate, malate and finally oxaloacetate.

The only five carbon molecule in the cycle is Alpha-ketoglutarate.

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.

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

The bifurcation of the abdominal aorta into common iliac arteries occurs at the level of L4. The bifurcation is a common site for atherosclerotic plaques as it is an area of high turbulence.

Leriche Syndrome is an aortoiliac occlusive disease and affects the distal abdominal aorta, iliac arteries, and femoropopliteal vessels. It has a triad of symptoms:
1. Claudication (cramping lower extremities pain that is reproducible by exercise)
2. Impotence (reduced penile arterial flow)
3. Absent/weak femoral pulses (hallmark)

T12 – aorta enters the diaphragm with the thoracic duct and azygous veins

L2 – testicular or ovarian arteries branch off the aorta

L3 – inferior mesenteric artery

With regards to compensatory response to blood loss, the following sequence of events take place:

1. Decrease in venous return, right atrial pressure and cardiac output
2. Baroreceptor reflexes (carotid sinus and aortic arch) are immediately activated
3. There is decreased afferent input to the cardiovascular centre in medulla. This inhibits parasympathetic reflexes and increases sympathetic response
4. This results in an increased cardiac output and increased SVR by direct sympathetic stimulation. There is increased circulating catecholamines and local tissue mediators (adenosine, potassium, NO2)
5. Fluid moves into the intravascular space as a result of decreased capillary hydrostatic pressure absorbing interstitial fluid.

A slower response is mounted by the hypothalamus-pituitary-adrenal axis.
6. Reduced renal blood flow is sensed by the intra renal baroreceptors and this stimulates release of renin by the juxta-glomerular apparatus.
7. There is cleavage of circulating Angiotensinogen to Angiotensin I, which is converted to Angiotensin II in the lungs (by Angiotensin Converting Enzyme ACE)

Angiotensin II is a powerful vasoconstrictor that sets off other endocrine pathways.
8. The adrenal cortex releases Aldosterone
9. There is antidiuretic hormone release from posterior pituitary (also in response to hypovolaemia being sensed by atrial stretch receptors)
10. This leads to sodium and water retention in the distal convoluted renal tubule to conserve fluid
Fluid conservation is also aided by an increased amount of cortisol which is secreted in response to the increase in circulating catecholamines and sympathetic stimulation.

The spinous process is the part of a vertebrae that is directed posteriorly.

Typical cervical vertebra have spinous processes that are small and bifid, except for C7, which has a long and prominent spinous process.

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.

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 superficial inguinal ring is an opening in the aponeurosis of the external oblique muscle, just above and lateral to the pubic crest.

The superficial ring resembles a triangle more than a ring with the base lying on the pubic crest and its apex pointing towards the anterior superior iliac spine. The sides of the triangle are crura of the opening in the external oblique aponeurosis. The lateral crura of the triangle is attached to the pubic tubercle. The medial crura of the triangle is attached to the pubic crest.

The external oblique aponeurosis forms the anterior wall of the inguinal canal and also the lateral edge of the superficial inguinal ring. The rectus abdominis lies posteromedially, and the transversalis posterior to this.