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.

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.

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.

According to the Safe Anaesthesia Liaison Group, the most important factor to consider the cannula access, and if the patient is properly receiving the total intravenous anaesthesia. The cannula access must be regularly checked for kinks, leaks and disconnections.

Below are the safety precautions and policies to be followed for total intravenous anaesthesia among children and adults:

When administering TIVA, a non-return valve must be used on any intravenous fluid line;
When using equipment, it is essential that clinical staff know its limitations and uses;
Sites of intravenous infusions should be visible so they may be monitored for disconnection, leaks or perivenous infusion into the subcutaneous tissues; and,
Organisations must give preference to clearly labelled intravenous connectors and valves.

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.

Hydrochloric acid is lost when you vomit for a long time (HCl). As a result, the following can be expected, in varying degrees of severity:

Hypokalaemia
Hypochloraemia
Increased bicarbonate to compensate for chloride loss and metabolic alkalosis

The alkalosis causes potassium to move from the intracellular to the extracellular compartment at first. Long-term vomiting and dehydration cause potassium to be excreted by the kidneys in order to conserve sodium. Dehydration can cause urea and creatinine levels to rise.

The actual base excess is always greater than the standard base excess.

The actual base excess (BE) is a measurement of a base’s contribution to a blood gas picture’s metabolic component. It’s the amount of base that needs to be added to a blood sample to bring the pH back to 7.4 after the respiratory component of a blood gas picture has been corrected (PaCO2 of 40 mmHg or 5.3 kPa). The BE has a normal range of +2 to 2. A large positive BE indicates a severe metabolic alkalosis, while a large negative BE indicates a severe metabolic acidosis. As a result, the actual BE in vitro is unaffected by CO2.

In vivo, however, standard BE is not independent of pCO2 because blood with haemoglobin acts as a better buffer than total ECF.

As a result, it is impossible to tell the difference between compensating for a respiratory disorder and compensating for the presence of a primary metabolic disorder.

The differences between in vitro and in vivo behaviour can be mostly eliminated if the BE is calculated for a haemoglobin concentration of 50 g/L (the ‘effective’ or virtual value of Hb if it was distributed throughout the extracellular space) rather than the actual haemoglobin. Because haemoglobin has a lower buffering capacity, the standard BE is higher than the actual BE. It reflects the BE better in the extracellular space rather than just the intravascular compartment.

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.

The femoral triangle is a wedge-shaped area found within the superomedial aspect of the anterior thigh. It is a passageway for structures to leave and enter the anterior thigh.

Superior: Inguinal ligament
Medial: Adductor longus
Lateral: Sartorius
Floor: Iliopsoas, adductor longus and pectineus

The contents include: (medial to lateral)
Femoral vein
Femoral artery-pulse palpated at the mid inguinal point
Femoral nerve
Deep and superficial inguinal lymph nodes
Lateral cutaneous nerve
Great saphenous vein
Femoral branch of the genitofemoral nerve

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.

Prednisolone 5 mg is the same as 20 mg hydrocortisone.

Prednisolone 40 mg is the same as 8 x 20 mg or 160 mg of prednisolone.

Mineralocorticoid effects and variations in action duration are not taken into account in these comparisons.

5 mg of prednisolone is the same as Dexamethasone 750 mcg, Hydrocortisone 20 mg, Methylprednisolone 4 mg, and Cortisone acetate 25 mg.

The body of the Entonox cylinder is usually blue (occasionally white), with blue and white shoulders. Entonox contains a 50:50 mixture of oxygen and nitrous oxide, with a full cylinder pressure of 13700 KPa (137 bar). The cylinder is equipped with a two-stage pressure regulator for safe operation.

The cylinder body and shoulder of nitrous oxide are (French) blue.

In today’s anaesthetic workstations, carbon dioxide cylinders are no longer used.

The body of an oxygen cylinder is black, with a white shoulder.

The white Heliox (21 percent oxygen and 79 percent helium) cylinder has a brown and white shoulder. The administration of this gas mixture, which is less dense than air, is used to reduce turbulence (stridor) of inspiratory flow in patients with upper airway obstruction.

Even though aprotinin reduces fibrinolysis and therefore bleeding, there is an associated increased risk of death. It was withdrawn in 2007.
Protein C is dependent upon vitamin K and this may paradoxically increase the risk of thrombosis during the early phases of warfarin treatment.

The coagulation cascade include two pathways which lead to fibrin formation:
1. Intrinsic pathway – these components are already present in the blood
Minor role in clotting
Subendothelial damage e.g. collagen
Formation of the primary complex on collagen by high-molecular-weight kininogen (HMWK), prekallikrein, and Factor 12
Prekallikrein is converted to kallikrein and Factor 12 becomes activated
Factor 12 activates Factor 11
Factor 11 activates Factor 9, which with its co-factor Factor 8a form the tenase complex which activates Factor 10

2. Extrinsic pathway – needs tissue factor that is released by damaged tissue)
In tissue damage:
Factor 7 binds to Tissue factor – this complex activates Factor 9
Activated Factor 9 works with Factor 8 to activate Factor 10

3. Common pathway
Activated Factor 10 causes the conversion of prothrombin to thrombin and this hydrolyses fibrinogen peptide bonds to form fibrin. It also activates factor 8 to form links between fibrin molecules.

4. Fibrinolysis
Plasminogen is converted to plasmin to facilitate clot resorption

The rima glottidis is a narrow, triangle-shaped opening between the true vocal cords.

The vocal folds (true vocal cords) control sound production. The apex of each fold projects medially into the laryngeal cavity.

Each vocal fold includes these vocal ligaments:

Vocalis muscle (most medial part of thyroarytenoid muscle)

The glottis is composed of the vocal folds, processes and rima glottidis.

The rima glottidis is the narrowest potential site within the larynx, as the vocal cords may be completely opposed, forming a complete barrier.

In the neonatal stage, the tongue is usually large and comes to the normal size at the age of 1 year. The vocal cords lie inverse C4 and as it reaches the grown-up position inverse C5/6 by the age of 4 (not 1 year).

Due to the immature cricoid cartilage, the larynx lies more anterior in newborn children. That’s why the cricoid ring is the narrowest part of the paediatric respiratory tract, while in the adults the tightest portion of the respiratory route is vocal cords. The epiglottis is generally expansive and slants at a point of 45 degrees to the laryngeal opening.

The carina is the ridge of the cartilage in the trachea at the level of T2 in newborn (T4 in adults), that separates the openings of right and left main bronchi.

Neonates have a comparatively low number of alveoli and then this number gradually increases to a most extreme by the age of 8 (not 3 years).

Neonates are obligatory nose breathers and any hindrance can cause respiratory issues (e.g., choanal atresia).

Body fluid compartments in a 70kg male:
Total volume=42L (60% body weight)
Intracellular fluid compartment (ICF) =28L
Extracellular fluid compartment (ECF) = 14L

ECF comprises:
Intravascular fluid (plasma) = 3L
Extravascular fluid = 11L

Extravascular fluids comprises:
Interstitial fluid = 10.5L
Transcellular fluid = 0.5L

ANOVA is based upon within group variance (i.e. the variance of the mean of a sample) and between group variance (i.e. the variance between means of different samples). The test works by finding out the ratio of the two variances mentioned above. (Commonly known as F statistic).

Bupivacaine is used to decrease sensation 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

Cardiopulmonary exercise testing (CPX, CPEX, CPET) is a non-invasive testing method used to determine the performance of the heart, lungs and skeletal muscle. It measures the exercise tolerance of the patient.

The parameters measured include:

ECG and ST-segment analysis and blood pressure
Oxygen consumption (VO2)
Carbon dioxide production (VCO2)
Gas flows and volumes
Respiratory exchange ratio (RER)
Respiratory rate
Anaerobic threshold (AT)

The anaerobic threshold (AT) is an estimate of exercise ability. Any measurement below 11 ml/kg/min is usually related with an increase in mortality, especially when there is a background of myocardial ischaemia occurring during the test.

Peak VO2 <20 mL/kg with a low AT have a correlation with postoperative complications and a 30 day mortality. The CPX test is used for risk-testing patients prior to surgery to determine the appropriate postoperative care facilities. The V slope measured in CPX testing represents VO2 versus VCO2 relationship. During AT, the ramp of V slope increases, but does not provide a picture of postoperative mortality.

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.
2. Left Anterior Descending (LAD) artery – supplies the front and bottom of the left ventricle and front of the interventricular septum

The left anterior descending coronary artery is the largest coronary artery. It courses anterior to the interventricular septum in the anterior interventricular groove, extending from the base of the heart to its apex. Around the apex, the LAD anastomosis with the terminal branches of the posterior descending artery (branch of the right coronary artery).
Atherosclerosis or thrombotic occlusion of LAD causes myocardial infarction in large areas of the anterior, septal, and apical portions of the heart muscle. It can lead to a serious deterioration in heart performance.

Occlusion of the LAD causes anteroseptal myocardial infarction, which is evident on the ECG with changes in leads V1-V4. Occlusion of the left circumflex artery causes lateral, posterior, or anterolateral MI. However, as it does not run towards the apex in the interventricular septum of the heart, it is not the correct answer for this question.

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

The right coronary artery supplies the right atrium, right ventricle, interatrial septum, and the inferior posterior third of the interventricular septum. Occlusion of the right coronary artery causes inferior MI, which is indicated on ECG with changes in leads II, III, and aVF.

Recommendations from the British Thoracic Society for acute severe asthma or life-threatening asthma are:

1. Give controlled supplementary oxygen to all hypoxemic patients with acute severe asthma titrated to maintain a SpO₂ level of 94 98%.
2. Use high-dose inhaled ?₂ agonists as first-line agents in patients with acute asthma and administer them as early as possible. Reserve
intravenous ?₂ agonists for those patients in whom inhaled therapy cannot be used reliably.
3. Give steroids in adequate doses to all patients with an acute asthma attack.
4. Add nebulized ipratropium bromide (0.5 mg 4–6 hourly) to ?₂ agonist treatment for acute severe or life-threatening asthma or those with a poor initial response to ?₂ agonist therapy.
5. Consider aminophylline for children with severe or life-threatening asthma unresponsive to maximal doses of bronchodilators and steroids.

A review (including 12 case reports, three RCTs, and five other observational studies) of ketamine use in adults and children in status asthmaticus reported that ketamine is a potential bronchodilator. Still, prospective trials are needed before conclusions about effectiveness can be drawn.

Heliox has no place in the current guidelines issued by the British Thoracic Society.

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.

Since an arterial pressure transducer, and every other measuring apparatus, is prone to errors due to offset and gradient drifts, regular calibration is required to maintain accuracy of the instrument. The two-point calibration pressure values of 0 mmHg and 200 mmHg are within the physiologic range and can best compensate for the gradient drift.

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.

Blood vessels (except capillaries and venules) have three distinctive layers (innermost to outermost):
1. Tunica intima
2. Tunica media
3. Tunica adventitia

The tunica media contains smooth muscle cells and is separated from the intima layer by the internal elastic lamina and the adventitia by the external elastic lamina.

It is well known that atropine will cross the placenta and that maternal administration results in an increase in fetal heart rate.

Atropine is highly selective for muscarinic receptors. Its potency at nicotinic receptors is much lower, and actions at non-muscarinic receptors are generally undetectable clinically. Atropine does not distinguish among the M1, M2, and M3 subgroups of muscarinic receptors. In contrast, other antimuscarinic drugs are moderately selective for one or another of these subgroups. Most synthetic antimuscarinic drugs are considerably less selective than atropine in interactions with nonmuscarinic receptors.

A study on glycopyrrolate, a quaternary ammonium salt, was found to have a fetal: maternal serum concentration ratio of 0.4 indicating partial transfer.

Heparin, suxamethonium, and vecuronium do not cross the placenta.

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 superior phrenic artery branches from the thoracic aorta.

The Number Needed to Treat (NNT) is the number of patients you need to treat to prevent one additional bad outcome. For example, if a drug has an NNT of 5, it means you have to treat 5 people with the drug to prevent one additional bad outcome.

To calculate the NNT, you need to know the Absolute Risk Reduction (ARR); the NNT is the inverse of the ARR:

NNT = 1/ARR

Where ARR = CER (Control Event Rate) – EER (Experimental Event Rate).

NNTs are always rounded up to the nearest whole number.

In this case, the NNT can be computed as follows:

ARR = 10% – 5% = 0.05

NNT = 1/0.05 = 20

Carbon dioxide absorbs the most infrared (IR) light between the wavelengths of 4.2-4.4m (4.26m is ideal).

Nitrous oxide absorbs infrared light at wavelengths of 4.4-4.6m (very similar to CO2) and less so at 3.9m.

At a frequency of 4.7m, carbon monoxide absorbs the most IR light.

At 3.3 m and throughout the ranges 8-12 m, the volatile agents have strong absorption bands.

Although oxygen does not absorb infrared light, it collides with CO2 molecules, interfering with absorption. The absorption band is widened as a result of this (so called collision or pressure broadening). A drop of 0.5 percent in measured CO2 can be caused by 95% oxygen.

Nitrous oxide causes a greater inaccuracy of 0.1 percent per ten percent of nitrous oxide.

Water vapour absorbs infrared light as well, resulting in absorption band overlap, collision broadening, and partial pressure dilution. Water traps and water permeable tubing are used to reduce inaccuracies.

Collision broadening is compensated for in modern gas multi-gas analysers.

The hindgut is from the distal third of the transverse colon down to the upper one-third of the anal canal. The inferior mesenteric artery supplies the hindgut.

The inferior mesenteric artery arises from the aorta behind the inferior border of the third part of the duodenum 3–4 cm above the aortic bifurcation, at the third lumbar vertebra level.

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

The inguinal triangle of Hesselbach’s is an important clinical landmark on the posterior wall of the inguinal canal. It has the following relations:
Inferiorly – medial third of the inguinal ligament
Medially – lower lateral border of the rectus abdominis
Laterally – inferior epigastric vessels

Direct inguinal hernia is when the bowel bulges directly through the abdominal wall. These hernias usually protrude through Hesselbach’s triangle