The Wolff-Parkinson-White syndrome (WPWS) is linked to an additional electrical conduction pathway between the atria and ventricles. This accessory pathway (bundle of Kent), unlike the atrioventricular (AV) node, is incapable of slowing down a rapid rate of atrial depolarization. In other words, a short circuit bypasses the AV node. Patients with a rapid ventricular response or narrow complex AV re-entry tachycardia are more likely to develop atrial fibrillation or flutter.

Digoxin can promote impulse transmission through this accessory pathway if a patient with WPWS develops atrial fibrillation because it works by blocking the AV node. This can cause ventricular fibrillation and an extremely rapid ventricular rate. As a result, it’s not advised.

Adenosine, beta-blockers, and calcium channel blockers, among other drugs that interfere with AV nodal conduction, are also generally contraindicated.

The class III antiarrhythmic drugs amiodarone and ibutilide (K+ channel block) and procainamide (Na+ channel block) are the drugs of choice.

Hypochondriasis is an illness anxiety disorder, and describes excessively worriedness about the presence of a disease. While the woman is concerned about her possibility of developing motor neurone disease, she understands that no symptoms have yet appeared. Hypochondriasis involves patients who refuse to accept that they don’t have the disease, even if the results come back negative.

Late Look Bias occurs when the data is gathered or analysed at an inappropriate time e.g. when many of the subjects suffering from a fatal disease have died. This type of biasness might occur in some retrospective studies of motor neurone disease, but is not applicable to this prospective study.

In procedure bias, the researcher decides assignment of a treatment versus control and assigns particular patients to one group or the other non-randomly. This is unlikely to have occurred in this case, although it is not mentioned specifically. Of all the options, lead time-bias is a better answer.

The Hawthorne Effect refers to groups modifying their behaviour simply because they are aware of being observed. Any differences in the behaviour have not been mentioned in the question, and it is highly unlikely that a change in patient’s behaviour would have affected their length of survival in this case.

The correct option is lead-time bias. Even if the new blood test diagnoses the disease earlier, it doesn’t affect the outcome, as the survival time was still on average 43 months from the onset of symptoms in both groups. With the help of blood test, the disease was only detected 8 months earlier.

The internal carotid artery passes through the carotid canal in the petrous part of the temporal bone into the cranial cavity. It does NOT groove the sphenoid bone.

The internal carotid artery gives off no branches in the neck and is a terminal branch of the common carotid artery.

These structures pass between the external and internal carotid arteries: the styloglossus and stylopharyngeus muscles, the glossopharyngeal nerve (CN IX), and the pharyngeal branch of the vagus.

Accompanied by its sympathetic plexus, the internal carotid artery, passes through the cavernous sinus and is crossed by the abducent nerve.

Severity of a reduction in restrictive defect (%FVC) or obstructive defect (%FEV1/FVC) predicted are classified as follows:

Mild 70-80%
Moderate 60-69%
Moderately severe 50-59%
Severe 35-49%
Very severe <35% This patient has a %FVC predicted of 60.4% and this corresponds to a moderate restrictive deficit. %FEV1/FVC ratio is 93.5%. FEV1/FVC ratio 80% < predicted and VC < 80% = mixed picture. FEV1/FVC ratio 80% < predicted and VC > 80% = obstructive picture.

FEV1/FVC ratio 80% > predicted and VC > 80% = normal picture.

FEV1/FVC ratio 80% > predicted and VC < 80% predicted= restrictive picture. The integrity of the alveolar-capillary barrier is measured by carbon monoxide transfer factor (TLCO) and carbon monoxide transfer coefficient (KCO). These values are seen to be reduced in emphysema, interstitial lung diseases and in pulmonary vascular pathology. However, the KCO (as % predicted) is high in extrapulmonary restriction (pleural, chest wall and respiratory neuromuscular disease), and in loss of lung units provided the structure of the lung remaining is normal. The KCO distinguishes extrapulmonary (high KCO) causes of ‘restriction’ from intrapulmonary causes (low KCO).

Taste sensation from the anterior two-thirds of the tongue is carried by chorda tympani, a branch of the facial nerve.

The general somatic sensation of the anterior two-third of the tongue is supplied by the lingual nerve, a branch of the mandibular nerve.

Both general somatic sensation and taste from the posterior third of the tongue are carried by the glossopharyngeal nerve.

All the muscles of the tongue except palatoglossus are supplied by the hypoglossal nerve whereas palatoglossus is supplied by the vagus nerve. (This is because palatoglossus is the only tongue muscle derived from the fourth branchial arch)

Omitted variable bias occurs when a statistician passes over one or more relevant variables from the study.

Publication bias occurs in publish academic research. it occurs when the results of the study effect the decision whether to publish or not.

Expectation bias occurs when the expectation of a researcher about the results effect the behaviour of the participants. Expectations may come from communication and experiences.

Work up bias occurs in the study of diagnostic test validity, whether a gold standard procedure has been used. work up bias can seriously affect the specificity of the test.

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. Recall bias is more potential for Case-control studies.

The sternocleidomastoid muscle divides the neck into anterior and posterior triangles on both sides of the neck.

The posterior triangle has the following boundaries:
anteriorly – sternocleidomastoid muscle
posteriorly – trapezius
roof – investing layer of deep cervical fascia
floor – prevertebral fascia overlying splenius capitis, levator scapulae, and the scalene muscles

The contents of the posterior triangle are:
1. fat
2. lymph nodes (level V)
3. accessory nerve
4. cutaneous branches of the cervical plexus (A major branch of this plexus is the phrenic nerve, which arises from the anterior divisions of spinal nerves C3-C5)
5. inferior belly of omohyoid
6. branches of the thyrocervical trunk (transverse cervical and suprascapular arteries)
7. third part of the subclavian artery
8. external jugular vein

The patellar (knee jerk) reflex is a monosynaptic stretch reflex arising from L2-L4 nerve roots. It occurs after a tap on the patellar tendon which causes the spindles of the quadriceps muscles to stretch.

The afferent nerve pathway occurred through A gamma fibres.

Wesphal’s sign refers to a reduction, or absence of the patellar reflex. It is often indicated of a neurological disease affecting the PNS.

A transection of the spinal cord results in a degree of shock which causes all reflexes to be reduced or completely absent, and required a period of approximately 6 weeks to recover.

There are two types of defibrillators
AC defibrillator
DC defibrillator

AC defibrillator,
consists of a step-up transformer with primary and secondary winding and two switches. Since secondary coil consists of more turns of wire than the primary coil, it induces larger voltage. A voltage value ranging between 250V to 750V is applied for AC external defibrillator. And used to enable the charging of a capacitor.

DC defibrillator,
consists of auto transformer T1 that acts as primary of the high voltage transformer T2. Is an iron core that transfers energy between 2 circuits by electromagnetic induction. Transformers are used to isolate circuits, change impedance and alter voltage output. transformers do not convert AC to DC.

Diode rectifier composed of 4 diodes made of semiconductor material allows current to flow only in one direction. Alternating current (AC) passing through these diodes produces direct current (DC). Capacitor stores the charge in the form of an electrostatic field.

Capacitor is used to convert the rectified AC voltage to produce DC voltage but capacitors do not directly convert AC to DC.

Inductor induces a counter electromotive force(emf) that reduces the capacitor discharge value.

In step-down transformer primary coils has more turns of wire than secondary coil, so induced voltage is smaller in the secondary coil.

Femoral nerve lesion (L2,L3 and L4) is characterised by weakness of the quadriceps femoris muscle. This results in weakness of extension of the knee, loss of sensation over the front of the thigh, and loss of the knee jerk reflex.

The skin over the lateral aspect of the thigh and knee, and the lower lateral quadrant of the buttock is supplied by the lateral cutaneous nerve of the thigh (L1,2).

The adductors of the hip are supplied by the obturator nerve (L2-4). This nerve also supplies sensation to the inner thigh.

Staphylococcus aureus infection is the most likely cause.

Surgical site infections (SSI) occur when there is a breach in tissue surfaces and allow normal commensals and other pathogens to initiate infection. They are a major cause of morbidity and mortality.

SSI comprise up to 20% of healthcare associated infections and approximately 5% of patients undergoing surgery will develop an SSI as a result.
The organisms are usually derived from the patient’s own body.

Measures that may increase the risk of SSI include:
-Shaving the wound using a single use electrical razor with a disposable head
-Using a non iodine impregnated surgical drape if one is needed
-Tissue hypoxia
-Delayed prophylactic antibiotics administration in tourniquet surgery, patients with a prosthesis or valve, in clean-contaminated surgery of in contaminated surgery.

Measures that may decrease the risk of SSI include:
1. Intraoperatively
– Prepare the skin with alcoholic chlorhexidine (Lowest incidence of SSI)
-Cover surgical site with dressing

In contrast to previous individual RCT’s, a recent meta analysis has confirmed that administration of supplementary oxygen does not reduce the risk of wound infection and wound edge protectors do not appear to confer benefit.

2. Post operatively
Tissue viability advice for management of surgical wounds healing by secondary intention

Use of diathermy for skin incisions
In the NICE guidelines the use of diathermy for skin incisions is not advocated. Several randomised controlled trials have been undertaken and demonstrated no increase in risk of SSI when diathermy is used.

The basilic vein is one of the primary veins that drain the upper limb, like the cephalic vein. It begins as the dorsal venous arch. The basilic vein originates from the ulnar side of the dorsal arch of the upper limb passes along the posteromedial aspect of the forearm, moving towards the anterior surface of the elbow.

The basilic vein pierces the deep fascia at the elbow and joins the venae commitantes of the brachial vein to form the axillary vein.

The basilic vein passes deep under the muscles as it moves midway up the humerus. At the lower border of the teres major muscle, the anterior and posterior circumflex humeral veins feed into it.

Standard wire gauge cannulas for intravenous and intraarterial use are available (SWG or G). The SWG is a former imperial unit (which requires metric conversion). The cross sectional area of wires is becoming more popular as a size measurement.

The number of wires that will fit into a standard hole template is referred to as SWG.

This standard sized hole can accommodate 22 thin wires side by side (each wire the diameter of a 22 gauge cannula)
In the same hole, 14 thicker wires would fit (each wire the diameter of a 14 gauge cannula)

While the diameter and thus radius of a parallel sided tube are the most important determinants of fluid flow rate, they are not commonly used to compare cannula sizes.

The circumference of French gauge (FG) catheters (urinary or chest drains) is measured. Sizes of double lumen tracheal tubes are FG. Internal diameter is used to measure single lumen tubes.

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

The diaphragm has three opening through which different structures pass from the thoracic cavity to the abdominal cavity:

Inferior vena cava passes at the level of T8.

Oesophagus, oesophageal vessels and vagi at T10.

Aorta, thoracic duct and azygous vein through T12.

Sympathetic trunk and pulmonary branches of vagus nerve form a posterior pulmonary plexus at the root of the lung. Fibres continue posteriorly from superficial cardiac plexus to form Anterior pulmonary plexus. It contains vagi nerves and superficial cardiac plexus. These fibres then follow the blood vessel and bronchi into the lungs.

The lower border of the pleura is at the level of:

8th rib in the midclavicular line

10th rib in the lower level of midaxillary line

T12 at its termination.

Both lungs have oblique fissure while right lung has transverse fissure too.

The trachea expands from the lower edge of the cricoid cartilage (at the level of the 6th cervical vertebra) to the carina.

Cell membrane pore formation, Bacterial DNA damage, Peptidoglycan cross-linking inhibition, and peptidoglycan synthesis inhibitor are always lethal and such mechanisms are possible only in bactericidal drugs. But Protein synthesis inhibition would only prevent cell replication or cell growth and is responsible for bacteriostatic effects of the drug.

Adenosine is the first line for AV nodal re-entry tachycardia. An initial dose of 6 mg is given, and a consequent second dose or third dose of 12 mg is administered if the initial dose fails to terminate the arrhythmia.

Aside from Adenosine, a vagal manoeuvre (e.g. carotid massage) is done to help terminate the supraventricular arrhythmia.

Amiodarone is not a first-line drug for supraventricular tachycardias. Digoxin and Propranolol can be considered if the arrhythmia is of a narrow complex irregular type. Verapamil is an alternative to Adenosine if the latter is contraindicated.

The nerve stimulators deliver a stimulus lasting for 1-2 milliseconds (not second) to perform nerve blockage.

There are just 2 leads (not 3); one for the skin and other for the needle.

Prior to the administration of the local anaesthesia, a current of 0.25 – 0.5 mA (not 1-2mA) at the frequency of 1-2 Hz is preferred.

If the needle tip is close to the nerve, muscular contraction could be possible at the lowest possible current.

Insulated needles have improved the block success rate, as the current is only conducting through needle tip.

Stimulus to the femoral nerve which is placed in the mid lingual line causes withdrawer of the quadriceps and knee extension, that’s the dancing patella ( not plantar flexion).

Randomized controlled trails will be analysed by the intention-to-treat (ITT) approach. It provides unbiased comparisons among the treatment groups. ITT analyses are done to avoid the effects of dropout, which may break the random assignment to the treatment groups in a study.

ITT analysis is a comparison of the treatment groups that includes all patients as originally allocated after randomization.

In order to include such participants in an analysis, outcome data could be imputed which involves making assumptions about the outcomes in the lost participants.

Glyceryl trinitrate (GTN) has a significant first pass metabolism. About 90% of a dose of GTN is metabolised in the liver by the enzyme glutathione organic nitrate reductase.

An INSIGNIFICANT amount of metabolism occurs in the intestinal mucosa.

There is approximately 1% bioavailability after oral administration and 38% after sublingual administration.

GTN does NOT cause gastric irritation and it is well absorbed in the gastrointestinal tract.

The volume of distribution of GTN is 2.1 to 4.5 L/kg. This is HIGH.

The following table shows the compartments and their relative oxygen reserve:
Compartment Factors Room air (mL) 100% O2 (mL)
Lung FAO2, FRC 630 2850
Plasma PaO2, DF, PV 7 45
Red blood cells Hb, TGV, SaO2 788 805
Myoglobin 200 200
Interstitial space 25 160

Oxygen reserves in the body, with room air and after oxygenation.

FAO2-alveolar fraction of oxygen rises to 95% after administration of 100% oxygen (CO2 = 5%)
FRC- Functional residual capacity – (the most important store of oxygen in the body) – 2,500-3,000 mL in medium sized adults
PaO2-partial pressure of oxygen dissolved in arterial blood (80 mmHg breathing room air and 500 mmHg breathing 100% oxygen)
DF -dissolved form (0.3%)
PV-plasma volume (3L)
TG-total globular volume (5L)
Hb-haemoglobin concentration
SaO2-arterial oxygen concentration (98% breathing air and 100% when preoxygenated)

The Purkinje system, as well as the action potentials of ventricular and atrial myocytes, have the same ionic changes. It lasts about 200 milliseconds and has a resting membrane potential, as well as fast depolarisation and plateau phases.

There are five stages to the process:

Increased Na+ and decreased K+ conductance in Phase 0 (rapid depolarisation).
1st phase (initial repolarisation) : Na+ conductance decreased, while K+ conductance increased.
Phase two (plateau phase) : Ca2+ conductance increased
Phase three (repolarisation phase) : Lower Ca2+ conductance and higher K+ conductance
4th Phase (resting membrane potential) : K+ conductance increased, Na+ conductance decreased, and Ca2+ conductance decreased.

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

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

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

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

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

The small and large intestinal walls are composed of the following common layers:
1. Mucosa
2. Submucosa
3. Muscularis Externa
4. Adventitia

Intestinal villi are highly vascular projections of the mucosal surface that cover the entire small intestinal mucosa. They increase the lumen’s surface area, which aids in absorption and digestion, the primary functions of the small intestine. Villi are large and most abundant in the duodenum and jejunum.

In both the small and large intestines, the muscularis mucosae are found within the mucosa. The myenteric nerve plexus is found innervating the muscularis externa. The mucosa is lined with columnar epithelial cells, and goblet cells may be present to secrete mucins.

A stock dose of Intravenous paracetamol available in the market is 10mg/ml. There is a recommended dose of IV paracetamol according to the profile of the patient (age, co-morbidities, weight).

Weight Recommended Dose Maximum per day
≤10 kg 7.5 mg/kg 30 mg/kg
>10 kg to ≤33 kg 15 mg/kg 60 mg/kg (not exceeding 2 g)
>33 kg to ≤50 kg 15 mg/kg 60 mg/kg (not exceeding 3 g)
>50 kg with additional risk factors for hepatotoxicity 1g 3 g
>50 kg with no additional risk factors for hepatotoxicity 1g 4 g

Special precaution must be observed for patients with hepatocellular insufficiency. The maximum dose per day should not exceed 3g.

The respiratory quotient (RQ) is the ratio of CO2 produced by the body to O2 consumed in a given amount of time.

CO2 produced / O2 consumed = RQ

CO2 is produced at a rate of 200 mL per minute, while O2 is consumed at a rate of 250 mL per minute. An RQ of around 0.8 is typical for a mixed diet.

The RQ will change depending on the energy substrates consumed in the diet. Granulated sugar is a refined carbohydrate that contains 99.999 percent carbohydrate and no lipids, proteins, minerals, or vitamins.

Glucose and other hexose sugars (glucose and other hexose sugars):
RQ=1

Fats:
RQ = 0.7

Proteins:
Approximately 0.9 RQ

Ethyl alcohol is a type of alcohol.

200/300 = 0.67 RQ

For complete oxidation, lipids and alcohol require more oxygen than carbohydrates.

When carbohydrate is converted to fat, the RQ can rise above 1.0. Fat deposition and weight gain are likely to occur in these circumstances.

The process used in the study is Delphi method. This method kicks off with an open ended questionnaire and uses its responses as a survey instrument for the next round in which each of the participants is asked to rate the items that the investigators have summarized on the basis of the data collected in the first round.

Any disagreement is further discussed in phases to come on the basis of information obtained from previous phases.

Nonsteroidal anti-inflammatory drugs (NSAIDs) cause bronchospasm, rhinorrhoea, and nasal obstruction in some asthma patients.

The inhibition of cyclooxygenase-1 (Cox-1) appears to be the cause of NSAID-induced reactions. This activates the lipoxygenase pathway, which increases the release of cysteinyl leukotrienes (Cys-LTs), which causes bronchospasm and nasal obstruction.

The following changes in arachidonic acid (AA) metabolism have been observed in NSAID-intolerant asthmatic patients:

Prostaglandin E2 production is low, possibly due to a lack of Cox-2 regulation.
An increase in leukotriene-C4 synthase expression and
A decrease in the production of metabolites (lipoxins) released by AA’s transcellular metabolism.

Phospholipase A produces membrane phospholipids, which are converted to arachidonic acid.

TXA2 causes vasoconstriction as well as platelet aggregation and adhesion.

PGI2 causes vasodilation and a reduction in platelet adhesion.

PGE2 is involved in parturition initiation and maintenance, as well as thermoregulation.

The cardiac action potential has several phases which have different mechanisms of action as seen below:
Phase 0: Rapid depolarisation – caused by a rapid sodium influx.
These channels automatically deactivate after a few ms

Phase 1: caused by early repolarisation and an efflux of potassium.

Phase 2: Plateau – caused by a slow influx of calcium.

Phase 3 – Final repolarisation – caused by an efflux of potassium.

Phase 4 – Restoration of ionic concentrations – The resting potential is restored by Na+/K+ATPase.
There is slow entry of Na+into the cell which decreases the potential difference until the threshold potential is reached. This then triggers a new action potential

Of note, cardiac muscle remains contracted 10-15 times longer than skeletal muscle.

Different sites have different conduction velocities:
1. Atrial conduction – Spreads along ordinary atrial myocardial fibres at 1 m/sec

2. AV node conduction – 0.05 m/sec

3. Ventricular conduction – Purkinje fibres are of large diameter and achieve velocities of 2-4 m/sec, the fastest conduction in the heart. This allows a rapid and coordinated contraction of the ventricles