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

T cells function as a part of the body’s adaptive immune system. There are different types of T cells, including:

Cytotoxic T cells: Function as killer cells by releasing cytotoxic granules into the membrane of targeted cells.

T-Helper cells: When activated, they function to activate other immune cell types, assist in antibody production with B cells and releasing cytokines including IL-2.

Memory T cells: Function as to provide immune memory against already encountered antigens.

T cells possess specific glycoproteins and receptors on their surface.

T-Helper cells work with HLA class II antigens on the cell surfaces in order to recognise foreign antigens

T cells survive ranges from a few weeks, to a lifetime depending on the subtype in question.

Immunoglobulins are expressed on the surface of, and secreted by B-lymphocytes.

Native antigens are recognised by B cells. T cells only recognise antigens that have been processed by the cells and presented on the surface of the cell.

The oxygen content of arterial blood can be calculated by the following equation:
(10 x haemoglobin x SaO2 x 1.34) + (PaO2 x 0.0225).
This is the sum of the oxygen bound to haemoglobin and the oxygen dissolved in the plasma.

Oxygen content x cardiac output = The amount of oxygen delivered to the tissues in unit time which is known as the oxygen flux.

Any factor that increases the metabolic demand will encourage oxygen offloading from the haemoglobin in the tissues and this causes the oxygen dissociation curve (ODC) to shift to the right. This subsequently reduced the oxygen content of arterial blood.

Conditions like fever, metabolic or respiratory acidosis lowers the oxygen content and shifts the ODC to the right.
A low level of 2,3 diphosphoglycerate (2,3-DPG) is usually related to an increased oxygen content as there is less offloading, and so the ODC is shifted to the left.

So for a given PaO2, a high blood oxygen content is related to any factors that can shift the ODC to the left and not to the right.

A low haematocrit usually means that there is a decreased haemoglobin concentration, and therefore is associated with decreased oxygen binding to haemoglobin.

A hernia is a protrusion of the abdominal viscera through a defect in the abdominal wall. Inguinal hernias are of two types; Indirect inguinal hernia and Direct inguinal hernia.
– Indirect inguinal hernia is common at young age commonly due to a patent processes vaginalis and bowel passes through the deep inguinal ring lateral to the inferior epigastric artery.
– Direct hernia forms as a result of the weakening of the posterior wall of the inguinal canal more specifically within a region called ‘Hasselbach triangle. It is defined medially by the rectus abdominis muscle, laterally by the epigastric vessels, and inferiorly by the inguinal ligament.

Direct and indirect hernias can be differentiated based on their relation to the inferior epigastric artery. Direct inguinal hernia lies medial to it while indirect inguinal hernia lies lateral to the inferior epigastric artery.

The femoral ring is the site of the femoral hernia.

The hypothalamus is primarily responsible for the regulation of the basal metabolic rate. It releases thyrotropin releasing hormones (TRH) in response to low levels of triiodothyronine (T3) and thyroxine (T4). The TRH acts on the pituitary gland to release thyroid stimulating hormone, which will stimulate the thyroid gland to synthesize more T3 and T4.

Basal metabolic rate refers to the energy expended by an individual in a resting, post-absorptive state. It represents the energy required to carry out normal body functions, such as respiration.

Myasthenic and cholinergic crises are two crises which are similar in their clinical presentation.

Myasthenic crisis can be caused by:
-lack of acetylcholine,
-poor compliance with medication,
-infection

Cholinergic crisis can be caused by excess cholinesterase inhibitor medication (mimicking organophosphate poisoning) causing excess acetylcholine.

Differentiation between the 2 crises is made by giving incremental doses of the short acting cholinesterase inhibitor, Edrophonium.
This increase acetylcholine levels and will make a myasthenic crisis better and a cholinergic crisis worse.

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

Creatinine clearance is a test used to approximate the glomerular filtration rate (GFR) as an assessment of kidney function.

Creatinine is formed during the breakdown of dietary sources of meat and skeletal muscle. It is secreted at a consistent concentration and pace into the body’s circulation, and is easily filtered across the glomerulus without being reabsorbed or metabolized by the kidney.

It is represented mathematically as:
Creatinine clearance (CL) = U x V/P
where,
U: Urinary creatinine concentration (mg/mL)
V: Volume of urine (mL/min)
P: Plasma creatinine concentration (mg/mL)

Therefore, in this case:
CL: 1.25 x 1 = 125mL/min
0.1

Ferromagnetism is the property of a substance that is magnetically attracted and can be magnetised indefinitely. A material is said to be paramagnetic if it is attracted to a magnetic field. A substance is said to be diamagnetic if it is repelled by a magnetic field.

Cobalt, iron, gadolinium, neodymium, and nickel are ferromagnetic.

Gadolinium is a ferromagnetic rare earth metal that is ferromagnetic below 20 degrees Celsius (its Curie temperature). MRI scans are enhanced with gadolinium-based contrast media.

When ferromagnetic materials are exposed to a magnetic field, they can cause a variety of issues like magnetic field interactions, heating, and image artefacts.

Titanium, lead, chromium, copper, aluminium, silver, gold, and tin are non ferromagnetic.

The pituitary gland plays a crucial role in the neuro-endocrine axis. It is located at the base of the skull in the sella turcica of the sphenoid bone. It is connected superiorly to the hypothalamus, third ventricle, and visual pathways, and laterally to the cavernous sinuses, internal carotid arteries, and cranial nerves III, IV, V, and VI.

Pituitary tumours make up about 10-15% of all intracranial tumours. The majority of adenomas are benign. Over-secretion of pituitary hormones (most commonly prolactin, growth hormone, or ACTH), under-secretion of hormones, or localised or generalised pressure effects can all cause symptoms.

Compression of the optic chiasm can result in visual field defects, the most common of which is bitemporal hemianopia. This is caused by compression of the nasal retinal fibres, which carry visual impulses from temporal vision across the optic chiasm to the contralateral sides before continuing to the optic tracts.

The interruption of the visual pathways distal to the optic chiasm causes a homonymous visual field defect. The loss of the right or left halves of each eye’s visual field is referred to as homonymous hemianopia. It’s usually caused by a middle or posterior cerebral artery territory stroke that affects the occipital lobe’s optic radiation or visual cortex.

Binasal hemianopia is a condition in which vision is lost in the inner half of both eyes (nasal or medial). It’s caused by compression of the temporal visual pathways, which don’t cross at the optic chiasm and instead continue to the ipsilateral optic tracts. Binasal hemianopia is a rare complication caused by the internal carotid artery impinging on the temporal (lateral) visual fibres.

A monocular visual loss (that is, loss of vision in only one eye) can be caused by a variety of factors, but if caused by nerve damage, the damage would be proximal to the optic chiasm on the ipsilateral side.

A central scotoma is another name for central visual field loss. Every normal mammalian eye has a scotoma, also known as a blind spot, in its field of vision. The optic disc is a region of the retina that lacks photoreceptor cells and is where the retinal ganglion cell axons that make up the optic nerve exit the retina. When both eyes are open, visual signals that are absent in one eye’s blind spot are provided for the other eye by the opposite visual cortex, even if the other eye is closed.

Scotomata can be caused by a variety of factors, including demyelinating disease such as multiple sclerosis, damage to nerve fibre layer in the retina, methyl alcohol, ethambutol, quinine, nutritional deficiencies, and vascular blockages either in the retina or in the optic nerve.

Bilateral scotoma can occur when a pituitary tumour compresses the optic chiasm, causing a bitemporal paracentral scotoma, which then spreads out to the periphery, causing bitemporal hemianopsia. A central scotoma in a pregnant woman could be a sign of severe pre-eclampsia.

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

The oxygen consumption rate (VO2) at rest is 3.5 ml/kg/minute (one metabolic equivalent or 1 MET).
3.86 ml/kg/minute thyrotoxicosis

Young children consume a lot of oxygen: around 7 ml/kg/min when they are born. The metabolic cost of breathing is higher in children than in adults, and it can account for up to 15% of total oxygen consumption. Similarly, an infant’s metabolic rate is nearly twice that of an adult, resulting in a larger alveolar minute volume and a lower FRC.

At term, oxygen consumption at rest can increase by as much as 40% (5 ml/kg/minute) and can rise to 60% during labour.

When compared to normal basal metabolism, sepsis syndrome increases VO2 and resting metabolic rate by 30% (4.55 ml/kg/minute). In septicaemic shock, VO2 decreases.

Dobutamine hydrochloride was infused into 12 healthy male volunteers at a rate of 2 micrograms per minute per kilogramme, gradually increasing to 4 and 6 micrograms per minute per kilogramme. Dobutamine was infused for 20 minutes for each dose. VO2 increased by 10% to 15%. (3.85-4.0 ml/kg/min).

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.

Number needed to treat is a measure of the impact of a treatment or intervention that is often used to communicate results to patients, clinicians, the public and policymakers. It states how many patients need to be treated for one additional patient to experience an adverse outcome (e.g. a death).

It is calculated as the inverse of the absolute risk reduction and is rounded to the next highest whole number.

The absolute risk reduction is 8% (16% – 8%). 100/8 = 12.5, so rounding up the next integer this gives at NNT of 13. i.e. you would need to give the new drug to 13 people to ensure that you prevented one death.

An acetylcholinesterase inhibitor or anticholinesterase is a chemical that inhibits the cholinesterase enzyme from breaking down acetylcholine (ACh) therefore increasing the level and duration of action of the neurotransmitter acetylcholine(ACh).

ACh stimulates postganglionic receptors to produce the following effects:

Salivation
Lacrimation
Defecation
Micturition
Sweating
Miosis
Bradycardia, and
Bronchospasm.

Since these effects are produced by muscarine, they are referred to as muscarinic effects, and the postganglionic receptors are called muscarine receptors.

SLUD (Salivation, Lacrimation, Urination, Defecation – and emesis) is usually encountered only in cases of drug overdose or exposure to nerve gases. It is a syndrome of pathological effects indicating massive discharge of the parasympathetic nervous system.

The arterial cannula inserted should have parallel walls in order to reduce the risk of interruption of blood flow to distal limbs.

It is essential that the monitor used to display the arterial pressure waves has a frequency capacity of 0.5-40Hz. This is because the pressure waves are a combination of different sine waves of varying frequencies and amplitudes.

The diameter of the catheter is directly proportional to the natural frequency which is the frequency at which the system responsible for monitoring the waves resonates and amplifies the signals. This should be at least ten fold in comparison to the fundamental frequency. The diameter of the catheter is also inversely proportional to the square root of the system compliance, the tubing length and the fluid density within the system.

The presence of an air bubble, a clot or an easily malleable diaphragm and tube can result in wave damping. Increased damping will cause a reduction in the systolic pressure, and an increase in diastolic pressure. The maximum damping value of an appropriate monitoring system would be 0.64.

A rigid, non-malleable diaphragm and tubing can cause a resonance within the system. This resonance will result in an increase in the systolic pressure and a reduction in the diastolic pressure

Potassium maintains the resting potential of cardiac myocytes, with depolarization triggered by a rapid influx of sodium ions, and repolarization due to efflux of potassium. A slow influx of calcium is responsible for the longer duration of a cardiac action potential compared with skeletal muscle.

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

The anterior tibial artery originates from the distal border of the popliteus. In the posterior compartment, it passes between the heads of the tibialis posterior and the oval aperture of the interosseous membrane to reach the anterior compartment.

On entry into the anterior compartment, it runs medially along the deep peroneal nerve.
The upper third of the artery courses between the tibialis anterior and extensor digitorum longus muscles, while the middle third runs between the tibialis anterior and extensor hallucis longus muscles.

At the ankle, the anterior tibial artery is located approximately midway between the malleoli. It continues on the dorsum of the foot, lateral to extensor hallucis longus, as the dorsalis pedis artery.

The null hypothesis states that there is no significant difference between two groups.

The alternative hypothesis states that there is a significant difference between two groups.

A type I error (false positive) occurs when a null hypothesis is rejected when it should be accepted.

A type II error (false negative) occurs when the alternative hypothesis is rejected when it should be accepted.

The probability determines the rejection of a null hypothesis.

The level of significance is set at p <0.05.

Drug A is a pure agonist for the receptor, with high intrinsic efficacy and affinity, according to the log-dose response curve.

Drug B, on the other hand, works as a competitive antagonist. It binds to the receptor but has no inherent efficacy. Drug A’s efficacy will not change, but its potency will be reduced.

A partial agonist is a drug with partial intrinsic efficacy and affinity for the receptor. Giving a partial agonist after a pure agonist will not increase receptor occupancy or decrease receptor activity, and thus will not affect drug A’s efficacy. The inverse agonist flumazenil can reverse all benzodiazepines.

An inverse agonist is a drug that binds to the receptor but has the opposite pharmacological effect.

A non-competitive antagonist is a drug that has affinity for a receptor but has different pharmacological effects and reduces the efficacy of an agonist for that receptor.

Ventricular fibrillation (VT) is an arrhythmia caused by a distortion in the organized contraction of the ventricles leading to an inability to pump blood out into the body.

Amiodarone is an anti arrhythmic drug used for the treatment of ventricular and atrial fibrillations. It is the gold standard of treatment for refractory pulseless ventricular tachycardia (VT) and ventricular fibrillation (VF).

Guidelines for emergency treatment state that only the rescuer carrying out chest compressions on the patient may stand near the defibrillator as it charges.

Cardio-pulmonary resuscitation (CPR) during cardiac arrest is required for 2 minute cycles.

Hypovolaemia is as a cause of pulseless electrical activity (PEA) can be reversed using fluid resuscitation, whereas hypotension during cardiac arrest is either persistent or undetectable and is therefore irreversible.

Hyperkalaemia and hypocalcaemia are treated using calcium salts, but calcium chloride is often preferred over calcium gluconate.

During a pulseless VT or VF, a single precordial thump will be effective if administered within the first seconds of the occurrence of a shockable rhythm.

The Delphi method relies on expert consensus. 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.

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

Paediatric life support differs from adult life support in that hypoxia is the primary cause of deterioration.

After checking for danger, the child should be given a gentle stimulus (such as holding the head and shaking the arm) and asked, Are you alright? according to current advanced paediatric life support (APLS) guidelines. Safety, Stimulate, Shout is a phrase that is frequently remembered. Any airway assessment should be preceded by these actions.

Although the algorithm includes five rescue breaths, they are performed after the airway assessment.

It is not recommended to ask parents to leave unless they are obstructing the resuscitation. A team member should be with them at all times to explain what is going on and answer any questions they may have.

CPR should not begin until the child has been properly assessed and rescue breaths have been administered.

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

It can be found as:

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

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

So,

ARR= (0.04-0.03)

ARR= 0.01

NNT= 1/0.01

NNT=100

The sacral hiatus is shaped by incomplete midline fusion of the posterior elements of the distal portion of S4 and S5. This inverted U shaped space is covered by the posterior aspect of the sacrococcygeal membrane and is an important landmark in caudal anaesthetic block. Distal most portion of the dural sac and the sacral hiatus usually terminate between levels S1 and S3. The dural sac ends at the level of S2 in adults and S3 in children.

An equilateral triangle is formed between the apex of the sacral hiatus and the posterior superior iliac spines. This triangle is used to determine the location of the sacral hiatus during caudal anaesthetic block.

The statement Epinephrine is formulated as 1 in 1000 solution means 1 gm epinephrine is present in 1000 ml of solution.

Pipeline gases (in the UK this includes: Oxygen, Nitrous oxide, Medical air, and Entonox) are supplied at 4 bar (or 400 kPa), and compressed air is supplied at 7 bar for power tools.

Carbon dioxide and nitric oxide are usually only supplied in cylinders.

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.

Doxycycline belongs to the family of tetracyclines and inhibits protein synthesis through reversible binding to bacterial 30s ribosomal subunits, which prevent binding of new incoming amino acids (aminoacyl-tRNA) and thus interfere with peptide growth.