Nitrous oxide should not be utilized in patients with an air-containing confined area because it diffuses into these spaces, causing a rise in pressure. This includes circumstances like pneumothorax, intracranial air after a head injury, imprisoned air from a recent undersea dive, a recent intraocular gas injection, or intestinal blockage. Nitrous oxide increases cerebral blood flow and should be avoided in individuals who have or are at risk of having high intracranial pressure.

Flow through a tube is dependent upon:
The pressure difference across the ends of the tube (P1– P2)
The resistance to flow provided by the tube (R)
This is Darcy’s law, which is analogous to Ohm’s law in electronics:
Flow = (P1– P2) / R
Resistance in the tube is defined by Poiseuille’s law, which is determined by the diameter of the tube and the viscosity of the fluid. Poiseuille’s law is as follows:
Resistance = (8VL) / (πR4)
Where:
V = The viscosity of the fluid
L = The length of the tube
R = The radius of the tube
Therefore, in simple terms, resistance is directly proportional to the viscosity of the fluid and the length of the tube and inversely proportional to the radius of the tube. Of these three factors, the most important quantitatively and physiologically is vessel radius.
It can be seen that small changes in the radius can have a dramatic effect on the flow of the fluid. For example, the constriction of an artery by 20% will decrease the flow by approximately 60%.
Another important and frequently quoted example of this inverse relationship is that of the radius of an intravenous cannula. Doubling the diameter of a cannula increases the flow rate by 16-fold (r4). This is the reason the diameter of an intravenous cannula in resuscitation scenarios is so important.
*Please note that knowledge of the detail of Poiseuille’s law is not a requirement of the RCEM Basic Sciences Curriculum.

Glomerular filtration is a passive process. It depends on the net hydrostatic pressure across the glomerular capillaries, the oncotic pressure, and the intrinsic permeability of the glomerulus.

The mean values for glomerular filtration rate (GFR) in young adults are 130 ml/min/1.73m2 in males and 120 ml/min/1.73m2in females.

The GFR declines with age after the age of 40 at a rate of approximately 1 ml/min/year.

The Cockcroft and Gault formula overestimates creatinine in obese patients. This is because their endogenous creatinine production is less than that predicted by overall body weight.

Creatinine is used in the estimation of GFR because it is naturally produced by muscle breakdown, not toxic, not produced by the kidney, freely filtered at the glomerulus, not reabsorbed from the nephron, and does not alter GFR.

M. tuberculosis is the causative agent of pulmonary tuberculosis (TB). The most commonly used diagnostic test for the diagnosis of pulmonary TB is the direct sputum smear microscopy (DSSM) wherein the presence of acid-fast bacilli (AFB) is tested.

The most common method is the hot method or also known as Ziehl-Neelsen method. This is a staining method special for Mycobacteria species because they are known to be acid-fast which means that they are not easily decolorized by acid alcohol. Once the DSSM tests positive for acid-fast bacilli, this indicates possible infection with tuberculosis. The gold standard for diagnosis is still culture but Mycobacteria species are slow-growers that is why DSSM is considered the best diagnostic method. A positive AFB smear and correlation with symptoms is usually used by physicians to create a final diagnosis of pulmonary tuberculosis.

Cushing’s syndrome is a collection of symptoms and signs caused by prolonged exposure to elevated levels of either endogenous or exogenous glucocorticoids.

The most common cause of Cushing’s syndrome is the iatrogenic administration of corticosteroids. The second most common cause of Cushing’s syndrome is Cushing’s disease.

Cushing’s disease should be distinguished from Cushing’s syndrome and refers to one specific cause of the syndrome, an adenoma of the pituitary gland that secretes large amounts of ACTH and, in turn, elevates cortisol levels. This patient has a diagnosis of Cushing’s disease, and this is, therefore, the underlying cause in this case.

The endogenous causes of Cushing’s syndrome include:
Pituitary adenoma (Cushing’s disease)
Ectopic corticotropin syndrome, e.g. small cell carcinoma of the lung
Adrenal hyperplasia
Adrenal adenoma
Adrenal carcinoma

Digoxin directly inhibits membrane Na+/K+ ATPase, which is responsible for Na+/K+ exchange across the myocyte cell membrane. This increases intracellular Na+ and produces a secondary increase in intracellular Ca2+ that increases the force of myocardial contraction. The increase in intracellular Ca2+ occurs because the decreased Na+ gradient across the membrane reduces the extrusion of Ca2+ by the Na+/Ca2+ exchanger that normally occurs during diastole. Digoxin and K+ ions compete for the receptor on the outside of the muscle cell membrane, and so the effects of digoxin may be dangerously increased in hypokalaemia.

Advantages of LMWHGreater ability to inhibit factor Xa directly, interacting less with platelets and so may have a lesser tendency to cause bleedingGreater bioavailability and longer half-life in plasma making once daily subcutaneous administration possibleMore predictable dose response avoiding the need for routine anticoagulant monitoringLower associated risk of heparin-induced thrombocytopenia or of osteoporosis

Paroxysmal nocturnal haemoglobinuria is an acquired genetic disorder that causes a decrease in red blood cells due to a membrane defect that allows increased complement binding to RBCs, causing haemolysis. Patients complain of dark-coloured urine first in the morning due to haemoglobinuria secondary to lysis of red blood cells overnight.

Thrombosis occurs, which affects hepatic, abdominal, cerebral and subdermal veins. Thrombosis of hepatic veins can lead to Budd-Chiari syndrome, thrombosis of subdermal veins can lead to painful nodules on the skin, and thrombosis of cerebral vessels can lead to stroke. The presence of dark urine in the morning only and at no other time differentiates this condition from other conditions.

Multiple myeloma would present with bone pain, signs of radiculopathy if there were nerve root compression and a history of repeated infections.

Patients with Non-Hodgkin Lymphoma would complain of enlarged lymph nodes, fatigue, fever, weight loss and a history of repeated infections.

Acute lymphoblastic leukaemia presents more commonly in children than in adults. The patient would complain of bone pain, and on examination, there would be hepatosplenomegaly.

Typically, granuloma has Langerhan’s cells (large multinucleated cells ) surrounded by epithelioid cell aggregates, T lymphocytes and fibroblasts.

Antigen presenting monocytic cells found in the skin are known as Langerhan’s cells.

At the start of the cardiac cycle, towards the end of diastole, the whole of the heart is relaxed. The atrioventricular (AV) valves are open because the atrial pressure is still slightly greater than the ventricular pressure. The semilunar valves are closed, as the pressure in the pulmonary artery and aorta is greater than the ventricular pressures. The cycle starts when the sinoatrial node (SAN) initiates atrial systole.

Propofol (2,6-diisopropylphenol) is a short-acting phenol derivative that is primarily used for the induction of anaesthesia.
Its mechanism of action is unclear but is thought to act by potentiating the inhibitory neurotransmitters GABA and glycine, which enhances spinal inhibition during anaesthesia.
The dose for induction of anaesthesia is 1.5-2.5mg/kg. The dose for maintenance of anaesthesia is 4-12 mg/kg/hour. Following intravenous injection, propofol acts within 30 seconds and its duration of action is 5-10 minutes.
Propofol produces a 15-25% decrease in blood pressure and systemic vascular resistance without a compensatory increase in heart rate. It is negatively inotropic and decreases cardiac output by approximately 20%.
The main side effects of propofol are:
Pain on injection (in up to 30%)
Hypotension
Transient apnoea
Hyperventilation
Coughing and hiccough
Headache
Thrombosis and phlebitis

CSF analysis typically shows:
cloudy turbid appearance
raised WCC – predominantly neutrophils
high protein
low glucose (typically < 40% of serum glucose)
Gram-negative diplococci seen under microscopy

Caput medusae is a condition that consists of collateral veins radiating from the umbilicus and results from recanalization of the umbilical vein.

Under normal conditions, the portal venous blood traverses the liver and drains into the inferior vena cava of the systemic venous circulation by way of the hepatic veins. This is the direct route. However, other, smaller communications exist between the portal and systemic systems, and they become important when the direct route becomes blocked. These communications are as follows:

At the lower third of the oesophagus, the oesophageal branches of the left gastric vein (portal tributary) anastomose with the oesophageal veins draining the middle third of the oesophagus into the azygos veins (systemic tributary).

Halfway down the anal canal, the superior rectal veins (portal tributary) draining the upper half of the anal canal anastomosis with the middle and inferior rectal veins (systemic tributaries), which are tributaries of the internal iliac and internal pudendal veins, respectively.

The paraumbilical veins connect the left branch of the portal vein with the superficial veins of the anterior abdominal wall (systemic tributaries). The paraumbilical veins travel in the falciform ligament and accompany the ligamentum teres.

The veins of the ascending colon, descending colon, duodenum, pancreas, and liver (portal tributary) anastomose with the renal, lumbar, and phrenic veins (systemic tributaries).

Etomidate causes less hypotension than thiopental sodium and propofol during induction. However, it is associated with a high incidence of extraneous muscle movements, which can be minimised by an opioid analgesic or a short-acting benzodiazepine given prior to induction. Pain on injection is common and there is a high rate of thrombophlebitis in the postoperative period. Postoperative nausea and vomiting commonly occur. Etomidate suppresses adrenocortical function, particularly during continuous administration, and it should not be used for maintenance of anaesthesia. It should be used with caution in patients with underlying adrenal insufficiency, for example, those with sepsis.

The anterior triangle is the triangular area of the neck found anteriorly to the sternocleidomastoid muscle. It is formed by the anterior border of sternocleidomastoid laterally, the median line of the neck medially and by the inferior border of the mandible superiorly. The apex of the anterior triangle extends towards the manubrium sterni. The anterior triangle contains:
Muscles: thyrohyoid, sternothyroid, sternohyoid muscles
Organs: thyroid gland, parathyroid glands, larynx, trachea, esophagus, submandibular gland, caudal part of the parotid gland
Arteries: superior and inferior thyroid, common carotid, external carotid, internal carotid artery (and sinus), facial, submental, lingual arteries
Veins: anterior jugular veins, internal jugular, common facial, lingual, superior thyroid, middle thyroid veins, facial vein, submental vein, lingual veins
Nerves: vagus nerve (CN X), hypoglossal nerve (CN XII), part of sympathetic trunk, mylohyoid nerve

The posterior triangle is a triangular area found posteriorly to the sternocleidomastoid muscle. It has three borders; anterior, posterior and inferior borders. The anterior border is the posterior margin of the sternocleidomastoid muscle. The posterior border is the anterior margin of the trapezius muscle, while the inferior border is the middle one-third of the clavicle. The investing layer of deep cervical fascia and integument forms the roof of the space, while the floor is covered with the prevertebral fascia along with levator scapulae, splenius capitis and the scalene muscles. The inferior belly of omohyoid subdivides the posterior triangle into a small supraclavicular, and a large occipital, triangle.
Contents:
Vessels: the third part of the subclavian artery, suprascapular and transverse cervical branches of the thyrocervical trunk, external jugular vein, lymph nodes
Nerves: accessory nerve (CN XI), the trunks of the brachial plexus, fibers of the cervical plexus
Of the muscles listed in the options, only the anterior scalene is situated within the posterior triangle of the neck.

Atropine 500 mcg IV bolus should be administered if there are any adverse features or risk of asystole. If the reaction is not adequate, repeat the steps every 3 to 5 minutes up to a maximum dose of 3 mg. In the case of acute myocardial ischemia or myocardial infarction, atropine should be taken with caution since the increased heart rate may aggravate the ischemia or increase the size of the infarct.

Electrolytes are compounds that may conduct an electrical current and dissociate in solution. Extracellular and intracellular fluids contain these chemicals. The predominant cation in extracellular fluid is sodium, whereas the major anion is chloride. Potassium is the most abundant cation in the intracellular fluid, while phosphate is the most abundant anion. These electrolytes are necessary for homeostasis to be maintained.

The gluteal muscles are a group of muscles that make up the buttock area. These muscles include: gluteus maximus, gluteus medius. and gluteus minimus.
The gluteus maximus is the most superficial as well as largest of the three muscles and makes up most of the shape and form of the buttock and hip area. It is a thick, fleshy muscle with a quadrangular shape. It is a large muscle and plays a prominent role in the maintenance of keeping the upper body erect.
The innervation of the gluteus maximus muscle is from the inferior gluteal nerve.

Most cells have insulin receptors present on them which can be sequestered into the cell to inactivate them. These receptors consist of two extracellular alpha subunits which contain the insulin-binding site and two transmembrane beta subunits. Because insulin is a polypeptide hormone, it must act via cell surface receptors as it is unable to readily cross the cell membrane. On binding to the receptor, the beta subunit of insulin autophosphorylation, which activates tyrosine kinase. As a result, there is an intracellular cascade of phosphorylation, causing a translocation of the glucose transporter GLUT4 and GLUT-1 to the plasma membrane of the affected cell. This facilitates glucose entry.

Cefuroxime and other cephalosporin antibiotics are bactericidal ß-lactam antibiotics. They work similarly to penicillins in that they prevent cross-linking between the linear peptidoglycan polymer chains that make up the bacterial cell wall. As a result, they prevent the formation of cell walls.
The following is a summary of the various mechanisms of action of various types of antimicrobial agents:

1) Inhibition of cell wall synthesis
Penicillins
Cephalosporins
Vancomycin

2) Disruption of cell membrane function
Polymyxins
Nystatin
Amphotericin B

3) Inhibition of protein synthesis
Macrolides
Aminoglycosides
Tetracyclines
Chloramphenicol

4) Inhibition of nucleic acid synthesis
Quinolones
Trimethoprim
5-nitroimidazoles
Rifampicin

5) Anti-metabolic activity
Sulphonamides
Isoniazid

The Likelihood Ratio (LR) is the likelihood that a given test result would be expected in a patient with the target disorder compared to the likelihood that that same result would be expected in a patient without the target disorder.

The LR is used to assess how good a diagnostic test is and to help in selecting an appropriate diagnostic tests or sequence of tests. They have advantages over sensitivity and specificity because they are less likely to change with the prevalence of the disorder, they can be calculated for several levels of the symptom/sign or test, they can be used to combine the results of multiple diagnostic test and they can be used to calculate post-test probability for a target disorder.

A LR greater than 1 produces a post-test probability which is higher than the pre-test probability. An LR less than 1 produces a post-test probability which is lower than the pre-test probability. When the pre-test probability lies between 30 and 70 per cent, test results with a very high LR (say, above 10) rule in disease. An LR below 1 produces a post-test probability les than the pre-test probability. A very low LR (say, below 0.1) virtually rules out the chance that the patient has the disease.

The Likelihood Ratio (LR) is the likelihood that a given test result would be expected in a patient with the target disorder compared to the likelihood that that same result would be expected in a patient without the target disorder.

The LR is used to assess how good a diagnostic test is and to help in selecting an appropriate diagnostic tests or sequence of tests. They have advantages over sensitivity and specificity because they are less likely to change with the prevalence of the disorder, they can be calculated for several levels of the symptom/sign or test, they can be used to combine the results of multiple diagnostic test and they can be used to calculate post-test probability for a target disorder.

A LR greater than 1 produces a post-test probability which is higher than the pre-test probability. An LR less than 1 produces a post-test probability which is lower than the pre-test probability. When the pre-test probability lies between 30 and 70 per cent, test results with a very high LR (say, above 10) rule in disease. An LR below 1 produces a post-test probability les than the pre-test probability. A very low LR (say, below 0.1) virtually rules out the chance that the patient has the disease.

Treatment should be commenced with antibiotics immediately before laboratory confirmation due to the potentially life-threatening nature of the disease.

In a hospital setting, 2g of IV ceftriaxone (80 mg/kg for a child) or IV cefotaxime (2 g adult; 80 mg/kg child) are the drugs of choice.
In the prehospital setting, IM benzylpenicillin can be given as an alternative.

The characteristics of Horner’s syndrome are pupil constriction, partial ptosis and anhidrosis.

Categorical data or data that is ordered is Ordinal data e.g. disease staging system, pain scoring system.

Disease staging system is the correct answer

The adrenal glands produce too little steroid hormones, which causes Addison’s disease. The production of glucocorticoids, mineralocorticoids, and sex steroids are all altered. The most prevalent cause is autoimmune adrenalitis, which accounts for 70-80 percent of cases.

It affects more women than males and occurs most frequently between the ages of 30 and 50.

The following are some of the clinical signs and symptoms of Addison’s disease:

Weakness and sluggishness
Hypotension is a condition in which the blood pressure (notably orthostatic hypotension)
Vomiting and nausea
Loss of weight
Axillary and pubic hair loss
Depression
Hyperpigmentation is a condition in which a person’s (palmar creases, buccal mucosa and exposed areas more commonly affected)
The following are the classic biochemical hallmarks of Addison’s disease:
Hyponatraemia
Hyperkalaemia
Hypercalcaemia
Hypoglycaemia
Acidosis metabolica
When ACTH levels are combined with cortisol levels, it is possible to distinguish between primary and secondary adrenal insufficiency:
In primary insufficiency, levels rise.
In secondary insufficiency, levels are low or low normal.

Hand-foot syndrome in children is typically the first symptom of the disease, produced by infarction of the metaphysis of small bones. The disease is inherited as an autosomal recessive trait. By adulthood, the spleen has usually infarcted. Infection with the B19 parvovirus is usually followed by an aplastic crisis. Thrombocytopenia is caused by splenic sequestration.

Acute lymphoblastic leukaemia (ALL) is caused by an accumulation of lymphoblasts in the bone marrow and is the most common malignancy of childhood. The incidence of ALL is highest at 3 – 7 years, with 75% of cases occurring before the age of 6. 85% of cases are of B-cell lineage. Haematological investigations reveal a normochromic normocytic anaemia with thrombocytopenia in most cases. The total white cell count may be decreased, normal or increased. The blood film typically shows a variable number of blast cells. The bone marrow is hypercellular with >20% blast cells.

The glossopharyngeal nerve, which is responsible for the afferent pathway of the gag reflex, the vagus nerve, which is responsible for the efferent pathway of the gag reflex, and the spinal accessory nerve all exit the skull through the jugular foramen. These nerves are most frequently affected if the jugular foramen is compressed. As a result, the patient’s gag reflex is impaired.

The vestibulocochlear nerve is primarily responsible for hearing. The trigeminal nerve provides sensation in the face. The facial nerve innervates the muscles of face expression (including those responsible for closing the eye). Tongue motions are controlled mostly by the hypoglossal nerve.

The common peroneal nerve often referred to as the common fibular nerve, is a major nerve that innervates the lower extremity. It is one of the two major branches off the sciatic nerve and receives fibres from the posterior divisions of L4 through S2 nerve roots. The common peroneal nerve separates from the sciatic nerve in the distal posterior thigh proximal to the popliteal fossa. After branching off of the sciatic nerve, it continues down the thigh, running posteroinferior to the biceps femoris muscle, and crosses laterally to the head of the lateral gastrocnemius muscle through the posterior intermuscular septum. The nerve then curves around the fibular neck before dividing into two branches, the superficial peroneal nerve (SPN) and the deep peroneal nerve (DPN). The common peroneal nerve does not have any motor innervation before dividing; however, it provides sensory innervation to the lateral leg via the lateral sural nerve.

The superficial peroneal nerve innervates the lateral compartment of the leg, and the deep peroneal nerve innervates the anterior compartment of the leg and the dorsum of the foot. These two nerves are essential in the eversion of the foot and dorsiflexion of the foot, respectively. The superficial and deep peroneal nerves provide both motor and sensory innervation.

The most common presentation with common peroneal nerve injury or palsy is acute foot drop, although symptoms may be progressive and can include sensory loss or pain. Weakness in foot eversion may occur if the superficial peroneal nerve component is involved.

The nerves that supply the adductor magnus muscle have an embryologic origin from the anterior divisions of the lumbosacral plexus and include the obturator nerve, posterior division (L2-4), and the tibial portion of the sciatic nerve (L4). It is innervated by the posterior division of the obturator nerve.

Benzodiazepines are used to treat symptoms in patients with acute alcohol withdrawal syndrome.
Benzodiazepines are contraindicated in:
Respiratory depression
Marked neuromuscular respiratory weakness, such as unstable myasthenia gravis
Obstructive sleep apnoea syndrome (symptoms may be aggravated)
Severe hepatic impairment (the elimination half-life of diazepam may be prolonged; increased risk of coma)
Phobic or obsessional states, chronic psychosis or hyperkinesis (paradoxical reactions may occur).

Currently, ceftriaxone in combination with azithromycin or doxycycline is the combination of antibiotics used in the treatment of gonorrhoea.

Cryptococcus neoformans typically causes a chronic lymphocytic meningitis in immunosuppressed patients or those with intense exposure e.g. pigeon fanciers.

Anaphylaxis is a type I hypersensitivity reaction that is severe and life-threatening. It is marked by the fast onset of life-threatening airway and/or circulatory issues, which are generally accompanied by skin and mucosal abnormalities. When an antigen attaches to specific IgE immunoglobulins on mast cells, degranulation and the release of inflammatory mediators takes place (e.g. histamine, prostaglandins, and leukotrienes).

The most important medicine for treating anaphylactic responses is adrenaline. It decreases oedema and reverses peripheral vasodilation as an alpha-adrenergic receptor agonist. Its beta-adrenergic effects widen the bronchial airways, enhance the force of cardiac contraction, and inhibit the release of histamine and leukotriene. The first medicine to be given is adrenaline, and the IM route is optimal for most people.

In anaphylaxis, age-related dosages of IM adrenaline are:
150 mcg (0.15 mL of 1:1000) for a child under 6 years
300 mcg (0.3 mL of 1:1000) for a child aged 6 to 12 years
500 mcg (0.5 mL of 1:1000) for children aged 12 and above
500 mcg for adults (0.5 mL of 1:1000)

Carbon dioxide is transported in the blood from tissues to the lungs in three ways as bicarbonate ions (60%), as carbamino compounds with proteins (30%) or simply dissolved in plasma (10%).

Meta-analysis is a quantitative, formal, epidemiological study design used to systematically assess previous research studies to derive conclusions about that body of research. Outcomes from a meta-analysis may include a more precise estimate of the effect of treatment or risk factor for disease, or other outcomes, than any individual study contributing to the pooled analysis. The examination of variability or heterogeneity in study results is also a critical outcome.
The benefits of meta-analysis include a consolidated and quantitative review of a large, and often complex, sometimes apparently conflicting, body of literature. The specification of the outcome and hypotheses that are tested is critical to the conduct of meta-analyses, as is a sensitive literature search.

Important medical questions are typically studied more than once, often by different research teams in different locations. In many instances, the results of these multiple small studies of an issue are diverse and conflicting, which makes the clinical decision-making difficult. The need to arrive at decisions affecting clinical practise fostered the momentum toward evidence-based medicine. Evidence-based medicine may be defined as the systematic, quantitative, preferentially experimental approach to obtaining and using medical information. Therefore, meta-analysis, a statistical procedure that integrates the results of several independent studies, plays a central role in evidence-based medicine.

For anaesthesia, nitrous oxide is commonly used in a concentration of around 50 – 66% in oxygen in association with other inhalation or intravenous agents. Nitrous oxide cannot be used as the sole anaesthetic agent due to lack of potency, but is useful as part of a combination of drugs since it allows reduction in dosage of other agents. Exposure to nitrous oxide for prolonged periods, either by continuous or by intermittent administration, may result in megaloblastic anaemia as a result of interference with the action of vitamin B12. Nitrous oxide increases cerebral blood flow and should be avoided in patients with, or at risk of, raised intracranial pressure. Nitrous oxide may be administered by any trained personnel experienced in its use.

The composition of immunoglobulin molecules is two identical heavy and two identical light chains. These chains are linked by disulphide bridges and are each have highly variable regions which give the immunoglobulin its specificity. In addition, they have constant regions and there is virtual complete correspondence in amino acid sequence in all antibodies of a given isotype.
Five isotypes of immunoglobulin exist – these are IgG, IgA, IgM, IgE and IgD. They are determined by the heavy chain (gamma, alpha, mu, epsilon or delta respectively). The light chains are either kappa or lambda.

In most neurones the resting potential has a value of approximately -70 mV. The threshold potential is generally around -55 mV. Initial depolarisation occurs as a result of a Na+influx through ligand-gated Na+channels. Action potential is an all or nothing response; because the size of the action potential is constant, the intensity of the stimulus is coded by the frequency of firing of a neuron. Repolarisation occurs primarily due to K+efflux.