RCOA Guide to the FRCA Examination The Primary (fourth edition) SBAs Flashcards
A 56 year-old man with a one hour history of chest pain presents to the Emergency Department. Blood pressure is 70/45 mm Hg, heart rate 115 b/min and regular to palpation. On examination he is cyanosed and his peripheries are cold and clammy. A 12-lead ECG has not yet been performed.
The most important immediate treatment for this patient is:
a) Clopidogrel
b) Fibrinolytic therapy
c) Glyceryl trinitrate
d) High flow oxygen
e) Nifedipine
D
Although this scenario describes a probable acute coronary syndrome (ACS), insufficient clinical information is given to be certain of this. Oxygenation of the myocardium is the most important immediate goal as the patient is cyanosed. GTN may exacerbate hypotension. Aspirin and clopidogrel should be given as soon as possible if a diagnosis of ACS is confirmed (and they are not contraindicated) to prevent further thrombus formation but are not the immediate priority. Fibrinolysis is reserved for STEMI and new LBBB. ALS guidelines state that nifedipine should be avoided in ACS.
A ventilated patient has been admitted to the Intensive Care Unit after emergency major colorectal surgery and is receiving a continuous intravenous infusion of a drug to support his cardiovascular system. Blood glucose concentration 12 h later is 13 mmol/L although he is not known to be diabetic. You suspect that the choice of drug infusion may be responsible.
The drug infusion is most likely to be which of the following?
a) Adrenaline
b) Dobutamine
c) Enoximone
d) Noradrenaline
e) Vasopressin
A
Although there are several causes of hyperglycaemia in critically ill patients including the stress response, insulin resistance and TPN, an adrenaline infusion is the most likely drug from the list given to cause increased blood glucose, by stimulating glycogenolysis, gluconeogenesis and lipolysis.
A patient undergoes removal of sebaceous cyst under total intravenous general anaesthesia using propofol and alfentanil. The surgeon infiltrates local anaesthetic at the end of surgery.
Which of the following properties of alfentanil is the best reason for choosing it rather than fentanyl?
a) Clearance
b) Inactive metabolites
с) pKa
d) Potency
e) Volume of distribution
E
The key point is rapid offset of alfentanil. Its smaller volume of distribution means that it has a shorter elimination half-life than fentanyl despite its lower clearance. B is also true of fentanyl. C relates to speed of onset which is useful but not the best reason for using the drug.
An asthmatic develops severe bronchospasm after administration of diclofenac.
This is most likely to be caused by production of:
a) Arachidonic acid
b) Leukotrienes
c) Phospholipase A2
d) Prostacyclin
e) Thromboxane A2
B
The most likely reason for bronchospasm after a NSAID in an asthmatic is over-production of leukotrienes, caused by COX inhibition and shunting of arachidonic acid metabolism away from prostaglandin production.
A 12.5 kg two-year-old boy requires hernia repair as a day case. After induction of general anaesthesia a caudal block is performed using levobupivacaine for intra-operative and post-operative analgesia.
Which of the following doses is most appropriate?
a) 0.25%, 10 ml
b) 0.25%, 20 ml
c) 0.5%, 5 ml
d) 0.5%, 10 ml
e) 0.75% 3 ml
A
The maximum recommended safe dose of bupivacaine is 2mg kg’, either plain or with added adrenaline. B and Dare therefore immediately excluded. A and C both contain a safe dose of levobupivacaine 25 mg, as does E with a dose of 22.5 mg. The higher concentrations are unnecessary and more likely to lead to motor weakness. A is a better choice as the greater volume of approximately 1 ml kg’ is more likely to ascend high enough from the level of injection to cover the site of surgery effectively (iliohypogastric and ilioinguinal nerves; T11 and T12 intercostal nerves).
A patient with chronic renal failure receiving an intravenous diamorphine infusion has had a respiratory arrest.
Which of the following is the most likely cause?
a) Decreased plasma clearance of diamorphine
b) Decreased plasma volume following dialysis leading to increased plasma concentration of diamorphine
c) Impaired renal excretion of diamorphine
d) Increased plasma concentration of 6-monoacetyl morphine
e) Increased plasma concentration of morphine-6-glucuronide
E
Diamorphine hydrolysis is catalysed by abundant plasma esterases.
6-monoacety/morphine is an active metabolite, which is further metabolized to morphine. Morphine is metabolised in the liver by glucuronidation to morphine-3-glucuronide and morphine-
6-glucuronide. Impaired renal excretion and accumulation of morphine-6-glucuronide, which is thirteen times more potent than morphine with a similar half-life, is a potential hazard when morphine (or diamorphine) is given by infusion to patients with renal failure.
A new aminosteroid non-depolarising neuromuscular blocker with a similar molecular weight to rocuronium produces satisfactory intubating conditions 45 seconds after administration.
Which of the following is most likely to be a property of the new drug?
a) Clinical intubating dose 2 mg/kg
b) Greater potency than rocuronium
c) Muscle fasciculation
d) Recovery of train-of-four ratio > 0.9 within 15 minutes
e) Reversed by sugammadex
A
The correct answer is based on the Bowman principle: lower potency requires a larger clinical intubating dose, which means more molecules of the drug are given and so onset is faster according to the law of mass action. B is therefore false. Fasciculation is associated with the use of depolarising neuromuscular blockers. Recovery will be dependent on metabolism. Reversal by sugammadex may be a feature but is not the most predictable property.
An experiment is being designed to assess speed of gastric emptying. It is planned to administer a standard dose of a marker drug orally to healthy volunteers and then measure plasma drug concentrations at standard times after the oral dose.
Which of the following drugs is likely to be most useful in this experiment?
a) Aspirin
b) Morphine
c) Paracetamol
d) Propranolol
e) Vancomycin
Correct answer C.
The ideal pharmacokinetic properties required of such a marker drug are: 100% oral bioavailability, zero absorption from the stomach and rapid absorption from the small intestine. Gentamicin, vancomycin and propranolol have poor oral bioavailability. Aspirin will be absorbed from the stomach even if gastric emptying is delayed. Paracetamol is well and rapidly absorbed from the small intestine and is often used as a marker of gastric emptying.
A new phenylpiperidine opioid analgesic is found to have a potency ten times that of morphine. Its pKa is 6.1 and it is metabolised in the liver with a clearance of 10 ml/Kg.
Its volume of distribution at steady state is 8 L/Kg and it is 75% plasma protein bound.
Which of the following properties of the new drug is the most likely explanation for it having a faster onset time than fentanyl?
a) Degree of plasma protein binding
b) Hepatic clearance
с) pKa
d) Potency
e) Volume of distribution
Correct answer C.
Onset time depends on the concentration gradient between unbound, unionised drug in blood and the brain: a higher lipid solubility will favour a faster onset but this drug is less lipid soluble (lower potency than fentanyl). It has similar protein binding, so similar unbound fraction; clearance is similar to that of fentanyl.
The main difference is the lower pKa so a higher unionised fraction.
A 72-year-old patient in the Acute Medical Admissions Unit has persistent bradycardia with a blood pressure of 110/50 mm Hg. He denies chest pain or shortness of breath but has experienced several episodes of dizziness.
He is currently receiving 40% oxygen by facemask, his oxygen saturation is 96% and he looks comfortable.
His ECG shows regular p-waves at a rate of 80 min-1 and regular QRS complexes of 0.16 ms duration at a rate of 30 min.
Which of the following is the most important immediate treatment?
a) Adrenaline
b) Atropine
c) Ephedrine
d) Glucagon
e) Pacing
Correct answer B.
The ECG suggests complete heart block with broadened QRS indicating increased risk of asystole. Following ALS guidelines initial treatment of this bradycardia is atropine; pacing may be the next treatment. Glucagon may be indicated if beta-blocker or calcium channel blocker overdose is suspected. An adrenaline infusion may be indicated if atropine fails to restore sinus rhythm and there is a delay in establishing temporary transvenous pacing.
An intravenous infusion of a drug is administered to a 60 kg subject and, at steady state, urine is collected over four hours from a urinary catheter. The following data are obtained:
Plasma concentration at steady state = 25 mcg/ml
Urinary concentration = 2.5 mg/ml
Total urinary volume = 240 ml
What is the renal clearance of the substance?
a) 24 ml min-1
b) 60 ml min-1
c) 100 ml min-1
d) 120 ml min-l
e) 240 ml min-1
Correct answer C.
The renal clearance of a drug is the notional volume of plasma completely cleared of drug by renal excretion per unit time.
Hence, renal clearance = amount of drug excreted in urine per
unit time divided by plasma concentration.
Myocardial contractility may be defined as the intrinsic ability of cardiac muscle fibres to do work with a given preload and afterload.
Which of the following is the best measure of left ventricular (LV) contractility?
a) Ejection fraction
b) LV end-diastolic pressure
c) LV end-diastolic volume
d) LV end-systolic pressure
e) Stroke volume
Correct answer A.
All of the factors listed are influenced by loading conditions (preload, afterload) and/or compliance of LV. Ejection fraction is least influenced and is the best overall measure of contractility in this list.
A patient with a history of ischaemic heart disease is complaining of central chest pain following laparoscopic cholecystectomy. A 12-lead ECG shows ST elevation in leads II, Ill and aVF.
Which coronary artery is most likely to have been occluded?
a) Left anterior descending artery
b) Left circumflex artery
c) Left coronary artery
d) Posterior interventricular artery
e) Right coronary artery
Correct answer E.
The ECG changes are suggestive of an infarct of the inferior left ventricle. The right coronary artery supplies the inferior left ventricle in 90% of the population.
Oxygen delivery to skeletal muscle may increase by a factor of 50 during vigorous exercise.
Which of the following physiological changes increases oxygen delivery to skeletal muscle during exercise by the greatest multiple?
a) Decreased parasympathetic tone to skeletal muscle
b) Increased cardiac output
c) Increased partial pressure gradient for oxygen between capillary blood and mitochondria
d) Relaxation of skeletal muscle precapillary sphincters
e) Right shift of the haemoglobin-oxygen dissociation curve
Correct answer D.
Whilst all of these factors operate, relaxation of the precapillary sphincters (autoregulatory change effected by local mediators) causes skeletal muscle blood flow and hence oxygen supply to increase 20-30-fold. The increase in cardiac output is only 5-10-fold. Oxygen offload from haemoglobin may increase 2-3-fold. The partial pressure gradient for oxygen increases less than 2-fold.
The pH of venous blood is only slightly lower than that of arterial blood despite the addition of large amounts of CO2 in the tissues.
Which of the following is the best explanation for this?
a) Bohr effect
b) Buffering of H+ ions by plasma proteins
c) Carbon dioxide is very soluble in blood
d) Carbonic anhydrase activity
e) Haldane effect
Correct answer E.
The Haldane effect describes the increased capacity of deoxyhaemoglobin to carry CO2 as carbaminohaemoglobin and to buffer H+ ions (through histidine residues with a pKa 6.8) generated from the dissociation of carbonic acid. This is termed isohydric buffering.
Plasma proteins and dissolution of CO2 play a minor role in CO2 transport. Carbonic anhydrase is of course essential and plays a major role but it cannot buffer pH changes caused by addition of CO2. The Bohr effect is irrelevant.
A patient with a body mass index of 50 Kg/m2 and no other medical history of note is scheduled for surgery under general anaesthesia. The ODP has changed his position from semi-sitting to horizontal for induction of anaesthesia.
Which of the following is the most important respiratory change that will occur?
a) Chest compliance will decrease
b) Functional residual capacity will decrease
c) Inspiratory reserve volume will increase
d) Peak expiratory flow rate will decrease
e) Respiratory rate will increase
Correct answer B.
All listed changes occur. By far the most important is decreased FRC, which may now encroach on the closing volume, tending to cause an increase in shunt and hypoxaemia. It will also decrease the store of oxygen in the lungs.
Oxygen delivery to the tissues (oxygen flux) increases during normal pregnancy.
Which of the following is the most important reason for this?
a) Increased myocardial contractility
b) Increased haematocrit
c) Increased PaO2
d) Increased venous return
e) Shift of the oxygen-haemoglobin dissociation curve
Correct answer D.
Oxygen flux = CO x CaO2. CO increases by approximately 50% at
term. The main reasons for this increase are increased circulating volume (ostrogen effect) and venodilatation (progesterone effect) causing increased venous return. The increased venous return necessitates increased cardiac output. This is a situation somewhat analogous to optimising oxygen delivery using oesophaegal Doppler monitoring to guide fluid loading during surgery in high risk patients. The mechanism for increasing oxygen delivery is increased cardiac output, which is itself dependent on increased preload (increased venous return). None of the other statements is true. There is little or no change in myocardial contractility during pregnancy. Although the RBC mass is increased by 20%, haematocrit falls. There is little change in PaO2. Position of the oxyhaemoglobin curve is irrelevant to a consideration of oxygen delivery.
In an experimental situation, a giant squid axon is bathed in an electrolyte solution containing chloride, potassium and sodium ions.
Which of the following changes would have the greatest effect in making the resting membrane potential less negative?
a) Decreasing the extracellular concentration of potassium ions
b) Decreasing the extracellular concentration of sodium ions
c) Increasing the extracellular concentration of chloride ions
d) Increasing the extracellular concentration of potassium ions
e) Increasing the extracellular concentration of sodium ions
Correct answer D.
This question simply tests knowledge of the Goldman & Nernst equations and that the resting membrane is relatively impermeable to sodium.
At rest, the nerve cell is only permeable to potassium. By increasing the extracellular concentration of potassium ions, less potassium will be able to leak out of the cell down a concentration gradient. Therefore, more positively charge K+ ions remain in the cell and the cell becomes less negative.
Systemic vascular resistance (SVR) can be calculated if cardiac output has been measured.
Which of the following additional pairs of measurements is needed to calculate SVR?
a) Diastolic and systolic systemic arterial pressure
b) Diastolic systemic arterial pressure and pulmonary artery
occlusion pressure
c) Left ventricular end-diastolic pressure and mean systemic
arterial pressure
d) Mean systemic arterial pressure and central venous pressure
e) Mean pulmonary artery pressure and central venous pressure
Correct answer D.
SVR is approximately ten times PVR and is mainly at arteriolar level.
It is calculated from MAP and CVP:
SVR = k x (MAP-CVP)/CO.
In order to investigate the factors determining the ventilatory response to hypercapnia, healthy volunteers breathe through a tight-fitting facemask connected to a breathing system containing 21% oxygen and 7% carbon dioxide.
Which of the following is the most important factor that directly drives the observed change in minute ventilation?
a) Increased hydrogen ion concentration of arterial blood
b) Increased hydrogen ion concentration of CSF
c) Stimulation of the carotid bodies
d) Stimulation of central chemoreceptors by increased PaCO2
e) Stimulation of peripheral chemoreceptors by increased PaCO2
Correct answer B.
The central chemoreceptors are more important than the peripheral chemoreceptors in determining the ventilatory response to carbon dioxide. They are directly sensitive to changes in pH.
A patient is receiving oxygen therapy using a Venturi face mask with an entrainment ratio of approximately 1:10 and oxygen flow rate of 6 L/min
What is the approximate inspired oxygen concentration?
a) 24%
b) 28%
c) 35%
d) 40%
e) 60%
Correct answer B.
Oxygen concentration =
((6 × 1.0) + (60 x 0.21))/66 = 0.282 i.e. ≥ 28%
An isoflurane vapouriser calibrated at sea level is being used at high altitude. The anaesthetist uses the vapouriser making no allowance for altitude.
Maintenance of anaesthesia using a vapouriser setting of
1.0-1.5% isoflurane in air appears to run uneventfully.
Which of the following best explains why the anaesthetist may use the same dial settings on the vapouriser at high altitude as at sea level?
a) Depth of anaesthesia is titrated against clinical response not anaesthetic concentration
b) Isoflurane concentration at the vapouriser output increases
as ambient pressure decreases
c) Monitors of end-tidal vapour concentration compensate for altitude
d) Plenum vapourisers deliver the same partial pressure at any particular dial setting irrespective of ambient pressure
e) The temperature drop at higher altitudes has only minimal
effect on vapouriser function
Correct answer D.
Although all of the statements apart from C are true statements, the key reason why the vapouriser functions independently of altitude is that the vapouriser delivers a fixed partial pressure, independent of altitude.
B is a variation on D but is less able to explain the phenomenon.
For example, if the ambient pressure is 0.5 atm, the delivered concentration is 2% at a dial setting of 1%. This follows from the fact that the SVP of volatile is unchanged at altitude and the splitting ratio remains unchanged.
Ultrasound (US) machines have various controls to alter the quality of the image seen on screen.
Which of the following best explains how image quality is optimised when increasing the depth of focus from 2 cm to 6 cm?
a) More US waves are emitted from the probe
b) The wavelength of the US wave is increased
c) The image is enhanced by digital processing
d) The US transducer is recalibrated to be more sensitive
e) The US transducer output is amplified to a greater extent
Correct answer B.
Lower frequency (longer wavelength) ultrasound waves penetrate to a greater depth - at the expense of decreased resolution.
An oxygen Rotameter bobbin reads a flow rate 1 L/min. As the Rotameter needle valve is opened further, the bobbin rises up the tube and then comes to rest at a reading of 8 L/min.
Which of the following descriptions of the physics of gas flow around the bobbin best explains why the bobbin comes to rest opposite the 8 L/min marker?
a) The cross sectional area of the Rotameter tube has increased
b) The flow has become less laminar
c) The flow has become more turbulent
d) The forces acting above and below the bobbin have equalised
e) The pressure gradient across the bobbin has remained constant during its ascent
Correct answer D.
Although all statements except E are true, the reason the bobbin comes to rest is an expression of Newtonian physics where a stationary body must have equal and opposite forces applied to it. The other statements do not explain why it is brought to rest.
None of the other statements can in themselves explain why the bobbin does not continue to rise in the gas flow.
