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Question 1
Incorrect
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A 30-year old male has Von Willebrand's disease and attends the hospital to get an infusion of desmopressin acetate. The way this works is by stimulating the release of von Willebrand factor from cells, which in turn increases factor VIII and platelet plug formation in clotting. In patients that have no clotting abnormalities, the substance that keeps the blood soluble and prevents platelet activation normally is which of these?
Your Answer: Fibrinogen
Correct Answer: Prostacyclin
Explanation: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 It was withdrawn in 2007.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 102. 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 103. 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 -
This question is part of the following fields:
- Physiology And Biochemistry
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Question 2
Correct
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Which plasma protein will bind the thyroid hormone triiodothyronine (T3) more readily?
Your Answer: Thyroxine binding globulin
Explanation:Secreted T4 and T3 circulate in the bloodstream almost entirely bound to proteins. Normally only about 0.03% of total plasma T4 and 0.3% of total plasma T3 exist in the free state. Free T3 is biologically active and mediates the effects of thyroid hormone on peripheral tissues in addition to exerting negative feedback on the pituitary and hypothalamus. The major binding protein is thyroxine-binding globulin (TBG), which is synthesized in the liver and binds one molecule of T4 or T3. About 70% of circulating T4 and T3 is bound to TBGl 10% to 15% is bound to another specific thyroid-binding protein called transthyretin (TTR). Albumin binds 15% to 20%, and 3% to lipoproteins. Ordinarily only alterations in TBG concentration significantly affect total plasma T4 and T3 levels.
Two important biological functions have been ascribed to TBG. First, it maintains a large circulating reservoir of T4 that buffers any acute changes in thyroid gland function. Second, binding of plasma T4 and T3 to proteins prevents loss of these relatively small hormone molecules in urine and thereby helps conserve iodide. TTR transports T4 in CSF and provides thyroid hormones to the CNS.
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This question is part of the following fields:
- Physiology
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Question 3
Correct
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An 85-year old female is being investigated and treated for pancytopenia of unknown origin. Her most recent blood test is shown below which shows that he has a low platelet count. Hb-102 g/l, WBC - 2.9* 109/l, Platelets - 7 * 109/l. Which of the following normally stimulates platelet production?
Your Answer: Thrombopoietin
Explanation:Interleukin-4 is a cytokine which acts to regulate the responses of B and T cells.
Erythropoietin is responsible for the signal that initiated red blood cell production.
Granulocyte-colony stimulating factor stimulates the bone marrow to produce granulocytes.
Interleukin-5 is a cytokine that stimulates the proliferation and activation of eosinophils.
Thrombopoietin is the primary signal responsible for megakaryocyte and thus platelet production.
Platelets are also called thrombocytes. They, like red blood cells, are also derived from myeloid stem cells. The process involves a megakaryocyte developing from a common myeloid progenitor cell. A megakaryocyte is a large cell with a multilobulated nucleus, this grows to become massive where it will then break up to form platelets.Immune cells are generated from haematopoietic stem cells in bone marrow. They generate two main types of progenitors, myeloid and lymphoid progenitor cells, from which all immune cells are derived.
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This question is part of the following fields:
- Physiology And Biochemistry
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Question 4
Incorrect
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Regarding sine wave damping, which one would approach equilibrium the fastest at zero amplitude, without overshoot?
Your Answer: Optimal damping
Correct Answer: Critical damping
Explanation:A damped sine wave is a smooth, periodic oscillation with an amplitude that approaches zero as time goes to infinity. In other words, the wave gets flatter as the x-values become larger.
Critical damping is defined as the threshold between overdamping and underdamping. In the case of critical damping, the oscillator returns to the equilibrium position as quickly as possible, without oscillating, and passes it once at most.
In overdamping, the system moves slowly towards the equilibrium. An underdamped system moves quickly to equilibrium, but will oscillate about the equilibrium point as it does so.
Optimal damping has a damping coefficient of around 0.64-0.7. It maximizes frequency response, minimizes overshoot of oscillations, and minimizes phase and amplitude distortion.
In an undamped system, the amplitude of the waves that are being generated remain unchanged and constant over time.
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This question is part of the following fields:
- Clinical Measurement
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Question 5
Incorrect
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Which measure of central tendency is most useful for a continuous, non-skewed data?
Your Answer: Standard deviation
Correct Answer: Mean
Explanation:Mean, also known as the average, is the most common measure of central tendency. It is the sum of all observed values divided by the number of observation. It is not useful for skewed data, which has an abnormal distribution. It is useful, instead, for numerical data that have symmetric distribution. It reflects the contributions of each data in the group, and are sensitive to outliers.
The median is the value that falls in the middle position when the observations are ranked in order from the smallest to the largest. If the number of observations is odd, the median is the middle number. If it is even, the median is the average of the two middle numbers. Unlike the mean, the median is useful on skewed data, and can be used for ordinal or numerical data if skewed.
The mode is the value that occurs with the greatest frequency in a set of observations, and is utilized for bimodal distribution.
The variance and the standard deviation are not measures of central tendency, but of dispersion.
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This question is part of the following fields:
- Statistical Methods
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Question 6
Correct
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A 32-year-old man has multiple stab wounds to his abdomen and is rushed into the emergency. Resuscitative measures are performed, but the patient remains hypotensive. Emergency laparotomy is performed, and it reveals a vessel is bleeding profusely at a certain level of lumbar vertebrae. The vessel is the testicular artery and is ligated. At which lumbar vertebrae is the testicular artery identified?
Your Answer: L2
Explanation:The important landmarks of vessels arising from the abdominal aorta at different levels of vertebrae are:
T12 – Coeliac trunk
L1 – Left renal artery
L2 – Testicular or ovarian arteries
L3 – Inferior mesenteric artery
L4 – Bifurcation of the abdominal aorta.
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This question is part of the following fields:
- Anatomy
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Question 7
Correct
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Which of the following is the best marker of mast cell degranulation in a patient with suspected anaphylaxis who became hypotensive and developed widespread urticarial rash after administration of Augmentin?
Your Answer: Tryptase
Explanation:Mast cell tryptase is a reliable marker of mast cell degranulation. Tryptase is a protease enzyme that acts via widespread protease-activated receptors (PARs).
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This question is part of the following fields:
- Pharmacology
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Question 8
Correct
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Regarding the treatment of bladder cancer, a study concerned with the usage of a combined or monotherapy was conducted. A forest plot was used for the visual representation of the data. Which of the following is true regarding forest plots?
Your Answer: Forest plots can present data from multiple studies
Explanation:Being the part of a meta analysis, forest plots are more valued as evidence then randomised control trials.
The notion that forest plots can only be used if the results are substantial is not true. They are good indicators of the significance of the data. If the diamond intersects the central line, the data is rendered significant. It also aggregates means and confidence intervals from studies conducted in the past which makes the study much more reliable as errors associated with individual studies tend to have less of an impact in this way.
The suggestion that forest plots are primarily used for qualitative data is factually incorrect. Forest plots require numerical values to function.
All in all, forest plots help us in determining whether or not there is a significant trend in that particular field of study.
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This question is part of the following fields:
- Statistical Methods
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Question 9
Correct
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A 43-year old woman, presented to the emergency department. She has suffered trauma to her right orbital floor. On examination, it is noted that her right eye is deviated upwards when compared to her left. She also has a deliberate tilt in her head to the left in an attempt to compensate for loss of intorsion. This clinical sign is caused by damage to which of the following cranial nerves?
Your Answer: Trochlear nerve
Explanation:The trochlear nerve (CN IV) is the fourth and smallest cranial nerve. It’s role is to provide somatic motor innervation of the superior oblique muscle which is responsible for oculomotion.
Injury to the trochlear nerve will result in vertical diplopia, which worsens when looking downwards or inwards. This diplopia presents as an upward deviation of the eye with a head tilt away from the site of the lesion.
The abducens nerve (CN VI) provides somatic motor innervation for the lateral rectus muscle which functions to abduct the eye. Injury to this nerve will cause diplopia and an inability to abduct the eye, causing the patient to have to rotate their head to look sideways.
The facial nerve (CN VII) provides sensory, motor and parasympathetic innervations. It’s motor aspect controls the muscles of facial expression. Damage will cause paralysis of facial expression.
The oculomotor nerve (CN III) provides motor and parasympathetic innervations. Its motor component controls most of the other extraocular muscles. Damage to it will result in ptosis, dilatation of the pupil and a down and out eye position.
The ophthalmic division of the trigeminal nerve (CN VI) is responsible for sensory innervation of skin, mucous membranes and sinuses of the upper face and scalp.
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This question is part of the following fields:
- Pathophysiology
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Question 10
Correct
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A 57-year old lady is admitted to the Emergency Department with signs of a subarachnoid haemorrhage. On admission, her GCS was 7. She has been intubated, sedated and is being ventilated and is waiting for a CT scan. Her Blood pressure is 140/70mmHg. The arterial blood gas analysis shows the following: pH 7.2 (7.35 - 7.45), PaO2 70 mmHg (80-100), PaCO2 78 mmHg (35-45), BE -3 mEq/L (-3 +/-3), Standard bic 27 mmol/L (21-27), SaO2 94%. The most likely cause of an increase in the patient's global cerebral blood flow (CBF) is which of the following?
Your Answer: Hypercapnia
Explanation:PaCO2 is one of the most important factors that regulate cerebral vascular tone. CO2 induces cerebral vasodilatation and as a result, it increases CBF. Between 20 mmHg (2.7 kPa) and 80 mmHg (10.7 kPa), there is a linear increase of PaCO2.
Sometimes, there are areas where auto regulation has failed locally but not globally. Similarly, local vs. systemic acidosis will have similar effects. When the PaO2 falls below 50 mmHg (6.5 kPa), the CBF progressively increases.
An increase in the cerebral metabolic rate for oxygen (CMRO2) and therefore CBF can be caused by hyperthermia.
A late feature of cerebral injury is hyperthermia secondary to hypothalamic injury. Therefore this is not the most likely cause of an increased CBF in this scenario. -
This question is part of the following fields:
- Physiology
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Question 11
Incorrect
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Which of the following is true about the bispectral index (BIS)?
Your Answer: Burst suppression patterns are evident at levels below 65
Correct Answer: Sevoflurane lowers BIS more than ketamine
Explanation:The bispectral index (BIS) monitors works to determine the level of consciousness of a patient by processing electroencephalographic (EEG) signals to obtain a value between 0 and 100, where 0 reflects no brain activity, and 100 reflects a patient is completely awake.
The general meaning of BIS values are:
>95: Patient is in an awake state.
65-85: Patient is in a sedated state.
40-65: Patient is in a state that is optimal for general surgery.
<40: Patient is in a deep hypnotic stateIt is important in measuring the depths of anaesthesia to prevent haemodynamic changes or patient awareness during surgery.
The nature of anaesthetic agent used is a determinant factor in resultant BIS values. Intravenous agents, such as propofol, thiopental and midazolam, result in a deeper hypnotic state, whilst inhalation agents have a lesser hypnotic effect at the same BIS values. Certain agents result in inaccurate BIS values such as ketamine and nitrous oxide (NO). These two agents appear to increase the BIS value, whilst putting the patient in a deeper hypnotic state, and should therefore not be used with BIS monitoring.
Hypothermia also affects the BIS value as it causes a 1.12 per °C decrease in body temperature.
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This question is part of the following fields:
- Clinical Measurement
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Question 12
Correct
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During a critical liver resection surgery, a 65-year-old man suffers uncontrolled hepatic bleeding. The 'Pringle manoeuvre is performed to stop the bleeding where the hepatic artery, portal vein, and common bile duct are clamped. These structures form the anterior boundary of the epiploic foramen. Which of the following vessels also contributes to the boundary of this region?
Your Answer: Inferior vena cava
Explanation:The epiploic foramen (foramen of Winslow or aditus to the lesser sac) is found behind the free right border of the lesser omentum. A short, 3 cm slit serves as the entrance to the lesser sac from the greater sac.
The epiploic foramen has the following boundaries:
Anteriorly: hepatoduodenal ligament, the bile duct (anteriorly on the right), the hepatic artery (anteriorly on the left), and the portal vein (posteriorly) together with nerves and lymphatics
Superiorly: the peritoneum of the posterior layer of the hepatoduodenal ligament runs over the caudate process of the liver
Posteriorly: inferior vena cava
Floor: upper border of the first part of the duodenum
The anterior and posterior walls of the foramen are normally
apposed, which partly explains why patients can develop large fluid
collections isolated to the greater or lesser sacRapid control of the hepatic artery and portal vein can be obtained by compression of the free edge of the lesser omentum (a €˜Pringle’ manoeuvre), which is a potentially useful technique in liver trauma and surgery.
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This question is part of the following fields:
- Anatomy
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Question 13
Correct
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Which of the following is a feature of a central venous pressure waveform?
Your Answer: An a wave due to atrial contraction
Explanation:The central venous pressure (CVP) waveform depicts changes of pressure within the right atrium. Different parts of the waveform are:
A wave: which represents atrial contraction. It is synonymous with the P wave seen during an ECG. It is often eliminated in the presence of atrial fibrillation, and increased tricuspid stenosis, pulmonary stenosis and pulmonary hypertension.
C wave: which represents right ventricle contraction at the point where the tricuspid valve bulges into the right atrium. It is synonymous with the QRS complex seen on ECG.
X descent: which represents relaxation of the atrial diastole and a decrease in atrial pressure, due to the downward movement of the right ventricle as it contracts. It is synonymous with the point before the T wave on ECG.
V wave: which represents an increase in atrial pressure just before the opening of the tricuspid valve. It is synonymous with the point after the T wave on ECG. It is increased in the background of a tricuspid regurgitation.
Y descent: which represents the emptying of the atrium as the tricuspid valve opens to allow for blood flow into the ventricle in early diastole.
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This question is part of the following fields:
- Pathophysiology
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Question 14
Incorrect
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Very small SI units are easily expressed using mathematical prefixes. One femtolitre is equal to which of the following volumes?
Your Answer: 0.000, 000, 000, 001 L
Correct Answer: 0.000, 000, 000, 000, 001 L
Explanation:Small measurement units are denoted by the following SI mathematical prefixes:
1 deci = 0.1
1 milli = 0.001
1 micro = 0.000001
1 nano = 0.000000001
1 pico = 0.000000000001
1 femto = 0.000000000000001 (used to measure red blood cell volume)
1 atto = 0.000000000000000001. -
This question is part of the following fields:
- Basic Physics
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Question 15
Correct
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Which of the following statement is correct regarding the difference between dabigatran and other anticoagulants?
Your Answer: Competitive thrombin inhibitor blocking both free and bound thrombin
Explanation:Dabigatran template is a prodrug and its active metabolite is a direct thrombin inhibitor. It is a synthetic, reversible, non-peptide thrombin inhibitor. This inhibition of thrombin results in a decrease of fibrin and reduces platelet aggregation.
Drugs like warfarin act by inhibiting the activation of vitamin K-dependent clotting factors. These factors are synthesized by the liver and activated by gamma-carboxylation of glutamate residues with the help of vitamin K. Hydroquinone form of vitamin K is converted to epoxide form in this reaction and regeneration of hydroquinone form by enzyme vitamin K epoxide reductase (VKOR) is required for this activity. Oral anticoagulants prevent this regeneration by inhibiting VKOR, thus vitamin K-dependent factors are not activated. These factors include clotting factors II, VII, IX, and X as well as anti-clotting proteins, protein C and protein S.
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This question is part of the following fields:
- Pharmacology
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Question 16
Correct
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A 74-year-old with a VVI pacemaker is undergoing a hip replacement. Which of the following is most likely to predispose him to an electrical hazard?
Your Answer: Use of cutting unipolar diathermy
Explanation:A single chamber pacemaker was implanted in the patient. In VVI mode, a pacemaker paces and senses the ventricle while being inhibited by a perceived ventricular event. The most likely electrical hazard from diathermy is electromagnetic interference (EMI).
EMI has the potential to cause the following: Inhibition of pacing
Asynchronous pacing
Reset to backup mode
Myocardial burns, and
Trigger VF.Diathermy entails the implementation of high-frequency electrical currents to produce heat and either make incisions or induce coagulation. Monopolar cautery involves disposable cautery pencils and electrosurgical diathermy units. In typical monopolar cautery, an electrical plate is placed on the patient’s skin and acts as an electrode, while the current passes between the instrument and the plate. Monopolar diathermy can therefore interfere with implanted metal devices and pacemaker function.
Bipolar diathermy, where the current passes between the forceps tips and not through the patient and is less likely to generate EMI.
Whilst the presence of a CVP line may in theory predispose the patient to microshock, the use of prerequisite CF electrical equipment makes this very unlikely. The presence of a CVP line and pacemaker does not therefore unduly increase the risk of an electrical hazard.
Isolating transformers are used to protect secondary circuits and individuals from electrical shocks. There is no step-up or step-down voltage (i.e. there is a ratio of 1 to 1 between the primary and secondary windings).
A ground (or earth) wire is normally connected to the metal case of an operating table to protect patients from accidental electrocution. In the event that a fault allows a live wire to make contact with the metal table (broken cable, loose connection etc.) it becomes live. The earth will provide an immediate path for current to safely flow through and so the table remains safe to touch. Being a low resistance path, the earth lets a large current flow through it when the fault occurs ensuring that the fuse or RCD will quickly blow. Without an operating table earth, the patient is not at more risk of an electrical hazard because of the pacemaker.
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This question is part of the following fields:
- Anaesthesia Related Apparatus
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Question 17
Incorrect
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Which of the following statement is true regarding hypoxic pulmonary vasoconstriction (HPV)?
Your Answer: The vasoconstriction occurs when the PaO2 is below 50mmHg (6.5 kPa)
Correct Answer: 20 parts per million (ppm) of nitric oxide will reduce hypoxic pulmonary vasoconstriction
Explanation:Hypoxic Pulmonary vasoconstriction (HPV) reflects the constriction of small pulmonary arteries in response to hypoxic alveoli (.i.e.; PO2 below 80-100mmHg or 11-13kPa).
These blood vessels become independent of the nerve stimulus, when blood with a high PO2 flows through the lung which contains a low alveolar PO2.
Thus a low PO2 within the alveoli has been shown to impact on hypoxic pulmonary vasoconstriction (HPV) more than a low PO2 within the blood.
HPV results in the blood flow being directed away from poorly ventilated areas of the lung and helps to reduce the ventilation/perfusion mismatch (not increase).
In animals, volatile anaesthetic agents can diminish HPV, while in adults, the evidence proves less persuading, in spite of the fact that it certainly doesn’t strengthen the effects.
HPV response will be suppressed by 20 parts per million (ppm) of nitric oxide.
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This question is part of the following fields:
- Physiology
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Question 18
Correct
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A 66-year-old man with a haemorrhagic stroke is admitted to the medical admissions unit. He has been taking warfarin for a long time because of atrial fibrillation. His INR at the time of admission was 9.1. Which of the following treatment options is the most effective in managing his condition?
Your Answer: Prothrombin complex concentrate
Explanation:Haemorrhage, including intracranial bleeding, is a common and potentially fatal side effect of warfarin therapy, and reversing anticoagulation quickly and completely can save lives. When complete and immediate correction of the coagulation defect is required in orally anticoagulated patients with life-threatening haemorrhage, clotting factor concentrates are the only viable option.
For rapid reversal of vitamin K anticoagulants, prothrombin complex concentrates (PCC) are recommended. They contain the vitamin K-dependent clotting factors II, VII, IX, and X and are derived from human plasma. They can be used as an adjunctive therapy in patients with major bleeding because they normalise vitamin K dependent clotting factors and restore haemostasis.
The most common treatments are fresh frozen plasma (FFP) and vitamin K. The efficacy of this approach is questioned due to the variable content of vitamin K-dependent clotting factors in FFP and the effects of dilution. Significant intravascular volume challenge, as well as the possibility of rare complications like transfusion-associated lung injury or blood-borne infection, are all potential issues.
To avoid anaphylactic reactions, vitamin K should be given as a slow intravenous infusion over 30 minutes. Regardless of the route of administration, the reversal of INRs with vitamin K can take up to 24 hours to reach its maximum effect.
Reversal of anticoagulation in patients with warfarin-associated intracranial haemorrhage may be considered with factor VIIa (recombinant), but its use is controversial. There are concerns about thromboembolic events following treatment, as well as questions about assessing efficacy in changes in the INR. If the drug is to be administered, patients should be screened for an increased risk of thrombosis before the drug is given.
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This question is part of the following fields:
- Pathophysiology
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Question 19
Correct
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Which of the following statements about the central venous pressure (CVP) waveform is true?
Your Answer: Third degree heart block causes canon A waves
Explanation:The central venous pressure (CVP) waveform depicts changes of pressure within the right atrium. Different parts of the waveform are:
A wave: which represents atrial contraction. It is synonymous with the P wave seen during an ECG. It is often eliminated in the presence of atrial fibrillation, and increased tricuspid stenosis, pulmonary stenosis and pulmonary hypertension.
C wave: which represents right ventricle contraction at the point where the tricuspid valve bulges into the right atrium. It is synonymous with the QRS complex seen on ECG.
X descent: which represents relaxation of the atrial diastole and a decrease in atrial pressure, due to the downward movement of the right ventricle as it contracts. It is synonymous with the point before the T wave on ECG.
V wave: which represents an increase in atrial pressure just before the opening of the tricuspid valve. It is synonymous with the point after the T wave on ECG. It is increased in the background of a tricuspid regurgitation.
Y descent: which represents the emptying of the atrium as the tricuspid valve opens to allow for blood flow into the ventricle in early diastole.
Canon waves: which refer to large waves present on the trace that do not correspond to the A, V or C waves. They usually occur in a background of complete heart blocks or junctional arrythmias.
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This question is part of the following fields:
- Clinical Measurement
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Question 20
Incorrect
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The coronary sinus is a collection of veins joined together to form a large vessel that collects blood from the myocardium. Which structure forms the largest tributary of the coronary sinus?
Your Answer: Oblique vein
Correct Answer: Great cardiac vein
Explanation:The coronary sinus is large venous structure located on the posterior aspect of the left atrium, coursing within the left atrioventricular groove. The function of the coronary sinus is to drain the venous blood from the majority of the heart. It opens into the right atrium between the opening of inferior vena cava, the fossa ovalis and the right atrioventricular orifice. The coronary sinus is often guarded by a thin, semicircular endocardial fold, also known as the thebesian valve.
Tributaries include: Great cardiac vein, middle cardiac vein, small cardiac vein, posterior vein of left ventricle, oblique vein of left atrium. The great cardiac vein is the largest tributary of the coronary sinus. -
This question is part of the following fields:
- Anatomy
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Question 21
Incorrect
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Which statement is true when describing carbonic anhydrase?
Your Answer: Has 4 isoenzymes
Correct Answer: Isoenzyme IV is found in the brush border of the proximal convoluted tubule
Explanation:Carbonic anhydrase is an enzyme which contains zinc and can be found in:
1. Erythrocytes
2. Pulmonary endothelium
3. The intestine
4. Pancreas
5. Cardiac muscle and skeletal muscle.To date, there have been seven isoenzymes identified. Of note, isoenzyme IV is found in the brush border of the proximal convoluted tubule and isoenzyme II is found within the luminal cells.
Acetazolamides a carbonic anhydrase inhibitor and is used as prophylaxis against mountain sickness and in glaucoma management.
Spironolactone is a potassium diuretic and is an aldosterone antagonist.
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This question is part of the following fields:
- Physiology
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Question 22
Incorrect
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A 60-year old male has anaemia and is being investigated. The most common combination of globin chains in a normal adult is:
Your Answer:
Correct Answer: α2β2
Explanation:There are 4 different types of globin chains which surround 4 heme molecules in haemoglobin (Hb) – α, β, γ and δ.
α chains are essential.
δ2β2 and β2γ2 are not found in a healthy adult.
97% of the Hb in a healthy adult is made of α2β2 (2 α chains and 2 β chains).
α2δ2 accounts for around 1.5-3% of the adult Hb.
α2γ2 accounts for less than 1%.With respect to oxygen transport in cells, almost all oxygen is transported within erythrocytes. There is limited solubility and only 1% is carried as solution. Thus, the amount of oxygen transported depends upon haemoglobin concentration and its degree of saturation.
Haemoglobin is a globular protein composed of 4 subunits. Haem is made up of a protoporphyrin ring surrounding an iron atom in its ferrous state. The iron can form two additional bonds – one is with oxygen and the other with a polypeptide chain.
There are two alpha and two beta subunits to this polypeptide chain in an adult and together these form globin. Globin cannot bind oxygen but can bind to CO2 and hydrogen ions.
The beta chains are able to bind to 2,3 diphosphoglycerate. The oxygenation of haemoglobin is a reversible reaction. The molecular shape of haemoglobin is such that binding of one oxygen molecule facilitates the binding of subsequent molecules.The oxygen dissociation curve (ODC) describes the relationship between the percentage of saturated haemoglobin and partial pressure of oxygen in the blood.
Of note, it is not affected by haemoglobin concentration.Chronic anaemia causes 2, 3 DPG levels to increase, hence shifting the curve to the right
Haldane effect – Causes the ODC to shift to the left. For a given oxygen tension there is increased saturation of Hb with oxygen i.e. Decreased oxygen delivery to tissues.
This can be caused by:
-HbF, methaemoglobin, carboxyhaemoglobin
-low [H+] (alkali)
-low pCO2
-ow 2,3-DPG
-ow temperatureBohr effect – causes the ODC to shifts to the right = for given oxygen tension there is reduced saturation of Hb with oxygen i.e. Enhanced oxygen delivery to tissues. This can be caused by:
– raised [H+] (acidic)
– raised pCO2
-raised 2,3-DPG
-raised temperature -
This question is part of the following fields:
- Physiology And Biochemistry
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Question 23
Incorrect
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One of the following neuromuscular blocking agents is the most potent:
Your Answer:
Correct Answer: Vecuronium
Explanation:The measure of drug potency or therapeutic response is the ED95. This is defined as the dose of a neuromuscular blocking drug required to produce a 95% depression of muscle twitch height. The ED50 and ED90 describe a depression of twitch height by 50% and 90% respectively.
The ED95 (mg/kg) of the commonly used neuromuscular blocking agents are:
suxamethonium: 0.27
rocuronium: 0.31
vecuronium: 0.04
pancuronium: 0.07
cisatracurium: 0.04
mivacurium: 0.08 -
This question is part of the following fields:
- Pharmacology
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Question 24
Incorrect
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A global cerebral blood flow (CBF) of 35 ml/100 g/min (Normal CBF = 54 ml/100 g/min) can lead to which of the following?
Your Answer:
Correct Answer: Poor prognostic EEG
Explanation:CBF is defined as the blood volume that flows per unit mass per unit time in brain tissue and is typically expressed in units of ml blood/100 g tissue/minute. The normal average CBF in adults human is about 50 ml/100 g/min, with lower values in the white matter (,20 ml/100 g/min) and greater values in the gray matter (,80 ml/100 g/min).
Low CBF levels between 30-40 ml/100 g/min may begin to show poor prognostic EEG. EEG findings consistently associated with a poor outcome are isoelectric EEG, low voltage EEG, and burst suppression (specifically burst suppression with identical bursts), as well as the absence of EEG reactivity.
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This question is part of the following fields:
- Physiology
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Question 25
Incorrect
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Which of the following antiplatelet drugs would be best for rapid offset action?
Your Answer:
Correct Answer: Epoprostenol
Explanation:Epoprostenol has a half-life of only 42 seconds and has rapid offset. It is used for the treatment of pulmonary hypertension.
Aspirin inhibits the COX enzyme irreversibly. It inhibits thromboxane synthesis but does not inhibit the enzyme thromboxane synthetase.
Ticlopidine, clopidogrel and prasugrel act as irreversible antagonists of P2 Y12 receptor of Adenosine Diphosphate (ADP). These drugs interfere with the activation of platelets by ADP and fibrinogen. Both aspirin and clopidogrel act irreversibly so they are not correct.
Paclitaxel is a long-acting antiproliferative agent used for the prevention of restenosis (recurrent narrowing) of coronary and peripheral stents and is not the correct answer.
Tirofiban has the next shortest duration of action after epoprostenol. If epoprostenol is not given in the question, it would be the best answer.
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This question is part of the following fields:
- Pharmacology
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Question 26
Incorrect
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Which term among the following is used for the proportion of a particular disease that would be eradicated from a population if the rate of disease were to be reduced to that of the group that has not been exposed to it?
Your Answer:
Correct Answer: Attributable proportion
Explanation:The attributable risk is the rate of a disease in an exposed group to that of a group that has not been exposed to it. It involves the measure of association that is pertinent to making decisions for the individuals.
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This question is part of the following fields:
- Statistical Methods
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Question 27
Incorrect
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The right coronary artery supplies blood to all the following, except which?
Your Answer:
Correct Answer: The circumflex artery
Explanation:The right coronary artery supplies the right ventricle, the right atrium, the sinoatrial (SA) node and the atrioventricular (AV) node.
The circumflex artery originates from the left coronary artery and is supplied by it.
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This question is part of the following fields:
- Anatomy
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Question 28
Incorrect
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All of the following statements are true about blood clotting except:
Your Answer:
Correct Answer: Administration of aprotinin during liver transplantation surgery prolongs survival
Explanation: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 102. 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 103. 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 -
This question is part of the following fields:
- Physiology And Biochemistry
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Question 29
Incorrect
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A 71-year-old woman will undergo surgery for a fractured femur neck. 1 mg midazolam is used to induce anaesthesia, followed by 75 mg propofol. Which of the following options best describes how these two drugs interact pharmacologically?
Your Answer:
Correct Answer: Synergism
Explanation:Drug interactions can be seen in the following examples:
Additive interaction (summation).
Additive effects are described for intravenous drug combinations such as ketamine and thiopentone or ketamine and midazolam. Different mechanisms of action are used by them. Thiopentone and midazolam are GABAA receptor agonists, whereas ketamine is an NMDA receptor antagonist. Nitrous oxide and halothane are two other examples.
Synergism is a supra-additive interaction.
Refers to the administration of two drugs with similar pharmacological properties and closely related sites of action, resulting in a combined effect that is greater than the sum of the contributions of each component. The construction of an isobologram can be used to interpret and understand these. The best example is the hypnotic effect of benzodiazepines and intravenous induction agents like propofol. As part of a co-induction technique, midazolam is frequently given before propofol.
Potentiation
In a dose-dependent manner, volatile agents enhance the effects of neuromuscular blocking agents. Electrolyte disturbance (hypomagnesaemia), Penicillin, and probenecid can all increase the effects of neuromuscular blocking agents (the latter has no similar pharmacological activity).
Infra-additive interaction (antagonism).
This can be subdivided into the following categories:
-Pharmacokinetic interference occurs when one drug affects the absorption of another through the gastrointestinal tract or when hepatic microsomal enzyme induction influences metabolism.
-Heparin and protamine, for example, or heavy metals and chelating agents, are examples of chemical antagonists.
-Competitive reversible antagonistic antagonism of receptors, such as opioids and naloxone, and irreversible antagonistic antagonism of receptors -
This question is part of the following fields:
- Pharmacology
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Question 30
Incorrect
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Which of the following factors significantly increases the risk of hepatotoxicity and fulminant hepatic failure in halothane administration?
Your Answer:
Correct Answer: Multiple exposure
Explanation:Hepatotoxicity due to halothane administration is relatively common and is a major factor in its rapidly declining use. Type 1 hepatotoxicity has an incidence of 20% to 30%. A comprehensive report in 1969 demonstrated an incidence of type 2 hepatotoxicity (hepatitis) of 1 case per 6000 to 20000 cases, with fatal cases occurring approximately once in 35000 patients following a single exposure to the anaesthetic. This incidence of fatal cases increases to approximately 1 in 1000 patients following multiple exposures. Following this study was a large-scale review in the United Kingdom, which showed similar results. To put this into perspective, there is only a single case of hepatotoxicity confirmed after the administration of desflurane and 2 cases per 1 million after enflurane. By the 1970s, halothane was the most common cause of drug-induced liver failure.
Halothane-induced hepatotoxicity has a female to male ratio of two to one. Younger patients are less likely to be affected; 80% of the cases are typically in patients 40 years or older. Other risk factors include obesity and underlying liver dysfunction. Medications such as phenobarbital, alcohol, and isoniazid may play a role in affecting CYP2E1 metabolism, increasing one’s risk.
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This question is part of the following fields:
- Pharmacology
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