7 - surgery mcqs - 31 to 40

31. Clostridium tetani

(a) Is a gram-negative rod
(b) Is sensitive to penicillin
(c) Is widely prevalent in both soil and the environment
(d) Releases a heat-resistant endotoxin
(e) The toxin acts on the post-synaptic membrane of inhibitory nerve fibres

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only b and c are the right answers . clostridium tetani is a gram positive rod , sensitive to pencillin and releases a heat resistant exotoxin . the toxin acts on the pre-synaptic membrane of inhibitory nerve fibres .

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32. Diathermy

(a) Works by using a direct current
(b) The frequencies used range from 400kHz to 10MHz
(c) A cutting effect is produced by using a continuous output
(d) A coagulation effect is produced by using a pulsed output
(e) Maximal current density and heating effect is seen at the point of greatest cross-sectional area

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b , c , d are the right answers . Diathermy works by using an alternating current. The frequencies used are an order of magnitude greater than those used in domestic electrical appliances (50Hz). Such high frequencies have no effect on the myocardium. The maximal current density is at the point of least cross sectional area. This is usually the tip of the forceps or point. It can however occur at other points such as the plate or a metal prosthesis if appropriate precautions are not taken.

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33. The following predispose to wound infection

(a) Malnutrition
(b) Hypovolaemia
(c) Malignancy
(d) A good wound blood supply
(e) Steroid therapy

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only d is the wrong answer .Malnutrition, hypovolaemia, malignancy and steroid therapy all predispose to wound infection. The risk of wound infection can be reduced if a competent surgical technique is used. Wounds should not be closed undertension and a good blood supply should be ensured.

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34. Lignocaine

(a) Reduce cell membrane permeability to sodium ions
(b) Acts on large myelinated A fibres before unmyelinated C fibres
(c) Has a duration of action of greater than 12 hours
(d) 20 ml of 1% lignocaine is a safe dose in a 70 kg man
(e) Addition of adrenaline allows the dose used to be safely doubled

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a , d , e are the right answers . Local anasethetics are weak bases that are ionised a physiological pHs. They act on small unmyelinated C fibres before large myleinated A fibres. As a result pain senation is abolished before touch and motor responses. Lignocaine has duration of action of about one hour. Adrenaline decreases absorption increasing the maximum safe dose and prolongs the duration of action.

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35. Hepatitis B

(a) Is a single stranded DNA virus
(b) Has an incubation period of between of between 6 weeks and 6 months
(c) More than 90% of infected patients become chronic carriers
(d) Hbe antigen positivity is associated with a high risk of the patient being an infective risk
(e) In the United Kingdom the population prevalence of the disease is about 2%

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only a ,b , d are the right answers . Hepatitis B is a single stranded DNA virus. It is a disease that is particularly prevalent amongst homosexuals, prostitutes, drug addicts and renal dialysis pateints. About 10% of patients become chronic carriers. These patients have an increased risk of cirrhosis and hepatocellular carcinoma

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36. Human immunodeficiency virus

(a) Is a single stranded DNA retrovirus
(b) Induces a fall in CD4 lymphocytes, monocytes and antigen-presenting cells
(c) Increases the risk of opportunistic infection
(d) Patients can be infective prior to seroconversion illness at about three months
(e) The median survival with AIDS is greater than 10 years

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b , c , d are the right answers . HIV is a single stranded RNA retrovirus. It induces immunodeficeincy and increases the risk of opportunitsic infection (e.g. histoplasmosis, pneumocystis carinii) and malignancy (e.g. Kaposi's sarcoma). Patients may have asymptomatic or symptomatic disease for several years before developing AIDS. The median survival with full AIDS is less than two years

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37. Serum alpha-fetoprotein is increased in

(a) Acute hepatitis
(b) Hepatocellular carcinoma
(c) Neuroblastoma
(d) Teratomas
(e) Bladder carcinoma

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a, b , c , d are the right answers . Serum alpha-fetoprotein is a fetal serum protein produced by the yolk sac and liver. Increased serum levels in adults are seen in tumours (hepatocellular carcinoma, neuroblastomas and teratoma) and acute hepatitis and colitis. In patients with tumours, serum levels often correlate with tumour size. Resection is usually associated with a fall in serum levels. Serum levels are useful in assessing response to treatment.

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38. Osmotic diuretics

(a) Reduce sodium and water reabsorption in the distal convoluted tubule
(b) Produce a diuresis limited by the glomerular filtration rate
(c) Frusemide is an osmotic diuretic
(d) Glucose can act as an osmotic diuretic
(e) Mannitol is an osmotic diuretic

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only c is the wrong answer . Frusemide is a loop diuretic. Mannitol is the most commonly used osmotic diuretic. The polyuria seen in diabetics is a result of glucose acting as an osmotic diuretic

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39. Grade I hypovolaemic shock

(a) Occurs when more than 40% of the circulating blood volume has been lost
(b) Tachycardia is a reliable clinical sign
(c) A fall in pulse pressure is observed
(d) Urine output is markedly reduced
(e) Capillary return is delayed

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only b is the right answer .Grade I shock is seen with the loss of 15% of the circulating volume. This occurs when 750 ml of blood is lost in the average 70Kg man. Tachycardia is often the only physical sign. Capillary return, blood pressure and urine output are usually maintained.

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40. During a trauma primary survey the following chest injuries should be identified

(a) Airway obstruction
(b) Tension pneumothorax
(c) Aortic disruption
(d) Traumatic diaphragmatic hernia
(e) Myocardial contusion

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only a and b are right. Airway obstruction and tension pneumothorax should be apparent during the primary survey. Aortic disruption, traumatic diaphragmatic hernia and myocardial contusion may not be identified until completion of the secondary survey.

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