100+ Free HKCA Final MCQ Practice Questions

Explanation: The first clinical step for hypoxemia during OLV is to check ETT/bronchial blocker position, then apply CPAP (e.g., 5 cm H2O) to the non-dependent (non-ventilated) lung. This supplies oxygen to the blood shunting through the collapsed lung, significantly reducing the shunt fraction. Dependent lung PEEP is also useful but CPAP to the non-dependent lung is more effective and specifically targets the shunt. Clamping the pulmonary artery is a surgical maneuver used as a last resort. High tidal volumes in the dependent lung should be avoided to prevent ventilator-induced lung injury (VILI) and increased shunt.

Explanation: Ergometrine (or Syntometrine, which contains ergometrine) is an ergot alkaloid that causes vasoconstriction and can lead to severe hypertension, coronary artery spasm, and myocardial ischemia. It is relatively contraindicated in patients with hypertension, pre-eclampsia, and coronary artery disease. Carboprost is a prostaglandin F2-alpha analogue that causes bronchoconstriction and is contraindicated in asthmatics, not pre-eclampsia. Oxytocin and misoprostol are safe to use in pre-eclampsia.

Explanation: If laryngospasm does not respond to deepening of anesthesia, Larson's maneuver, and CPAP, the definitive management is neuromuscular blockade. Succinylcholine (1-2 mg/kg IV or 4 mg/kg IM) should be administered to relax the laryngeal muscles. In the presence of severe hypoxia and bradycardia, atropine (20 mcg/kg) is often given alongside succinylcholine, but the primary pathology is airway obstruction requiring relaxants. Cricothyrotomy is a last resort. Propofol (0.5-1 mg/kg IV) can treat partial laryngospasm but is less reliable than succinylcholine for severe, persistent spasm with bradycardia.

Explanation: In severe aortic stenosis, the cardiac output is fixed due to the stenotic valve. To maintain coronary perfusion pressure, it is critical to maintain systemic vascular resistance (SVR) and avoid hypotension. The heart rate should be kept slow-to-normal (50-70 bpm) to maximize diastolic filling time and reduce myocardial oxygen demand. Tachycardia reduces diastolic time and can precipitate myocardial ischemia. While preload must be maintained, aggressive fluids can cause pulmonary congestion. Vasodilators should be avoided because they drop afterload, which severe AS patients cannot compensate for.

Explanation: Hypocapnia causes cerebral vasoconstriction by raising extracellular pH in brain tissue, which reduces cerebral blood volume and intracranial pressure (ICP). However, extreme hypocapnia can cause cerebral ischemia. The current guidelines recommend avoiding hyperventilation in the first 24 hours unless there is acute herniation, and maintaining a lower PaCO2 limit of 30-35 mmHg (4.0-4.7 kPa) to prevent ischemia.

Explanation: The ASRA guidelines for LAST recommend using 20% lipid emulsion (Intralipid). The protocol is: an initial IV bolus of 1.5 mL/kg (lean body mass) over approximately 1 minute, followed immediately by a continuous infusion of 0.25 mL/kg/min. If cardiovascular stability is not restored, the bolus can be repeated, and the infusion rate can be increased to 0.5 mL/kg/min.

Explanation: EBP has a higher failure rate if performed within the first 24 hours of dural puncture. It is highly effective (>85% success rate) when performed after 24 hours, using 15-20 mL of autologous blood injected under sterile conditions. Larger volumes (e.g., 50 mL) are associated with back pain and spinal cord compression. The blood should not be heparinized.

Explanation: The primary, definitive treatment for malignant hyperthermia is dantrolene. The starting dose is 2.5 mg/kg IV, repeated as necessary (up to 10 mg/kg or more) until the symptoms (hypercapnia, tachycardia, rigidity) are controlled. Supportive measures like sodium bicarbonate, cooling, and calcium (for hyperkalemia) are important but secondary to dantrolene.

Explanation: Patients with anterior mediastinal masses are at high risk of complete airway obstruction and cardiovascular collapse (due to compression of the tracheobronchial tree or superior vena cava/pulmonary artery) upon induction of general anesthesia, especially with neuromuscular blockade and positive pressure ventilation. The safest approach is to avoid general anesthesia if possible, performing the biopsy under local anesthesia with sedation. If general anesthesia is mandatory, spontaneous ventilation must be maintained, and a rigid bronchoscope should be available in the room.

Explanation: Postoperative delirium (POD) is an acute disturbance of consciousness, attention, and cognition that fluctuates over hours to days. It is diagnosed clinically (often using the Confusion Assessment Method, CAM). Postoperative cognitive dysfunction (POCD) is a subtle, long-term decline in cognitive function (memory, attention, concentration) that requires pre- and post-operative formal neuropsychological testing for diagnosis.