Medical Gas Supply Systems, Anaesthetic Machines, and Vaporizers — WACS Viva & Clinical Scenarios (Clinical Measurement and Equipment)

Exam-style medical gas supply systems, anaesthetic machines, and vaporizers viva scenarios with examiner probes and model answers for ANAESTHESIA candidates.

Scenarios covered

• SCENARIO 1: A 38-year-old male is undergoing an emergency exploratory laparotomy for peritonitis. Ten minutes into the procedure under general anaesthesia with isoflurane and mechanical ventilation, the master alarm sounds, indicating 'Oxygen Pipeline Pressure Loss' (pressure drops to 15 psi). Simultaneously, the oxygen-nitrous oxide proportioning system alarms. How do you immediately troubleshoot and maintain patient safety and depth of anaesthesia?
• SCENARIO 2: During an elective morning list check of an anaesthetic machine in a regional hospital, you perform the low-pressure leak test. You notice a significant pressure drop when using the universal negative-pressure leak tester on the machine outlet with the vaporizer turned ON to 2%, but no leak when the vaporizer is turned OFF. Describe your systematic diagnostic evaluation and management of this workstation fault.
• SCENARIO 3: A 65-year-old female is scheduled for a prolonged open radical nephrectomy. The theatre relies on an in-house Vacuum Insulated Evaporator (VIE) for oxygen supply, but you notice frosting on the outer jacket and the pipeline gauge reads erratic pressure fluctuations (2.8 to 5.2 bar). Detail the physical principles of a VIE, the clinical implications of this finding, and your anaesthetic contingency plan.
• SCENARIO 4: A 28-year-old primigravida is undergoing emergency caesarean section. The resident uses a classic variable-bypass isoflurane vaporizer that was recently transported from an adjacent theatre. Fifteen minutes into surgery, the patient exhibits signs of light anaesthesia despite the dial being set to 1.5%. You discover the vaporizer was inadvertently tilted during transfer. Explain the physical consequences of vaporizer tipping and your step-by-step perioperative management.
• SCENARIO 5: You are managing an emergency craniotomy in a secondary health centre where no central pipeline is available, and anaesthesia is delivered using an anaesthetic workstation supplied solely by size E oxygen and nitrous oxide cylinders. Mid-surgery, the cylinder pressure drops rapidly. Outline your approach to cylinder physics, remaining volume estimation, low-flow conservation strategies, and transition to manual resuscitation.