Respiratory Failure and Sleep-Disordered Breathing — WACS Viva & Clinical Scenarios (Respiratory Medicine)

Exam-style respiratory failure and sleep-disordered breathing viva scenarios with examiner probes and model answers for Internal Medicine candidates.

Scenarios covered

• SCENARIO 1: A 42-year-old patient presents to the emergency department 48 hours following severe acute pancreatitis with worsening tachypnoea, diaphoresis, and profound hypoxaemia. On room air, vital signs show a respiratory rate of 38 breaths per minute, SpO₂ 78%, heart rate 124 beats per minute, and blood pressure 100/65 mmHg. Arterial blood gas on 10 L/min via non-rebreather mask (estimated FiO₂ 0.80) shows pH 7.31, PaO₂ 58 mmHg, PaCO₂ 32 mmHg, HCO₃ 16 mmol/L, and base excess -8 mmol/L. Chest radiography demonstrates diffuse, bilateral alveolar infiltrates sparing the cardiophrenic angles, with a norma
• SCENARIO 2: A 68-year-old male with a 30 pack-year smoking history and known severe chronic obstructive pulmonary disease presents with acute breathlessness, productive cough with purulent sputum, and progressive somnolence. On physical examination, he is drowsy but rousable, displaying asterixis, central cyanosis, and pursed-lip breathing with marked intercostal indrawing. Arterial blood gas on uncontrolled high-flow oxygen via a simple face mask reveals: pH 7.22, PaCO₂ 78 mmHg, PaO₂ 94 mmHg, HCO₃ 31 mmol/L, and base excess +4 mmol/L. Detail the systematic pathophysiological evaluation, immediate oxygena
• SCENARIO 3: A 26-year-old female presents with ascending bilateral lower extremity weakness over 5 days, progressing to upper limb paresis, bifacial weakness, and shallow breathing. Bedside spirometry demonstrates a forced vital capacity (FVC) of 12 mL/kg (predicted normal 60-70 mL/kg) and maximum inspiratory pressure (MIP) of -18 cmH₂O. Arterial blood gas on room air shows pH 7.30, PaCO₂ 56 mmHg, PaO₂ 62 mmHg, and HCO₃ 27 mmol/L. Explain the pathophysiological basis of respiratory failure in acute neuromuscular weakness, calculate and interpret the alveolar-arterial oxygen gradient, differentiate this st
• SCENARIO 4: A 54-year-old commercial long-distance driver with a body mass index (BMI) of 41 kg/m² presents to the medical clinic with refractory hypertension, severe morning headaches, cognitive slowing, and an Epworth Sleepiness Scale score of 18/24. His spouse reports loud, disruptive habitual snoring interrupted by observed nocturnal gasping and choking episodes. Daytime arterial blood gas on room air reveals pH 7.36, PaCO₂ 49 mmHg, PaO₂ 66 mmHg, and HCO₃ 28 mmol/L. Full blood count demonstrates a haematocrit of 56%. Outline the diagnostic approach using clinical stratification tools and overnight pol
• SCENARIO 5: A candidate is presented with an arterial blood gas profile from an acutely dyspnoeic patient breathing ambient air at sea level: pH 7.49, PaO₂ 55 mmHg, PaCO₂ 28 mmHg, HCO₃ 21 mmol/L, with an atmospheric pressure (Patm) of 760 mmHg and respiratory quotient (R) assumed to be 0.8. Demonstrate the stepwise calculation of the alveolar-arterial (A-a) oxygen gradient using the alveolar gas equation, identify the primary acid-base disturbance and compensatory mechanism, classify the underlying hypoxaemic physiological mechanism, and outline the clinical differential diagnosis for this presentation.