Fluid, Electrolyte, and Acid-Base Disorders — WACS Viva & Clinical Scenarios (Nephrology)

Exam-style fluid, electrolyte, and acid-base disorders viva scenarios with examiner probes and model answers for Internal Medicine candidates.

Scenarios covered

• SCENARIO 1: A 58-year-old male with small cell lung carcinoma presents to the emergency department with acute confusion, lethargy, and generalised tonic-clonic seizures. Laboratory evaluation reveals serum sodium of 108 mmol/L, serum osmolality of 230 mOsm/kg, urine osmolality of 520 mOsm/kg, and urine sodium of 68 mmol/L. Thyroid and adrenal functions are normal, and he is clinically euvolaemic. Formulate an immediate emergency resuscitation plan, establish target correction limits, and describe the pathophysiological consequences of over-rapid sodium correction.
• SCENARIO 2: A 64-year-old female with known chronic kidney disease presents with profound generalised muscular weakness. Her 12-lead electrocardiogram demonstrates loss of P waves, marked PR prolongation, marked widening of the QRS complex into a sine-wave appearance, and tall peaked T waves. Her serum potassium is 7.8 mmol/L. Outline your immediate stepwise medical resuscitation protocol and justify each pharmacological intervention.
• SCENARIO 3: An obtunded 24-year-old male is brought to the medical emergency room with deep, rapid respirations (Kussmaul breathing). Arterial blood gas on room air shows pH 7.12, PaCO₂ 18 mmHg, PaO₂ 96 mmHg, and HCO₃⁻ 6 mmol/L. Serum electrolytes reveal sodium 138 mmol/L, potassium 5.2 mmol/L, and chloride 94 mmol/L. Explain the systematic step-by-step interpretation of this acid-base disorder, calculate the anion gap and delta-delta ratio, and list the differential diagnoses based on these calculations.
• SCENARIO 4: A 42-year-old female presents with persistent muscle cramps and lightheadedness. Laboratory findings reveal arterial blood pH 7.54, PaCO₂ 48 mmHg, serum bicarbonate 38 mmol/L, potassium 2.6 mmol/L, and chloride 82 mmol/L. Detail your diagnostic approach to determine the underlying cause of this metabolic alkalosis using urinary electrolytes and state the principles of targeted management.
• SCENARIO 5: A 52-year-old male with multiple myeloma presents with severe dehydration, progressive drowsiness, nausea, and abdominal pain. Serum corrected calcium is 3.85 mmol/L (15.4 mg/dL), serum creatinine is 280 micromol/L, and electrocardiogram shows a shortened QT interval. Detail the acute multi-phase pharmacological and supportive management of this hypercalcaemic crisis.