Internal Medicine
Internal medicine questions integrate acid-base interpretation, diabetes emergencies, thyroid disease, chronic kidney disease and common infections.
Acid-base
- Anion gap = Na − (Cl + HCO3); normal 8–12 mmol/L.
- High anion gap acidosis: ketoacidosis, lactate, uraemia, toxins (methanol, ethylene glycol, salicylate).
- Check the delta ratio to detect a mixed disorder.
Diabetes emergencies
- DKA: glucose usually >13.9 mmol/L, ketones present, pH <7.3, bicarbonate <18 mmol/L.
- HHS: glucose often >33 mmol/L, osmolality >320 mOsm/kg, minimal ketosis, profound dehydration.
- Treat both with isotonic saline, insulin and potassium replacement; total body potassium is depleted even when serum potassium looks normal or high.
Thyroid and kidney
- Primary hypothyroidism: high TSH with low free T4.
- CKD stages G1–G5 by eGFR; complications include anaemia, hyperkalaemia, metabolic acidosis and renal bone disease.
Infection
- Community-acquired pneumonia: CURB-65 (confusion, urea >7 mmol/L, respiratory rate ≥30, blood pressure, age ≥65) guides admission.
Worked example
A young type 1 diabetic presents with vomiting, Kussmaul breathing, glucose 25 mmol/L, pH 7.15, bicarbonate 10 mmol/L and ketonuria. This is DKA. Give isotonic saline, an insulin infusion after fluids, and replace potassium once it falls below 5.5 mmol/L with adequate urine output.
Traps
Giving bicarbonate routinely in DKA, starting insulin before fluid resuscitation, and missing a mixed acid-base disorder.