Internal Medicine: Acute Killers and Chronic Disease Titration
The Internal Medicine domain tests diagnosis and management of adult disease, with emphasis on conditions that kill or disable quickly and on chronic diseases titrated over time: acute coronary syndromes, heart failure, obstructive lung disease, diabetes and its emergencies, acute kidney injury, sodium disorders and anticoagulation.
Core rules
- STEMI: reperfusion with primary PCI within 120 minutes of first medical contact; aspirin, P2Y12 inhibitor, anticoagulation, high-intensity statin; oxygen only if hypoxaemic.
- HFrEF has four prognostic pillars - ARNI/ACE inhibitor, beta-blocker, mineralocorticoid receptor antagonist and SGLT2 inhibitor - started early and titrated towards trial doses.
- DKA: glucose >250 mg/dL, pH <7.3, bicarbonate <18, ketonaemia, anion gap >10. Total body potassium is depleted even when serum K is normal; replace when K <5.2 and urine output is adequate. Insulin 0.1 U/kg/h; add dextrose when glucose falls below 200–250.
- HHS: glucose often >600 mg/dL, osmolality >320 mOsm/kg, minimal ketosis, profound dehydration.
- Hyponatraemia: confirm hypotonicity, then use urine osmolality and urine sodium. Urine osmolality >100 indicates ADH activity; urine Na <30 suggests hypovolaemia, >30 in a clinically euvolemic patient suggests SIADH. Limit correction to 8–10 mmol/L in 24 hours.
- AKI: FENa <1%, urine Na <20 and BUN/Cr >20 favour pre-renal; FENa >2% with muddy brown casts favours ATN; FENa is unreliable with diuretics.
- Thyroid: TSH is first-line; a low or inappropriately normal TSH with low free T4 indicates central hypothyroidism.
Worked example
A 68-year-old woman on hydrochlorothiazide presents with confusion. Na 118 mmol/L, serum osmolality 250 mOsm/kg, urine osmolality 520, urine Na 55, clinically euvolemic, TSH normal. Hypotonic hyponatraemia is confirmed. The high urine osmolality shows ADH is active; urine Na >30 in a euvolemic patient fits SIADH, here drug-induced. Management: stop the thiazide, fluid restriction, and 3% saline only for seizures or severe symptoms, with correction ≤8–10 mmol/L/24 h.
Traps
- Correcting sodium faster than 8–10 mmol/L/day and causing osmotic demyelination.
- Giving bicarbonate routinely in DKA; reserve it for pH <6.9.
- Assuming a normal serum potassium in DKA means total body potassium is normal.
- Attributing breathlessness in heart failure to COPD and missing the raised JVP.
- Stopping beta-blockers in heart failure unless there is cardiogenic shock.