Internal Medicine and Its Subspecialties
Core concepts
Internal medicine questions cluster around common, high-mortality conditions and their evidence-based first steps: acute coronary syndrome (ECG within 10 minutes, troponin, aspirin, reperfusion), heart failure (BNP, ACE inhibitor or ARB, beta-blocker, diuretic), asthma and COPD (spirometry, inhaler technique, steroids), diabetes (HbA1c, metformin, DKA versus hyperosmolar state), chronic kidney disease (eGFR, potassium, anaemia), sepsis (cultures then antibiotics within one hour), thyroid disease, anticoagulation (INR monitoring, DOACs) and electrolyte correction.
Traps
Distinguish most likely diagnosis from next best step. Elderly and immunocompromised patients present atypically, with confusion or falls instead of classic symptoms. In diabetic ketoacidosis, total-body potassium is depleted even when serum potassium looks normal or high. Correcting sodium too quickly risks osmotic demyelination. Asymptomatic severe hypertension rarely needs intravenous therapy in the emergency department. Always ask whether a drug, not a disease, explains the presentation.
Worked example
A patient in DKA has a serum potassium of 2.9 mmol/L. Insulin drives potassium intracellularly and can precipitate a fatal arrhythmia, so hold insulin, give intravenous potassium, and recheck before starting the insulin infusion. Rule of thumb: if potassium is below 3.3 mmol/L, no insulin yet.
For hyperglycaemic hyponatraemia, use the corrected sodium: measured sodium plus 1.6 times (glucose in mg/dL minus 100) divided by 100. Do not correct faster than 8-10 mmol/L in 24 hours.
Rule of thumb
Treat the patient, not the monitor: a number alone rarely justifies a dangerous intervention.