Nephrology
Master the approach to acute kidney injury (AKI): prerenal, intrinsic, and postrenal, using history, volume status, urinalysis, and fractional excretion of sodium (with caveats). Know the indications for urgent dialysis (AEIOU: acidosis, electrolytes, intoxication, overload, uremia). Understand the management of hyperkalemia (stabilize the myocardium with calcium, shift potassium intracellularly, then remove it). Recognize nephrotoxic exposures and the importance of medication dose adjustment in renal impairment.
Traps
Questions test the limits of FENa: it is unreliable in diuretic use, CKD, and contrast nephropathy. Do not give calcium for hyperkalemia without ECG changes? Actually, give calcium when there are ECG changes or severe hyperkalemia; recognize that insulin/glucose and beta-agonists shift rather than remove potassium. Watch for the patient with rising creatinine after starting an ACE inhibitor or NSAID - consider hemodynamic AKI and medication adjustment. Know that contrast-associated AKI is less common than traditionally taught and that prophylactic bicarbonate is not universally recommended.
Rule of thumb
In hyperkalemia with ECG changes, give intravenous calcium first, then shift with insulin/glucose, then remove with a binder or diuresis/dialysis.