Endocrine, Nutritional, and Metabolic Disorders
Core concepts
Master the hyperglycemic emergencies: diabetic ketoacidosis (DKA) and hyperosmolar hyperglycemic state (HHS). In DKA, treat with fluids, insulin, and potassium replacement - check potassium before insulin. Understand thyroid storm and myxedema coma, adrenal crisis, and pheochromocytoma. Know stress-dose steroids in refractory shock and the physiology of critical illness-related corticosteroid insufficiency. Address nutritional support: timing of enteral feeding, refeeding syndrome (hypophosphatemia, hypokalemia, hypomagnesemia), and glycemic control in the ICU.
Traps
In DKA, total body potassium is depleted even if serum potassium is normal or high - replace potassium before or alongside insulin. Insulin drives potassium intracellularly and can precipitate dangerous hypokalemia. In adrenal crisis, give hydrocortisone before or with fluids; do not wait for confirmatory testing. Refeeding syndrome can cause fatal arrhythmias - monitor phosphate, potassium, and magnesium when starting nutrition in malnourished patients. Thyroid storm is a clinical diagnosis; do not delay treatment for labs.
Worked example
A patient with DKA has a serum potassium of 5.2 mEq/L. Because potassium is not low, insulin can be started, but potassium must be monitored closely and replaced as it falls; if potassium were <3.3 mEq/L, insulin should be held until potassium is corrected. Rule of thumb: in DKA, check potassium first; if low, replete before insulin.