Pathophysiology
1) decreased potassium levels < 3.5 mmol/L due to increased potassium losses, decreased potassium intake, shift of potassium intracellularly Specific causes – 2) K+ wasting diuretics (furosemide, thiazides) 3) prolonged diarrhea or vomiting 4) metabolic alkalosis 5) excessive sweating 6) hyperaldosteronism
Signs and Symptoms
1) symptoms occur if plasma K+ is < 3.0 2) weak and tired legs 3) fatigue 4) myalgias 5) hypoventilation due to respiratory muscle weakness 6) paralysis 7) nocturia, polyuria, polydipsia
Characteristic Test Findings
EKG – 1) flattening of T waves 2) presence of “u” waves
Associated Conditions
increased incidence with – 1) amphotericin B 2) steroids 3) laxative abuse 4) theophylline 5) tetracycline 6) renal cell carcinoma 7) Cushing’s syndrome 8) treatment of diabetic ketoacidosis hypokalemia causes hypertension
Biochemistry
hypokalemia causes delayed ventricular repolarization
Treatment
1) repletion either by mouth or IV (no more than 20 mmol/h) 2) correction of ongoing losses
Tips for USMLE
1) any condition with high renin will have low potassium 2) hypokalemia in setting of digitalis use can precipitate digitalis toxicity (even if levels are normal) 3)Â hypokalemia can precipitate hepatic encephalopathy in cirrhotics 4) look for hypokalemia in any question with prolonged diarrhea or vomiting.
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