USA Surgery Today

Although hyperkalemia is the most life-threatening disorder of potassium balance, hypokalemia is much more common, especially in the postsurgical patient. It most commonly results from fluid resuscitation after trauma or operative intervention without potassium supplementation. Another common cause is prolonged emesis seen in pyloric stenosis, which classically results in hyporchloremic hypokalemic metabolic alkalosis as potassium is excreted in exchange for sodium in the renal tubules. Vomiting and diarrhea from other reasons, as well as gastrointestinal losses from high output stomas or fistulae, can also lead to hypokalemia. Less commonly in the surgical patient, diuretic administration without potassium replacement may lead to hypokalemia. Diuretics induce sodium wasting and overall volume depletion, which may trigger aldosterone secretion and potentially worsen the hypokalemia. Intrinsic kidney disease may also result in potassium wasting and hypokalemia.

Signs and symptoms of hypokalemia are often subtle and may not be apparent unless there is an acute change in serum potassium concentration. Muscle weakness and ileus are the most commonly encountered and result from hyperpolarization of the muscle cells. Cardiac arrhythmias can occur, especially in patients taking digoxin. The U wave on electrocardiogram (ECG:Cardizem) is a classical sign of hypokalemia and is accompanied by low amplitude T waves. The urine potassium concentration may be useful in distinguishing among the causes of hypokalemia. In cases of hypokalemia where the urine concentration of potassium is less than 15 meq per L, appropriate conservation is being accomplished and thus losses are not due to renal dysfunction.