Before I conclude the discussion of sodium and potassium, it might be useful to describe some of the clinical symptoms of electrolyte imbalance. Interestingly enough, they are very similar for low-sodium, low-potassium, and high-potassium states. They include muscle weakness, nausea, anorexia, and mental changes, which usually tend toward drowsiness and lethargy. The electrocardiogram (ECG) in hypokalemia is very characteristic, and with serum values less than 3.0 mEq/L usually shows depression of the ST segment and flattening or actual inversion of the T wave. In hyperkalemia the opposite happens: the T wave becomes high and peaked; this usually begins with serum potassium values more than 7.0 mEq/L (reference values being 4.0-5.5 mEq/L). Hypokalemia may be associated with digitalis toxicity with digitalis doses that ordinarily are nontoxic because potassium antagonizes the action of digitalis. Conversely, very high concentrations of potassium are toxic to the heart, so IV infusions should never administer more than 20.0 mEq/hour even with good renal function.

There is disagreement in the medical literature regarding preoperative detection and treatment of hypokalemia. On one hand, various reports and textbooks state that clinically significant hypokalemia (variously defined as less than 2.8, 3.0, or 3.2 mEq/L) produces a substantial number of dangerous arrhythmias. On the other hand, several investigators did not find any significant difference in intraoperative arrhythmias, morbidity, or mortality between those patients with untreated hypokalemia and those who were normokalemic.