The overstated risk of preoperative hypokalemia.

To examine the relation between preoperative hypokalemia and frequency of intraoperative arrhythmias, Holter monitoring was employed in 447 patients undergoing major cardiac or vascular operations, the group at greatest risk for life-threatening arrhythmias. Based on serum potassium levels measured immediately before surgery, 57% of patients were normokalemic (greater than or equal to 3.6 mEq/L), 34% hypokalemic (3.1-3.5 mEq/L), and 9% severely hypokalemic (less than or equal to 3.0 mEq/L). No arrhythmia occurred at any time in 63% of patients and minor arrhythmias (premature atrial and occasional premature ventricular contractions) occurred in 16%. Frequent or complex ventricular ectopy appeared before and during operation in 92 patients (21%) but was not related to preoperative potassium level or history of long-term diuretic therapy. Frequent and complex ventricular arrhythmias were more common in patients with a history of long-term digoxin therapy or congestive heart failure. Even among these patients, hypokalemia or diuretic therapy did not increase the incidence or severity of ectopy. These data fail to support the common practice of delaying operation for acute potassium replacement in patients whose preoperative serum potassium is less than normal, even in the presence of cardiovascular disease.