Hyperkalemia Complicating Cardiopulmonary Bypass: Analysis of Risk Factors

This study was undertaken to assess the hyperkalemic effect of several factors, including cardioplegia containing 25 mEq K⁺ per liter. We measured potassium balance at termination of cardiopulmonary bypass (CPB) in each of 20 patients with hyperkalemia (minimum K⁺, 6.0 mEq/L) and 20 patients with normal potassium levels (K⁺ up to 5.5 mEq/L) by subtracting urinary excretion of potassium from the sum of contributions from cardioplegia, hemolysis, and transfusion. The effects of potassium balance, diabetes, blood glucose, catecholamines, and propranolol on the degree of potassium change during CPB were assessed by multiple linear regression.We found no effect of potassium load on potassium change in either the hyperkalemic or normal group. This suggested that derangement of potassium homeostasis was more important than exogenous potassium loading as a hyperkalemic stimulus. Use of catecholamines reduced the potassium change in the hyperkalemic group (p < 0.048), but any effect of propranolol on potassium change was not significant.A striking finding was the frequency of diabetics in the hyperkalemic group (12 of 20 patients) compared with the control group (2 of 20) (p < 0.001). In addition, the preoperative serum glucose level in the hyperkalemic group (mean, 154 ± 75 mg/dl) exceeded that of the normal group (mean, 103 ± 13 mg/dl) (p < 0.001).It is concluded that dangerous hyperkalemia is related to derangements of potassium homeostasis rather than excessive potassium loads, and that the use of cardioplegic solutions containing 25 mEq/L of potassium is safe. Known diabetics or patients noted preoperatively to have abnormal elevations of serum glucose deserve special attention during CPB, as many hyperkalemic patients require pacing or prolongation of bypass to manage the resulting electromechanical disturbance.