Preoperative serum potassium levels and perioperative outcomes in cardiac surgery patients

Context Although potassium is critical for normal electrophysiology, the as sociation between abnormal preoperative serum potassium level and periopera tive adverse events such as arrhythmias has not been examined rigorously. Objective To determine the prevalence of abnormal preoperative serum potass ium levels and whether such abnormal levels are associated with adverse per ioperative events. Design and Setting Prospective, observational, case-control study of data c ollected from 24 diverse US medical centers in a 2-year period from Septemb er 1, 1991, to September 1, 1993. Patients A total of 2402 patients (mean [SD] age, 65.1 [10.3] years; 24% fe male) undergoing elective coronary artery bypass grafting who were not enro lled in another protocol. The study population was identified using systema tic sampling of every nth patient, in which n was based on expected total n umber of procedures at that center during the study period. Main Outcome Measures Intraoperative and postoperative arrhythmias, the nee d for cardiopulmonary resuscitation (CPR), cardiac death, and death due to any cause prior to discharge, by preoperative serum potassium level. Results Perioperative arrhythmias occurred in 1290 (53.7%) of 2402 patients , with 238 patients (10.7%) having intraoperative arrhythmias, 329 (13.7%) having postoperative nonatrial arrhythmias, and 865 (36%) having postoperat ive atrial flutter or fibrillation. The incidence of adverse outcomes was 3 .6% for death, 2.0% for cardiac death, and 3.5% for CPR. Serum potassium le vel less than 3.5 mmol/L was a predictor of serious perioperative arrhythmi a (odds ratio [OR], 2.2; 95% confidence interval [CI], 1.2-4.0), intraopera tive arrhythmia (OR, 2.0; 95% CI, 1.0-3.6), and postoperative atrial fibril lation/flutter (OR, 1.7, 95% CI, 1.0-2.7), and these relationships were unc hanged after adjusting for confounders. The significant univariate associat ion between increased need for CPR and serum potassium level less than 3.3 mmol/L (OR, 3.3; 95% CI, 1.2-9.5) and greater than 5.2 mmol/L (OR, 3.0; 95% CI, 1.1-8.7) became nonsignificant after adjusting for confounders. Conclusions Perioperative arrhythmia and the need for CPR increased as preo perative serum potassium level decreased below 3.5 mmol/L. Although interve ntional trials are required to determine whether preoperative intervention mitigates these adverse associations, preoperative repletion is low cost an d low risk, and our data suggest that screening and repletion be considered in patients scheduled for cardiac surgery.