Diabetes mellitus and morbidity and mortality risks after cardiac surgery

Introduction

We analyzed a database of 4367 patients (3519 male, 848 female) who underwent isolated coronary artery bypass graft (CABG) surgery at St George's Hospital between 1991 and 1998. We sought to identify pre-existing risk factors and postoperative complications among diabetic patients as opposed to nondiabetic patients that might explain the previously observed higher mortality among diabetic patients [1].

Methods

Fourteen preoperative risk factors and nine postoperative outcome measures were analyzed by appropriate statistical tests, depending on whether the data were continuous or categorical.

Results

There were no significant differences between diabetic and nondiabetic persons with regard to age; New York Heart Association classification of heart failure; requirement for preoperative intra-aortic balloon pumping; left ventricular ejection fraction; incidence of myocardial infarction or requirement for percutaneous transluminal coronary angioplasty during the 30 days before surgery; or one-, two- or three-vessel disease or total cross-clamp time. However, time spent on cardiopulmonary bypass was longer in the diabetic group: 81.2 min versus 78.6 min in the nondiabetic group (two-tailed P < 0.03). There were significant differences in pre-existing risk factors in diabetic persons versus nondiabetic persons: mean body mass index (27.3 kg/m² versus 26.6 kg/m², respectively; P < 0.00001), unstable angina (n = 251 versus n = 1244, respectively; P < 0.004), hypertension (n = 302 versus n = 1278, respectively; P < 0.000001) and renal failure requiring dialysis (n = 5 versus n = 8, respectively; P < 0.01). These differences were reflected in a higher mean Parsonnet score (5.65 for diabetic persons versus 5.48 for nondiabetic persons; two-tailed P < 0.0052).

In-hospital mortality was significantly higher in the diabetic group (n = 31 [4.83%]) than in the nondiabetic group (n = 115 [3.09%]; P < 0.02), a difference of 1.74%. In addition the diabetic group required a longer mean intensive care unit stay (2.06 days versus 1.76 days in the nondiabetic group; two-tailed P < 0.0001). Diabetic persons were at increased risk for requiring postoperative haemofiltration (P < 0.001), resuturing (P < 0.04), and post-CABG laparotomy (P < 0.002). There were no differences in requirement for postoperative intra-aortic balloon pumping, resternotomy rate, incidence of cerebrovascular accident, or requirement for tracheostomy.

Conclusion

There is a significantly greater postoperative morbidity and mortality among diabetic patients undergoing CABG surgery when compared with nondiabetic patients.