Risk factors for sternal surgical site infection-is there any rationale for further improvement in prevention?

Abstract

Objectives: There is an increasing interest in nosocomial infections. Among those surgical site infections play a major role. Moreover in coronary bypass surgery sternal surgical site infections (SSSI) remain a significant source of morbidity and mortality. The aim of this study was to elucidate predisposing factors in order to further improve strategies of prevention. Methods: 580 consecutive patients who had isolated CABG using extracorporeal circulation were retrospectively screened by use of the institutional database (95 variables). Patients were categorized as those with SSSI (n = 19) and those without (n = 561). Data are presented as mean and range. Univariate analysis was done by contingency tables and Fisher exact test (categoric variables) or Mann-Whitney U test (non parametric continuous variables). A p < 0.05 was considered significant. Results: The overall SSSI rate was 3.2% (1.3% superficial and 1.9% deep). In most cases (n = 10) coagulase neg. staphylococci were isolated. Other species were staph. aureus, enterococci, e. coli and enterobacter. Operative mortality was higher in case of SSSI (5.3%: 2.2%). Adipositas (BMI 30.22; 22.0 to 40.7 and 27.0; 16.0 to 44.0), diabetes (Odds ratio 3.85; 95% CI 1.44 to 2.90) and terminal renal failure (Odds ratio 13.8; 95% CI 2.37 to 72.32) were found to be significant risk factors. This was not true for age, gender and general risk scores (Euro- and KCH score). Patients with SSSI had longer duration of the operation, bypass time and higher intraoperative positive fluid balance (p < 0.05). Moreover there was a significant difference in postoperative fluid balance at 12, 24 and 48h. Patients who later on suffered from SSSI exhibited higher positive values. Notably, in the group with SSSI there was a still positive fluid balance even at 48h (450 ml; -1130 to 4730 ml against -120 ml; -3990 to 7950 ml, p = 0.016). This was paralleled by a higher lactate at 24h postop.(1.3 mmol/l; 0.8 to 2.5 against 0.9 mmol/l; 0.3 to 16, p = 0.016) and max. creatinine level (1.6 mg%; 0.9 to 7.7 against 1.3 mg%; 0.5 to 10.3, p = 0.0002). The strongest predictor of infection was the need for reexploration (Odds ratio 21.98; 95% CI 8.25 to 58.57). Conclusions: Our study confirmed risk factors for SSSI as described by others. However, as risk factors not yet reported in detail signs of post ECC SIRS and postop. fluid balance were identified. By means of paying alert attention to these facts infection rates might be further reduced.