Hypercapnia and surgical site infection: a randomized trial

Tissue oxygenation is a strong predictor of surgical site infection (SSI). Mild intraoperative hypercapnia increases peripheral, gastrointestinal, and splanchnic tissue oxygenation and perfusion. Hypercapnia also has anti-inflammatory effects. However, it is unknown whether hypercapnia reduces SSI risk. We tested the hypothesis that mild intraoperative hypercapnia reduces the risk of SSI in patients having colon resection surgery.

With institutional review board approval and subject consent, patients having elective colon resection (e.g. hemicolectomy and low-anterior resection) expected to last >2 h were randomly assigned to intraoperative normocapnia (PE'CO2 ≈ 35 mm Hg; n=623) or hypercapnia ( PE'CO2 ≈ 50 mm Hg; n=592). Investigators blinded to group assignment evaluated perioperative SSI (Center for Disease Control criteria) for 30 postoperative days. SSI rates were compared.

Patient and surgical characteristics were comparable among the groups. The SSI rate for normocapnia was 13.3%, and for hypercapnia, it was 11.2% (P=0.29). The Executive Committee stopped the trial after the first a priori determined statistical assessment point because of much smaller actual effect compared with the projected. However, because the actual difference found in the SSI rates (15-16%) were within the 95% confidence intervals (CIs) of the projected relative difference of 33% (95% CI -43 to +24%), our results cannot be considered as 'no difference', and cannot exclude a Type II error. Time to first bowel movement was half-a-day shorter in the hypercapnia group.

Mild hypercapnia appears to have little or-possibly-no ability to prevent SSI after colon resection. Other strategies for reducing SSI risk should thus take priority.