Moderate hypothermia (e.g., 34.5 °C) causes surgical site infections, but it remains unknown whether mild hypothermia (34.6 °C–35.9 °C) causes infection. Therefore, the objective of this study was to evaluate the relationship between intraoperative time-weighted average core temperature and a composite of serious wound and systemic infections in adults having colorectal surgery over a range of near-normal temperatures.

Retrospective, single center study.

The operating rooms of the Cleveland Clinic Foundation from January 2005 to December 2014.

Adult patients having colorectal surgery at least 1 h in length who received both general anesthesia and esophageal core temperature monitoring.

Time weighted average intraoperative core temperature.

Our primary outcome was a composite of serious infections obtained from a surgical registry and billing codes. Average intraoperative esophageal temperatures and the composite of serious 30-day complications were assessed with logistic regression, adjusted for potential confounding factors.

A total of 7908 patients were included in the analysis. A 0.5 °C decrease in time-weighted average intraoperative core temperature ≤ 35.4 °C was associated with an increased odds of serious infection (OR = 1.38, P = .045); that is, hypothermia below 35.4 °C progressively worsened infection risk. Additionally, at higher core temperatures, the odds of serious infection increased slightly with each 0.5 °C increase in average temperature (OR = 1.10, P = .047).

Below 35.5 °C, hypothermia was associated with increased risk of serious infectious complications. Why composite complications increased at higher temperatures remains unclear, but the highest temperatures may reflect febrile patients who had pre-existing infections. Avoiding time-weighted average core temperatures <35.5 °C appears prudent from an infection perspective, but higher temperatures may be needed to prevent other hypothermia-related complications.