Association between postoperative body temperature and in-hospital mortality: a nationwide cohort study of 157,028 critically ill patients in Japan.

Purpose: The association between postoperative body temperature and in-hospital mortality remains unclear. We sought to evaluate this association across all surgical patients and assessed whether it is affected by the indication for surgery (i.e., surgical source control of infection vs other indications).

Methods: In a nationwide cohort study, we included critically ill adult patients registered in the Japanese Intensive Care Patient Database who underwent surgery between 2015 and 2021. We evaluated whether the body temperature was associated with in-hospital mortality, and if a differential effect was observed in patients who underwent surgery for source control of infection vs other indications (control group). We categorized the highest body temperatures recorded in the 24 hr after admission following surgery in 0.5-°C intervals and evaluated them using multivariable regression. We conducted a subgroup analysis of patients who underwent surgery for infection control vs other indications. We report the summary estimates using adjusted odds ratios (ORs) and 95% confidence intervals (CIs). We examined the association between body temperature category and in-hospital mortality using cubic spline models to assess nonlinear associations.

Results: Among 157,028 patients, the overall in-hospital mortality was 2.9%. We observed a U-shaped association of temperature and mortality, with increased mortality at body temperatures < 36.0 °C (OR, 2.15; 95% CI, 1.62 to 2.86) and > 40.0 °C (OR, 1.41; 95% CI, 1.02 to 1.96). We observed the lowest mortality at 37.5-37.9 °C (OR, 0.62; 95% CI, 0.55 to 0.70). Low body temperatures were associated with increased mortality regardless of the presence or absence of infection, while high body temperatures were not associated with increased mortality in patients undergoing surgery for source control of infection.

Conclusions: In this large nationwide cohort of critically ill surgical patients in Japan, we observed that low and high postoperative body temperatures were associated with increased in-hospital mortality. Nevertheless, we did not observe the association with high body temperature and increased mortality in the subgroup of patients having undergone surgery for infection control.