Intraoperative core temperature patterns, transfusion requirement, and hospital duration in patients warmed with forced air

Abstract

Background: Core temperature patterns in patients warmed with forced air remain poorly characterized. Also unknown is the extent to which transient and mild intraoperative hypothermia contributes to adverse outcomes in broad populations.

Methods: We evaluated esophageal (core) temperatures in 58,814 adults having surgery lasting >60 min who were warmed with forced air. Independent associations between hypothermic exposure and transfusion requirement and duration of hospitalization were evaluated.

Results: In every percentile subgroup, core temperature decreased during the first hour and subsequently increased. The mean lowest core temperature during the first hour was 35.7 ± 0.6°C. Sixty-four percent of the patients reached a core temperature threshold of <36°C 45 min after induction; 29% reached a core temperature threshold of <35.5°C. Nearly half the patients had continuous core temperatures <36°C for more than an hour, and 20% of the patients were <35.5°C for more than an hour. Twenty percent of patients had continuous core temperatures <36°C for more than 2 h, and 8% of the patients were below 35.5°C for more than 2 h. Hypothermia was independently associated with both transfusions and duration of hospitalization, although the prolongation of hospitalization was small.

Conclusions: Even in actively warmed patients, hypothermia is routine during the first hour of anesthesia. Thereafter, average core temperatures progressively increase. Nonetheless, intraoperative hypothermia was common, and often prolonged. Hypothermia was associated with increased transfusion requirement, which is consistent with numerous randomized trials.

Fig. 1

Flow chart indicating the artifact removal algorithm for intraoperative core temperature measurements.

Fig. 2

Study flow diagram.

Fig. 3

Distribution of core temperature as a function of time after induction among 58,814 patients.

Fig. 4

Incidence of hypothermia as a function of time after induction, under progressive core temperature thresholds defining hypothermia.

Fig. 5

Incidence of (any) hypothermic episodes during the case, according to progressive core temperature thresholds defining hypothermia.

Fig. 6

Adjusted probability of transfusion estimates versus integrated area above the core-temperature-versus-time curve and below a threshold of 37°C, Estimates adjusted to an “at risk” reference population defined by age >55 yr, body mass index <25 kg/m², preoperative hemoglobin <1.4 g/dL, and duration of surgery >4 h. Shaded regions represent pointwise, Bonferroni-adjusted (for simultaneous analysis on two outcomes) 95% confidence intervals. Regression model based on 45,866 patients who were admitted on the day of surgery and who had esophageal temperature monitoring. *adjusted for year, type, and duration of surgery, body mass index, age, preoperative platelet count, preoperative hemoglobin, estimated blood loss, and individual anesthesiologist, as well as the Elixhauser comorbidities (see table 2 for a listing of these comorbidities). Pr = probability.

Fig. 7

Adjusted estimates of geometric mean duration of hospitalization versus integrated area above the core-temperature-versus-time curve and below a threshold of 37°C, for 39,180 hospital in-patients who were admitted on the day of surgery and who had intraoperative esophageal temperature monitoring. Shaded regions represent pointwise, Bonferroni-adjusted (for simultaneous analysis on two outcomes) 95% confidence intervals. *adjusted for year, type, and duration of surgery, body mass index, age, preoperative platelet count, preoperative hemoglobin, estimated blood loss, and individual anesthesiologist, as well as the Elixhauser comorbidities (see table 2 for a listing of these comorbidities). LOS = length of stay.