Forced-air warming and continuous core temperature monitoring with zero-heat-flux thermometry during cesarean section: a retrospective observational cohort study

Abstract

Background: Over 30% of parturients undergoing spinal anesthesia for cesarean section become intraoperatively hypothermic. This study assessed the magnitude of hypothermic insult in parturients and newborns using continuous, high-resolution thermometry and evaluated the efficiency of intraoperative forced-air warming for prevention of hypothermia.

Methods: One hundred and eleven parturients admitted for elective or emergency cesarean section under spinal anesthesia with newborn bonding over a 5-month period were included in this retrospective observational cohort study. Patients were divided into two groups: the passive insulation group, who received no active warming, and the active warming group, who received convective warming through an underbody blanket. Core body temperature was continuously monitored by zero-heat-flux thermometry and automatically recorded by data-loggers. The primary outcome was the incidence of hypothermia in the operating and recovery room. Neonatal outcomes were also analyzed.

Results: The patients in the passive insulation group had significantly lower temperatures in the operating room compared to the actively warmed group (36.4°C vs. 36.6°C, p = 0.005), including temperature at skin closure (36.5°C vs. 36.7°C, p = 0.017). The temperature of the newborns after discharge from the postanesthetic care unit was lower in the passive insulation group (36.7°C vs. 37.0°C, p = 0.002); thirteen (15%) of the newborns were hypothermic, compared to three (4%) in the active warming group (p < 0.01).

Conclusion: Forced-air warming decreases perioperative hypothermia in parturients undergoing cesarean section but does not entirely prevent hypothermia in newborns while bonding. Therefore, it can be effectively used for cesarean section, but special attention should be given to neonates.

Keywords: Cesarean section; Core temperature; Hypothermia; Newborn bonding; Zero-heat-flux.

Figure 1

Flow Diagram of the study based on the STROBE Statement. Explanatory footnote: CS, cesarean section; PDA, peridural anesthesia; SpA, spinal anesthesia; PI, passive insulation; AW, active warming. ^a Data were considered valid if temperature monitoring was started prior to induction of anesthesia and the calibration of the ZHF sensor was completed.

Figure 2

Maternal core temperature. Explanatory footnote: Values are presented as the mean and the whiskers are SD. Time 0 represents onset of spinal anesthesia; continuous red line: active warming (AW) group; continuous blue line: passive insulation (PI) group; *: statistically significant differences AW group vs. PI group (p < 0.05).

Figure 3

Probability to recover from hypothermia. Explanatory footnote: Kaplan-Meier curve showing the probability to recover from hypothermia to 90% of the baseline temperature. Differences are statistically significant (p < 0.001). Time 0: nadir of temperature, defined as the lowest recorded temperature during the observation time; continuous red line: active warming (AW) group; continuous blue line: passive insulation (PI) group; right censored data represented by “ | “.

Figure 4

Newborn core temperature. Explanatory footnote: Box and whisker plot of newborns core temperature. No statistically significant difference at birth (p = 0.67); statistically significant difference (p = 0.002) at discharge from the postanesthetic care unit (PACU). Boxes indicate the lower and upper quartile. Horizontal line in each box represents the median temperature. Vertical lines represent the minimum and maximum recorded temperatures. The dot outside the boxes represents mean temperature outside the expected distribution. Red boxes: active warming group; blue boxes: passive insulation group.