Heating and Cooling Rates With an Esophageal Heat Exchange System

Abstract

Background: The Esophageal Cooling Device circulates warm or cool water through an esophageal heat exchanger, but warming and cooling efficacy in patients remains unknown. We therefore determined heat exchange rates during warming and cooling.

Methods: Nineteen patients completed the trial. All had general endotracheal anesthesia for nonthoracic surgery. Intraoperative heat transfer was measured during cooling (exchanger fluid at 7°C) and warming (fluid at 42°C). Each was evaluated for 30 minutes, with the initial condition determined randomly, starting at least 40 minutes after induction of anesthesia. Heat transfer rate was estimated from fluid flow through the esophageal heat exchanger and inflow and outflow temperatures. Core temperature was estimated from a zero-heat-flux thermometer positioned on the forehead.

Results: Mean heat transfer rate during warming was 18 (95% confidence interval, 16-20) W, which increased core temperature at a rate of 0.5°C/h ± 0.6°C/h (mean ± standard deviation). During cooling, mean heat transfer rate was -53 (-59 to -48) W, which decreased core temperature at a rate of 0.9°C/h ± 0.9°C/h.

Conclusions: Esophageal warming transferred 18 W which is considerably less than the 80 W reported with lower or upper body forced-air covers. However, esophageal warming can be used to supplement surface warming or provide warming in cases not amenable to surface warming. Esophageal cooling transferred more than twice as much heat as warming, consequent to the much larger difference between core and circulating fluid temperature with cooling (29°C) than warming (6°C). Esophageal cooling extracts less heat than endovascular catheters but can be used to supplement catheter-based cooling or possibly replace them in appropriate patients.

Conflict of interest statement

Conflicts of Interest: See Disclosures at the end of the article.

Figures

Figure 1.

The heat exchanging tube. The outer tubes are connected to a Gaymar Medi-Therm III circulating water system.

Figure 2.

Study flow diagram.

Figure 3.

Heat transfer during cooling. Mean heat transfer over 30 min was −53 (95% confidence interval, −59 to −48) W. The middle, upper, and lower edges of the boxplot indicate the 50th, 75th, and 25th percentiles, respectively. The ends of the vertical lines indicate 1.5 times the interquartile range. The cross inside the boxplot is the mean.

Figure 4.

Heat transfer during warming. Mean heat transfer over 30 min was 18 (95% confidence interval, 16–20) W. The middle, upper, and lower edges of the boxplot indicate the 50th, 75th, and 25th percentiles, respectively. The ends of the vertical lines indicate 1.5 times the interquartile range. The cross inside the boxplot is the mean.

Figure 5.

Raw temperature. Each line represents individual temperature change for 19 patients. The middle, upper, and lower edges of the boxplot indicate the 50th, 75th, and 25th percentiles, respectively. The ends of the vertical lines indicate 1.5 times the interquartile range. The cross inside the boxplot indicates a mean temperature. A, Two boxplots of core temperature estimated from a zero-heat-flux thermometer on the forehead before and after 30-min cooling with Esophageal Cooling Device with a middle plot of individual patients temperature change. During cooling, initial core temperature was 35.7°C ± 0.6°C, decreasing to 35.3°C ± 0.6°C over 30 min. The mean cooling rate was thus 0.9°C/h ± 0.9°C/h, which was statistically significant (P < .001). B, Two boxplots of core temperature before and after 30-min warming with Esophageal Cooling Device with a middle plot of individual patients temperature change. Initial core temperature during warming averaged 35.5°C ± 0.5°C (SD), increasing to 35.8°C ± 0.6°C over 30 min. The mean warming rate was thus 0.5°C/h ± 0.6°C/h, which was a significant change (paired t test P = .001). SD indicates standard deviation.