Measurement of core temperature during postoperative rewarming; a comparison of oesophageal, bladder, and rectal temperatures

Objective: The data of 60 postoperatively sedated and ventilated patients were studied far analysis of oesophageal, bladder, and rectal temperatures. The purpose of the investigation was to clarify whether changes of oesophageal temperature are adequately reflected by bladder and rectal temperatures and whether the rate of rewarming has an influence on the accuracy of the latter two sites. Methods: For temperature recording, a Hi-La Tremp(R) esophageal stethoscope (Mallinckrodt Medical), a Foley FC400-18 catheter temperature sensor (Respiratory Support Products, Mallinckrodt Medical),and a rectal temperature probe N401 (YSI) were used. Each probe and matching recording unit was calibrated over a range of 30-40 degrees C against a reference quartz thermometer (Hewlett packard Model 2801 A) in a thermostated water bath before the investigation, Five measuring points distributed over the whole period of rewarming were evaluated. Patients were assigned to groups with slow and fast rewarming, respectively. Agreement between the methods of measurement was assessed as described by Bland and Altman. Furthermore, differences between the oesophageal and bladder or rectal temperature were checked at: each measuring point for statistical significance using the t-test. Results: In regard to oesophageal temperature,the bladder and pedal temperatures had biases of-0.01 degrees C and -0.03 degrees C, respectively Limits of agreement (+/-2 s) were +/-0.68 degrees C and +/-0.82 degrees C, respectively. The bias of the bladder temperature was independent of the rate of rewarming (Fig. 3). The bias of the rectal temperature, however, differed in regard to the rewarming rate, being +0.06 degrees C in the group with slow rewarming and -0.13 degrees C in the group with fast rewarming (Tables 1 and 2, Fig. 1 and 2). These differences were significant for the measuring points 4 and 5 (Fig. 4). Conclusions: Bladder and rectal temperatures can accurately indicate the oesophageal temperature with a very small bias in postoperatively sedated and ventilated patients. Since the rate of rewarming influences the accuracy of rectal temperature readings, monitoring of bladder temperature seems to be more favourable in the postoperative period.