Determining the accuracy of zero-flux and ingestible thermometers in the peri-operative setting

Accurately monitoring peri-operative core temperature is a cornerstone of good practice. Relatively invasive devices such as oesophageal temperature probes and pulmonary artery catheters facilitate this, but are inappropriate for many patients. There remains a need for accurate monitors of core temperature that can be used in awake patients. This study compared the accuracy of two core temperature thermometers that can be used for this purpose: the 3M Bair Hugger (TM) Temperature Monitoring System Zero Flux Thermometer and the CorTempR (TM) Wireless Ingestible Temperature Sensor. Readings were compared with the oesophageal probe, the current intraoperative standard. Thirty patients undergoing elective surgical procedures under general anaesthesia were recruited. The ingestible sensor was ingested prior to induction of anaethesia, and post induction, the zero-flux electrode attached above the right eyebrow and oesophageal probe inserted. During surgery, the temperature on each device was recorded every minute. Measurements were compared using Bland-Altman analysis. The ingestible sensor experienced interference from use of diathermy and fluoroscopy in the operating theatre, rendering 39% of its readings unusable. These were removed from analysis. With remaining readings the bias compared with oesophageal probe was + 0.42 degrees C, with 95% limits of agreement - 2.4 degrees C to 3.2 degrees C. 75.4% of readings were within +/- 0.5 degrees C of the OTP reading. The bias for the zero flux electrode compared to oesophageal probe was + 0.02 degrees C with 95% limits of agreement - 0.5 degrees C to 0.5 degrees C. 97.7% of readings were within +/- 0.5 degrees C of the oesophageal probe. The study findings suggest the zero-flux thermometer is sufficiently accurate for clinical use, whereas the ingestible sensor is not.