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An Evaluation of a Zero-Heat-Flux Cutaneous Thermometer in Cardiac Surgical Patients

Eshraghi, Yashar MD*; Nasr, Vivian MD*†; Parra-Sanchez, Ivan MD*†; Van Duren, Albert MS§; Botham, Mark MD*†; Santoscoy, Thomas MD*†; Sessler, Daniel I. MD*

doi: 10.1213/ANE.0000000000000319
Cardiovascular Anesthesiology: Research Report

BACKGROUND: Although core temperature can be measured invasively, there are currently no widely available, reliable, noninvasive thermometers for its measurement. We thus compared a prototype zero-heat-flux thermometer with simultaneous measurements from a pulmonary artery catheter. Specifically, we tested the hypothesis that zero-heat-flux temperatures are sufficiently accurate for routine clinical use.

METHODS: Core temperature was measured from the thermistor of a standard pulmonary artery catheter and with a prototype zero-heat-flux deep-tissue thermometer in 105 patients having nonemergent cardiac surgery. Zero-heat-flux probes were positioned on the lateral forehead and lateral neck. Skin surface temperature probes were attached to the forehead just adjacent to the zero-heat-flux probe. Temperatures were recorded at 1-minute intervals, excluding the period of cardiopulmonary bypass, and for the first 4 postoperative hours. Zero-heat-flux and pulmonary artery temperatures were compared with bias analysis; differences exceeding 0.5°C were considered to be potentially clinically important.

RESULTS: The mean duration in the operating room was 279 ± 75 minutes, and the mean cross-clamp time was 118 ± 50 minutes. All subjects were monitored for an additional 4 hours in the intensive care unit. The average overall difference between forehead zero-heat-flux and pulmonary artery temperatures (i.e., forehead minus pulmonary artery) was −0.23°C (95% limits of agreement of ±0.82); 78% of the differences were ≤0.5°C. The average intraoperative temperature difference was −0.08°C (95% limits of agreement of ±0.88); 84% of the differences were ≤0.5°C. The average postoperative difference was −0.32°C (95% limits of agreement of ±0.75); 84% of the differences were ≤0.5°C. Bias and precision values for neck site were similar to the forehead values. Uncorrected forehead skin temperature showed an increasing negative bias as core temperature decreased.

CONCLUSIONS: Core temperature can be noninvasively measured using the zero-heat-flux method. Bias was small, but precision was slightly worse than our designated 0.5°C limits compared with measurements from a pulmonary artery catheter.

Published ahead of print July 18, 2014.

From the Departments of *Outcomes Research, General Anesthesiology, Cleveland Clinic, Cleveland, Ohio; §Infection Prevention Division, The 3M Company, St. Paul, Minnesota.

Published ahead of print July 18, 2014.

Yashar Eshraghi, MD, is currently affiliated with the Department of Anesthesiology, Case Western Reserve University, Metrohealth Medical Center, Cleveland, Ohio.

Accepted for publication April 28, 2014.

Funding: Supported by 3M. Dr. Sessler serves on two 3M advisory boards; all fees are donated to charity. Dr. Sessler’s department conducts sponsored trials for 3M and other companies that manufacture temperature monitoring and measurements systems. None of the authors has a personal financial interest in this work.

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

Reprints will not be available from the authors.

Address correspondence to Daniel I. Sessler, MD, Department of Outcomes Research, Cleveland Clinic, 9500 Euclid Avenue, P77, Cleveland, OH 44195. Address e-mail to On the world wide web:

© 2014 International Anesthesia Research Society