title: An evaluation of a zero-heat-flux cutaneous thermometer in cardiac surgical patients.
abstract: 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.
authors.affiliation: From the Departments of Outcomes Research, General Anesthesiology, Cleveland Clinic, Cleveland, Ohio; Infection Prevention Division, The 3M Company, St. Paul, Minnesota.
authors.forename: Yashar
authors.initials: Y
authors.lastname: Eshraghi
authors.forename: Vivian
authors.initials: V
authors.lastname: Nasr
authors.forename: Ivan
authors.initials: I
authors.lastname: Parra-Sanchez
authors.forename: Albert
authors.initials: A
authors.lastname: Van Duren
authors.forename: Mark
authors.initials: M
authors.lastname: Botham
authors.forename: Thomas
authors.initials: T
authors.lastname: Santoscoy
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Sessler
mesh_terms: D000368:Aged; D015992:Body Mass Index; D006348:Cardiac Surgical Procedures / Q000295:instrumentation / Q000379:methods*; D003627:Data Interpretation, Statistical; D005260:Female; D005546:Forehead; D006801:Humans; D008297:Male; D008875:Middle Aged; D008991:Monitoring, Physiologic; D009765:Obesity / Q000503:physiopathology; D011651:Pulmonary Artery / Q000502:physiology; D012881:Skin Temperature / Q000502:physiology*; D012959:Socioeconomic Factors; D012984:Software; D013821:Thermometers