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

  • James M. Jack
  • Helen Ellicott
  • Christopher I. Jones
  • Stephen A. Bremner
  • Ian Densham
  • C. Mark Harper
Original Research


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™ Temperature Monitoring System Zero Flux Thermometer and the CorTempR™ 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 °C, with 95% limits of agreement − 2.4 °C to 3.2 °C. 75.4% of readings were within ± 0.5 °C of the OTP reading. The bias for the zero flux electrode compared to oesophageal probe was + 0.02 °C with 95% limits of agreement − 0.5 °C to 0.5 °C. 97.7% of readings were within ± 0.5 °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.

Trial registration The study was registered at, NCT Number: NCT02121574.


Temperature measurement Perioperative Thermometry Anaesthesia 



The authors wish to thank David Crook PhD for assistance with study design.


This study was funded by a small project grant from the Association of Anaesthetists of Great Britain and Ireland Foundation, administered by the National Institute for Academic Anaesthesia (WKR0-2013-0051).

Compliance with ethical standards

Conflict of interest

C.M.H. has received loans of equipment from various manufacturers of warming devices, including Inditherm, Augustine Biomedical, Arizant, 3M and Mölnlycke. He has also received expenses and honoraria for sitting on advisory boards for 3M and Mölnlycke. Other authors declare that they have no conflict of interest.


  1. 1.
    Harper CM, Andrzejowski JC, Alexander R. NICE and warm. Br J Anaesth. 2008;101(3):293–95. Scholar
  2. 2.
    Harper CM, McNicholas T, Gowrie-Mohan S. Maintaining perioperative normothermia. Brit Med J. 2003;326(7392):721–2.CrossRefGoogle Scholar
  3. 3.
    Sessler DI. Perioperative heat balance. Anesthesiology. 2000;92(2):578–96.CrossRefGoogle Scholar
  4. 4.
    NICE. Hypothermia: prevention and management in adults having surgery. NICE clinical guideline 65. London: National Institute for Health and Clinical Excellence; 2008 (updated 2016).Google Scholar
  5. 5.
    Sessler D. Temperature monitoring and perioperative thermoregulation. Anesthesiology. 2008;109(2):318–38.CrossRefGoogle Scholar
  6. 6.
    Harper CM. The need for an accurate noninvasive thermometer. Anesth Analg. 2009;109(1):288.CrossRefGoogle Scholar
  7. 7.
    Fox RH, Solman AJ, Isaacs R, et al. A new method for monitoring deep body temperature from the skin surface. Clin Sci. 1973;44:81–6.CrossRefGoogle Scholar
  8. 8.
    Teunissen LP, Klewer J, de Haan A, et al. Noninvasive continuous core temperature measurement by zero heat flux. Physiol Meas. 2011;32:559–70.CrossRefGoogle Scholar
  9. 9.
    Wang M, Singh A, Qureshi H, et al. Optimal depth for nasopharyngeal temperature probe positioning. Anesth Analg. 2016;122(5):1434–8. Scholar
  10. 10.
    Bland JM, Altman DG. Agreement between methods of measurement with multiple observations per individual. J Biopharm Stat. 2007;17(4):571–82. Scholar
  11. 11.
    Clinical measurement and assessing agreement. Curr Anaesth Crit Care 2008; 19 (5–6): 328–9. Scholar
  12. 12.
    Lancaster GA, Dodd S, Williamson PR. Design and analysis of pilot studies: recommendations for good practice. J Eval Clin Pract. 2004;10(2):307–12.CrossRefGoogle Scholar
  13. 13.
    Lees DE, Kim YD, Macnamara TE. Noninvasive determination of core temperature during anesthesia. South Med J. 1980;73(10):1322–24.CrossRefGoogle Scholar
  14. 14.
    Kimberger O, Thell R, Schuh M, et al. Accuracy and precision of a novel non-invasive core thermometer. Br J Anaesth. 2009;103(2):226–31. Scholar
  15. 15.
    Eshraghi Y, Nasr V, Parra-Sanchez I, et al. An evaluation of a zero-heat-flux cutaneous thermometer in cardiac surgical patients. Anesth Analg. 2014;119(3):543–49. Scholar
  16. 16.
    Iden T, Horn E-P, Bein B, et al. Intraoperative temperature monitoring with zero heat flux technology (3M SpotOn sensor) in comparison with sublingual and nasopharyngeal temperature: an observational study. Eur J Anaesthesiol. 2015;32(6):387–91. Scholar
  17. 17.
    Mäkinen M-T, Pesonen A, Jousela I, et al. Novel zero-heat-flux deep body temperature measurement in lower extremity vascular and cardiac surgery. J Cardiothorac Vasc Anesth. 2016;30(4):973–8.CrossRefGoogle Scholar
  18. 18.
    Sastre JA, Pascual MJ, López T. Evaluation of the novel non-invasive zero-heat-flux Tcore™ thermometer in cardiac surgical patients. J Clin Monit Comput. 2018. Scholar
  19. 19.
    Eshraghi Y, Nasr V, Parra-Sanchez I, et al. An evaluation of a zero-heat-flux cutaneous thermometer in cardiac surgical patients. Anesth Analg. 2014;119:543–9.CrossRefGoogle Scholar
  20. 20.
    Darwent D, Zhou X, Heuvel C, et al. The validity of temperature-sensitive ingestible capsules for measuring core body temperature in laboratory protocols. Chronobiol Int. 2011;28(8):719–26. Scholar
  21. 21.
    Byrne C, Lim CL. The ingestible telemetric body core temperature sensor: a review of validity and exercise applications. Br J Sports Med. 2007;41(3):126–33. Scholar
  22. 22.
    Aughey RJ, Goodman CA, McKenna MJ. Greater chance of high core temperatures with modified pacing strategy during team sport in the heat. J Sci Med Sport. 2014;17(1):113–18. Scholar
  23. 23.
    Hadian M, Pinsky MR. Evidence-based review of the use of the pulmonary artery catheter: impact data and complications. Crit Care. 2006;10(3):1–11. Scholar

Copyright information

© Springer Nature B.V. 2019

Authors and Affiliations

  1. 1.Brighton and Sussex University Hospitals Trust, Royal Sussex County HospitalBrightonUK
  2. 2.Department of Primary Care and Public Health, Brighton and Sussex Medical SchoolUniversity of BrightonBrightonUK

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