Temperature measurement - Background

Temperature measurement is a vital sign with a long history, and altered thermoregulation is common in critically ill patients (1).

Historically much of the focus has been on fever and treatment of infection however recent research has turned to hypothermia, both as a negative consequence of disease or as a treatment modality.

Extreme hyperpyrexia
Mild hypothermia
Moderate hypothermia
Mod-deep hypothermia
Deep hypothermia


Core body temperature is defined as the temperature of blood at the hypothalamus or within the core structures of the body. The hypothalamus regulates body temperature by negative feedback mechanisms to:

  1. vasodilate skin vessels in response to temperatures greater than 37⁰C; or
  2. stimulate shivering in response to hypothermia.

Other factors which may affect thermoregulation include diurnal variation, cellular metabolism, exercise, ambient temperature and age (2). Maintenance of temperature within physiological boundaries ensures optimal conditions for enzyme activity and chemical reactions (3).


Current epidemiological evidence suggests that fever holds different risks depending on a patient’s diagnosis. Where patients have an infection the in-hospital risk of death progressively decreases as temperature rises even when temperatures exceed 39⁰C (4). However hyperthermia has been associated with poorer outcomes in patients with traumatic brain injury (5) and intensive care patients who do not have infections (4) or neurological issues (6). Extreme hyperpyrexia (T ≥ 41.5⁰C) represents an emergency that should be treated quickly to avoid organ failure (1). A key problem in understanding the relationship is that studies do not use a universal definition of fever (6).


Negative effects of hypothermia include immunosuppression, electrolyte disorders, insulin resistance, arrhythmias, cold diuresis, hypovolaemia and coagulation (1, 7). Hypothermia has been associated with poorer outcomes in all intensive care patients (4), those with traumatic brain injury (5), post-operative intensive care patients (8) and elderly patients with sepsis (9). Clinicians should endeavour to prevent hypothermia developing as a consequence of exposure or massive blood or fluid resuscitation. Patients should not be warmed faster than 0.5⁰C per hour to avoid localised temperature differences (cerebral thermopooling), cerebral hypoxia and impaired cerebrovascular reactivity (1).

Therapeutic hypothermia (maintaining core temperature between 32-34⁰C) treatment in intensive care has been shown to improve outcomes for patients following cardiac arrest due to ventricular tachycardia or ventricular fibrillation (10) but not for traumatic brain injury (11).

Temperature measurement practices

Accurate identification of body temperature is essential if clinicians are to intervene quickly to prevent the potential negative consequences of abnormal temperatures. However despite long-standing evidence regarding the inaccuracy of surface temperature methods (12-15) they continue to be used in intensive care (16, 17). Additionally, body temperature is an integral component of risk predictor scores for intensive care patients (18) and is used as a diagnostic component for sepsis, systemic inflammatory response syndrome and ventilated associated pneumonia (19). For these reasons guidance regarding temperature measurement is required to ensure the timely and accurate identification of body temperature in critically ill adults.


  1. Faulds M, Meekings T. Temperature management in critically ill patients. Continuing Education in Anaesthesia, Critically Ill and Pain. 2013. Epub 18 January 2013.
  2. Sund-Levander M, Grodzinsky E. Time for a change to assess and evaluate body temperature in clinical practice. International journal of nursing practice. 2009;15(4):241-9.
  3. Hypthamlamic Regulation of Hormonal Functions. 2012. In: Ganong's Review of Medical Physiology [Internet]. The McGraw-Hill Companies. 24.
  4. Young PJ, Saxena M, Beasely R, Bellomo R, Bailey M, Pilcher D, et al. Early peak temperature and mortality in critically ill patients with or without infection. Intensive Care Medicine. 2012;38:437-344. Epub 31 January 2012.
  5. Kim Y. A systematic review of factors contributing to outcomes in patients with traumatic brain injury. Journal of clinical nursing. 2011;20(11-12):1518-32.
  6. Egi M, Morita K. Fever in non-neurological patients: a systematic review of observational studies. Journal of Critical Care. 2012;27(5):428-33.
  7. Polderman KH. Mechanisms of action, physiological effects and complications of hypothermia. Critical care medicine. 2009;37(7):S186-202.
  8. Karalapillai D, Story D, Calzavacca P, Licari E, Liu Y, Hart G. Inadvertent hypothermia and mortality in postoperative intensive care patients: retrospective audit of 5050 patients. Anaesthesia. 2009;64(9):968-72.
  9. Tiruvoipati R, Ong K, Gangopadhyay H, Arora S, CArney I, Botha J. Hypothermia predicts mortality in critically ill patients with sepsis. BMC Geriatrics. 2010;10:70. Epub 16 February 2013.
  10. Arrich J, Holzer M, Havel C, Mullner M, Herkner H. Hypothermia for neuroprotection in adults after cardiopulmonary resuscitation. Cochrane Database of Systematic Reviews. 2012 (9).
  11. Sydenham E, Roberts I, Alderson P. Hypothermia for traumatic brain injury. The Cochrane Collaboration. 2009 (4).
  12. Hooper VD, Andrews JO. Accuracy of noninvasive core temperature measurement in acutely ill adults: the state of the science. Biological Research for Nursing. 2006;8(1):24-34.
  13. Khan T, Vohra H, Paul S, Rosin M, Patel R. Axillary and tympanic membrane temperature measurements are unreliable early after cardiopulmonary bypass. European Journal of Anaesthesiology (EJA). 2006;23(7):551&hyhen.
  14. Giuliano KK, Giuliano AJ, Scott SS, Maclachlan E, Pysznik E, Elliot S, et al. Temperature measurement in critically ill adults: a comparison of typmpanic and oral methods. American Journal of Critical Care. 2000;9:254-61.
  15. Farnell S, Maxwell L, Tan S, Rhodes A, Philips B. Temperature measurement: comparison of non-invasive methods used in adult critical care. Journal of clinical nursing. 2005;14(5):632-9.
  16. Hammond NE, Saxena M, Young P, Taylor. C., Seppelt I, Glass P, et al. Temperature management for patients without brain injury in Australia and New Zealand ICUs: a point prevalence study. Critical Care. 2012;16(supplement 1):p58.
  17. Johnston NJ, King AT, Proteroe R, Child C. Body temperature measurement after severe traumatic brain injury: methods and protocols used in the United Kingdom and Ireland. Resuscitation. 2006;70:254-62.
  18. Zimmerman JE, Kramer AA, McNair DS, Malila GM. Acute physiology and chronic health evaluation (APACHE) IV: hospital mortality assessment for today's critically ill patients. Critical care medicine. 2006;34:1297-310.
  19. CDC. Ventilator-Associated Event (VAE). In: Network NHS, editor. Atlanta: US Government; 2013.


The information on this page is general in nature and cannot reflect individual patient variation. It reflects Australian intensive care practice, which may differ from that in other countries. It is intended as a supplement to the more specific information provided by the doctors and nurses caring for your loved one. ICNSW attests to the accuracy of the information contained here but takes no responsibility for how it may apply to an individual patient. Please refer to the full disclaimer.