Table of Contents  
Year : 2018  |  Volume : 7  |  Issue : 1  |  Page : 28-32

Temperature monitoring in the intensive care unit

Division of Critical Care, Medical ICU, Christian Medical College, Vellore, Tamil Nadu, India

Date of Web Publication1-Feb-2018

Correspondence Address:
Dr. Binila Chacko
Division of Critical Care, Medical ICU, Christian Medical College, Vellore, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijrc.ijrc_13_17

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Close monitoring and management of temperature abnormalities are crucial in the critically ill to minimize the physiological and biochemical ill effects of extremes of temperature. In the intensive care unit, core temperature monitoring using either urinary, nasopharyngeal, or esophageal temperatures is recommended. One needs to be aware of the pitfalls and fallacies of other commonly used sites.

Keywords: Core, methods, nasopharyngeal, esophageal, sites, temperature

How to cite this article:
Chacko B, Peter JV. Temperature monitoring in the intensive care unit. Indian J Respir Care 2018;7:28-32

How to cite this URL:
Chacko B, Peter JV. Temperature monitoring in the intensive care unit. Indian J Respir Care [serial online] 2018 [cited 2020 Aug 10];7:28-32. Available from:

  Temperature Monitoring in Critically Ill Top

Temperature is routinely monitored in all hospitalized patients. In the critically ill, temperature abnormalities [1] and dysregulation have been reported to be frequent,[2] and extremes of temperature have been shown to be associated with poor outcomes.[1] This article reviews the importance of temperature monitoring and describes the methods employed for accurate temperature monitoring in patients in the intensive care unit (ICU).

Is temperature regulation important?

Normally, the temperature is maintained within a narrow range by the thermostat in the hypothalamus. Body temperatures outside this range may result in deleterious effects on biochemical and cellular function. The reported biochemical abnormalities, which include hypokalemia and hypomagnesemia, can impact QT intervals.[3] Severe hyperthermia (>42°C) has effects on oxidative phosphorylation and increases the formation of heat shock proteins. This can subsequently result in a systemic inflammatory response that can progress to multi-organ dysfunction.[4] In the critically ill, where there may be additional metabolic and systemic insults, it would be intuitive to assume that it is important to measure and control temperature accurately to avoid adding insult to injury.

Do temperature abnormalities have an adverse effect on outcomes?

Fever at admission in ICU has been reported in over two-thirds of patients admitted to the ICU, whereas varying grades of hypothermia were reported in close to 20% of patients.[1] The reported effects of fever on outcome are varied ranging from adverse to beneficial. While a meta-analysis by Egi and Morita [5] has suggested that fever may not increase mortality, Circiumaru et al.[2] and Peres Bota et al.[6] reported the reverse. It is hence not clear whether this relationship between fever and mortality reflects an epiphenomenon or a true association. Treatment of fever in the critically ill with antipyretics, however, has not been shown to affect ICU free days.[7],[8]

Recent research has also looked at hypothermia, not only as a negative consequence of disease but also as a treatment modality. In Laupland's study of over 10000 ICU patients,[1] there appeared to be a relationship of hypothermia with outcomes with a mortality of 22%, 38%, and 60%, respectively, in patients manifesting mild (35°C–35.9°C), moderate (32°C–34.9°C), or severe (<32°C) hypothermia. On the other hand, as a treatment modality, therapeutic hypothermia has been reported to have neurobeneficial effect in terms of reducing ischemic reperfusion injury and decreasing excitotoxicity and free-radical production.[9] While earlier studies have shown evidence of improved neurological outcomes with therapeutic hypothermia postcardiac arrest,[10],[11] the most recent evidence [12] found no difference between core temperature targets of 33° versus 36°C. In other scenarios as well, there is insufficient evidence to suggest whether aggressive temperature control will improve outcomes.[7]

The case for accurate temperature monitoring

The high frequency of temperature abnormalities in the critically ill and the reported negative outcome association with extremes of temperature suggest that accurate monitoring of temperature and maintenance of optimal body temperature in the ICU setting is necessary to minimize the physiological and biochemical ill effects of extremes of temperature.

Which temperature should be monitored?

Temperature measurement can either be done as “core” temperature recordings or “peripheral” temperature measurements. Core temperature relates to the “compartment that is composed of highly perfused tissues whose temperature is uniform”[13] and is least affected by environmental influences as opposed to peripheral temperature sites such as the forehead, temporal, or oral, which can be easily affected by the external environment. It has been reported that there is an increase of 1°C for every 4 mm distance from the skin.[14] Given that the site of temperature regulation is the brain, it is assumed that the temperature in normal brain tissue is the gold standard for core temperature monitoring. While it would be ideal to assess core temperature, it may not always be possible, and it is hence important to understand the limitations of the device and the site monitored for clinical decision-making.

When comparing monitored temperature from different sites with the gold standard, most studies have used the definition of a clinically acceptable reflection of the core temperature if it lies within ± 0.3°C.[15],[16] The different methods of temperature monitoring along with their pitfalls and advantages are described in the following section.


Clinical considerations and evidence

The temperature probe should be placed in noninjured tissue. In the absence of intracranial pathology, temperature measured from less invasive sites has reasonably correlated with the temperature in the brain. However, in the presence of brain injury, either traumatic or secondary to stroke, core temperature measurement from other sites have not accurately reflected the temperature in the brain with reported higher brain temperatures in the range of 0.4°C–2.5°C.[17] Given the invasive nature of brain temperature monitoring, there has been research looking at the accuracy of noninvasive brain temperature monitoring by magnetic resonance spectroscopy [18] as of now, this has not yet been validated for regular use.

However, the more important question that needs to be answered is whether the management of “increased” brain temperatures in the setting of intracranial pathology improves neurological outcomes.

As stated earlier, brain temperature has been shown to be higher than other core sites in the setting of brain injury. A recent randomized controlled Eurotherm trial,[7] which looked at the effects of therapeutic hypothermia after traumatic brain injury, found harm in the treatment arm with the study being terminated early due to the adverse effect of therapeutic hypothermia.

Potential pitfalls

This measurement is highly invasive and needs technical expertise to ensure that the temperature probe is placed in noninjured brain tissue.

Pulmonary artery catheter

Clinical considerations and evidence

Temperature monitoring from the pulmonary artery (PA) is also considered as the gold standard for continuous core temperature monitoring since this has been shown to be “closest to the temperature in the high internal jugular vein,”[15],[16],[19] which is the venous drainage of the brain.

Potential pitfalls

While this site has been considered to be the gold standard, this is also invasive and has its share of complications related to catheter insertion and maintenance. In a study on 70 ICU patients, between 20% and 30% had significant adverse events related to the PA catheter.[20] In addition, PA catheter use in the critically ill has not been shown to improve outcomes, and hence, it is not recommended in the intensive care [21] for the routine management of patients or for temperature monitoring.

Urinary catheter

Clinical considerations and evidence

Since hourly urine output monitoring is generally done for all critically ill patients, temperature sensing urinary catheters are increasingly gaining favor in intensive care. A reliable concordance of 0.92 with the PA catheter temperatures,[22] and no added procedural discomfort to the ICU patient are bonuses of this mode of temperature measurement.

In studies that compared bladder and rectal temperatures with PA temperatures, bladder temperatures performed better than rectal temperatures with a higher correlation of 0.78–0.94 as opposed to rectal temperatures where the correlation was 0.49–0.82.[23] Even though urinary thermistors have a lag in sensing rapid changes in core temperature (e.g., cooling during surgery) when compared with esophageal temperature probes, they have been reported to be faster than rectal and skin thermometers at picking up temperature variations.[24]

Potential pitfalls

Although this is not as invasive as the PA catheter, cost and infection are problems that can be associated with this device. In addition, urinary volumes can affect reliability. Better correlation with PA catheter temperatures has been observed in the presence of high urinary volumes (r = 0.90) as compared to low urinary volumes (r = 0.76).[25]


Clinical considerations and evidence

The esophageal probe has to be inserted in the distal third of the esophagus, and its position needs to be confirmed by a chest X-ray.[26] In a study comparing temperatures monitored from the urinary bladder, esophageal, rectal, axillary, and inguinal with the PA temperature, the urinary temperatures, and esophageal temperatures were more reliable [27] than the other sites.

Potential pitfalls

Fluids passing through the nasogastric tubes or nasal breathing may alter the temperature.


Clinical considerations and evidence

The thermocouple needs to be positioned a few centimeter past the nares, and ideally, airflow should be obstructed to prevent air currents from cooling the temperature probe. This also has been shown to have reasonable accuracy with PA temperatures in children [28] and can be used to monitor core temperature.

Potential pitfalls

Airflow can alter the monitored temperature; this hence cannot be used in self-ventilating patients.


Clinical considerations and evidence

Since the tympanic membrane and the hypothalamus share a common blood supply from the internal and external carotids,[29],[30] temperature monitoring from this site has been studied to assess correlation with core temperature.

The thermometer has to be inserted into the external auditory canal after it has been straightened by pulling the pinna in an upward and backward direction. This technique can, however, be compromised in the setting of a tortuous aural canal and obstruction by cerumen.

Potential pitfalls

Pain and tympanic membrane perforation are potential complications of this technique. Furthermore, given the technical issues and the moderate correlation with the core temperature (0.77),[22] tympanic thermometry is not considered to be reliable in critically ill patients.[22],[31]


Clinical considerations and evidence

Traditionally, the rectal route has been used to measure a patient's core temperature. However, it has been found that there is a significant lag of rectal temperature behind other core sites, particularly during rapid temperature changes.[15],[32]

If used, the tip of the temperature probe should be 4 cm in the rectum as the temperature increases by 0.8° for every 2.5 cm.[14],[33],[34]

Potential pitfalls

Rectal perforation and discomfort for the patient are potential risks with this method. Hard feces can impair placement and inflammation and heat-producing microorganisms can affect temperature readings. In addition, rectal temperature has been shown to trail behind core temperature during rapid cooling or warming.[35]


Clinical considerations and evidence

While this site of temperature measurement is commonly used, concordance with core temperature is only moderate with variability of 0.27°C ± 0.45°C.[27],[36],[37]

The thermometer must be kept in the axilla for the appropriate duration. There are different types of axillary digital thermometers available for use. One thermometer gives a quick calculated temperature value (within 30 s to 1 min); this could be one of the factors that adds to poor reliability. There are other electronic thermometers that need to be kept in the axilla for 5 min; this may be more reflective of the core temperature. By tradition, to derive core temperatures from oral and axillary temperature readings 0.3 and 0.5°C is added to the measured value, respectively. This, however, has no scientific basis and is not evidence-based! In fact no factor exists at this point of time that allows accurate estimation of temperature at one site from monitored temperature at another site.

Potential pitfalls

This does not allow continuous temperature recording, and furthermore, ambient temperature, local blood flow, and sweat can affect accuracy of the monitored temperature. It is hence not recommended for temperature monitoring in the critically ill.

[Table 1] summarizes the various methods of temperature assessment, clinical considerations, potential pitfalls, and the evidence for the use of different methods of temperature recording.
Table 1: Sites of temperature recording with pitfalls and evidence

Click here to view

How often should temperature be monitored?

It is recommended that critically ill unstable patients have continuous invasive temperature monitoring using either urinary catheter or esophageal temperature probes.[38] Specific situations in ICU where continuous temperature recording is advised are during targeted temperature management postcardiac arrest or during cooling or rewarming for extremes of temperature. This can help pick up “after-drop,”[39] which is a drop in the core temperature during rewarming of a hypothermic patient (accidental or therapeutically induced hypothermia) when cold blood is shunted to the core.

In the other hospital wards and the stable critically ill patient, it is reasonable to measure axillary temperature with the appropriate thermometer every 4–6 h.[38]

Which temperature-measuring device should be used?

The temperature measuring devices can be either nonelectrical devices, electrical devices, infrared devices or single of multi-use chemical thermometers.[13]

  1. Nonelectrical devices – These contain either mercury or alcohol. Mercury thermometers are now not used given the time needed for calibration and the problems with mercury spill. Alcohol thermometers are only suitable for lower temperatures since alcohol boils at 78.5°C
  2. Electrical devices – These use thermistors, thermocouples, or resistance thermometers. PA, esophageal, nasopharyngeal, and bladder temperature monitors use thermistors. Even though thermistors need calibration, they have better accuracy and precision than thermocouples. Resistance thermometers are not very sensitive and are based on the principle that the resistance of the metal increases with increase in temperature
  3. Infrared devices – This technology, used in tympanic thermometers, work on the principle that radiation (heat) is converted into an electrical signal. These devices, even though widely popular, do not reliably reflect core temperatures
  4. Single- or multi-use chemical thermometers have some accuracy issues for clinical use [40] and are hence not recommended.

In ICUs, electrical devices using thermistors are recommended for the reasons documented above.

  Conclusions Top

It is important to closely monitor, manipulate, and regulate temperature in the critically ill to minimize the physiological and biochemical ill-effects of extremes of temperature. In the ICU, based on the evidence provided above, core temperature monitoring using either urinary, nasopharyngeal, or esophageal temperatures is recommended. One needs to be aware of the pitfalls and fallacies of other commonly used sites.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Laupland KB, Zahar JR, Adrie C, Schwebel C, Goldgran-Toledano D, Azoulay E, et al. Determinants of temperature abnormalities and influence on outcome of critical illness. Crit Care Med 2012;40:145-51.  Back to cited text no. 1
Circiumaru B, Baldock G, Cohen J. A prospective study of fever in the Intensive Care Unit. Intensive Care Med 1999;25:668-73.  Back to cited text no. 2
Tokutomi T, Miyagi T, Morimoto K, Karukaya T, Shigemori M. Effect of hypothermia on serum electrolyte, inflammation, coagulation, and nutritional parameters in patients with severe traumatic brain injury. Neurocrit Care 2004;1:171-82.  Back to cited text no. 3
Leon LR, Helwig BG. Heat stroke: Role of the systemic inflammatory response. J Appl Physiol (1985) 2010;109:1980-8.  Back to cited text no. 4
Egi M, Morita K. Fever in non-neurological critically ill patients: A systematic review of observational studies. J Crit Care 2012;27:428-33.  Back to cited text no. 5
Peres Bota D, Lopes Ferreira F, Mélot C, Vincent JL. Body temperature alterations in the critically ill. Intensive Care Med 2004;30:811-6.  Back to cited text no. 6
Andrews PJ, Sinclair HL, Rodriguez A, Harris BA, Battison CG, Rhodes JK, et al. Hypothermia for intracranial hypertension after traumatic brain injury. N Engl J Med 2015;373:2403-12.  Back to cited text no. 7
Drewry AM, Ablordeppey EA, Murray ET, Stoll CRT, Izadi SR, Dalton CM, et al. Antipyretic therapy in critically ill septic patients: A Systematic review and meta-analysis. Crit Care Med 2017;45:806-13.  Back to cited text no. 8
González-Ibarra FP, Varon J, López-Meza EG. Therapeutic hypothermia: Critical review of the molecular mechanisms of action. Front Neurol 2011;2:4.  Back to cited text no. 9
Bernard SA, Gray TW, Buist MD, Jones BM, Silvester W, Gutteridge G, et al. Treatment of comatose survivors of out-of-hospital cardiac arrest with induced hypothermia. N Engl J Med 2002;346:557-63.  Back to cited text no. 10
Hypothermia after Cardiac Arrest Study Group. Mild therapeutic hypothermia to improve the neurologic outcome after cardiac arrest. N Engl J Med 2002;346:549-56.  Back to cited text no. 11
Nielsen N, Wetterslev J, Cronberg T, Erlinge D, Gasche Y, Hassager C, et al. Targeted temperature management at 33°C versus 36°C after cardiac arrest. N Engl J Med 2013;369:2197-206.  Back to cited text no. 12
Sessler DI. Temperature monitoring and perioperative thermoregulation. Anesthesiology 2008;109:318-38.  Back to cited text no. 13
Sund-Levander M, Grodzinsky E. Time for a change to assess and evaluate body temperature in clinical practice. Int J Nurs Pract 2009;15:241-9.  Back to cited text no. 14
Robinson J, Charlton J, Seal R, Spady D, Joffres MR. Oesophageal, rectal, axillary, tympanic and pulmonary artery temperatures during cardiac surgery. Can J Anaesth 1998;45:317-23.  Back to cited text no. 15
Giuliano KK, Scott SS, Elliot S, Giuliano AJ. Temperature measurement in critically ill orally intubated adults: A comparison of pulmonary artery core, tympanic, and oral methods. Crit Care Med 1999;27:2188-93.  Back to cited text no. 16
Mcilvoy L. Comparison of brain temperature to core temperature: A review of the literature. J Neurosci Nurs 2004;36:23-31.  Back to cited text no. 17
Karaszewski B, Wardlaw JM, Marshall I, Cvoro V, Wartolowska K, Haga K, et al. Measurement of brain temperature with magnetic resonance spectroscopy in acute ischemic stroke. Ann Neurol 2006;60:438-46.  Back to cited text no. 18
Eichna LW, Berger AR, Rader B, Becker WH. Comparison of intracardiac and intravascular temperatures with rectal temperatures in man. J Clin Invest 1951;30:353-59.  Back to cited text no. 19
Fein AM, Goldberg SK, Walkenstein MD, Dershaw B, Braitman L, Lippmann ML, et al. Is pulmonary artery catheterization necessary for the diagnosis of pulmonary edema? Am Rev Respir Dis 1984;129:1006-9.  Back to cited text no. 20
Harvey S, Young D, Brampton W, Cooper AB, Doig G, Sibbald W, et al. Pulmonary artery catheters for adult patients in intensive care. Cochrane Database Syst Rev 2006;(3):CD003408.  Back to cited text no. 21
Moran JL, Peter JV, Solomon PJ, Grealy B, Smith T, Ashforth W, et al. Tympanic temperature measurements: Are they reliable in the critically ill? A clinical study of measures of agreement. Crit Care Med 2007;35:155-64.  Back to cited text no. 22
Mravinac CM, Dracup K, Clochesy JM. Urinary bladder and rectal temperature monitoring during clinical hypothermia. Nurs Res 1989;38:73-6.  Back to cited text no. 23
Fallis WM. Monitoring urinary bladder temperature in the Intensive Care Unit: State of the science. Am J Crit Care 2002;11:38-45.  Back to cited text no. 24
Sato H, Yamakage M, Okuyama K, Imai Y, Iwashita H, Ishiyama T, et al. Urinary bladder and oesophageal temperatures correlate better in patients with high rather than low urinary flow rates during non-cardiac surgery. Eur J Anaesthesiol 2008;25:805-9.  Back to cited text no. 25
Whitby JD, Dunkin LJ. Temperature differences in the oesophagus. Preliminary study. Br J Anaesth 1968;40:991-5.  Back to cited text no. 26
Lefrant JY, Muller L, de La Coussaye JE, Benbabaali M, Lebris C, Zeitoun N, et al. Temperature measurement in intensive care patients: Comparison of urinary bladder, oesophageal, rectal, axillary, and inguinal methods versus pulmonary artery core method. Intensive Care Med 2003;29:414-8.  Back to cited text no. 27
Maxton FJ, Justin L, Gillies D. Estimating core temperature in infants and children after cardiac surgery: A comparison of six methods. J Adv Nurs 2004;45:214-22.  Back to cited text no. 28
Benzinger M. Tympanic thermometry in surgery and anesthesia. JAMA 1969;209:1207-11.  Back to cited text no. 29
Giuliano KK, Giuliano AJ, Scott SS, MacLachlan E, Pysznik E, Elliot S, et al. Temperature measurement in critically ill adults: A comparison of tympanic and oral methods. Am J Crit Care 2000;9:254-61.  Back to cited text no. 30
Stavem K, Saxholm H, Smith-Erichsen N. Accuracy of infrared ear thermometry in adult patients. Intensive Care Med 1997;23:100-5.  Back to cited text no. 31
Molnar GW, Read RC. Studies during open-heart surgery on the special characteristics of rectal temperature. J Appl Physiol 1974;36:333-6.  Back to cited text no. 32
Togawa T. Body temperature measurement. Clin Phys Physiol Meas 1985;6:83-108.  Back to cited text no. 33
Rotello LC, Crawford L, Terndrup TE. Comparison of infrared ear thermometer derived and equilibrated rectal temperatures in estimating pulmonary artery temperatures. Crit Care Med 1996;24:1501-6.  Back to cited text no. 34
Ash CJ, Cook JR, McMurry TA, Auner CR. The use of rectal temperature to monitor heat stroke. Mo Med 1992;89:283-8.  Back to cited text no. 35
Hissink Muller PC, van Berkel LH, de Beaufort AJ. Axillary and rectal temperature measurements poorly agree in newborn infants. Neonatology 2008;94:31-4.  Back to cited text no. 36
Falzon A, Grech V, Caruana B, Magro A, Attard-Montalto S. How reliable is axillary temperature measurement? Acta Paediatr 2003;92:309-13.  Back to cited text no. 37
Temperature Measurement for Critically ill Adults a Clinical Practice Guideline; 2014. p. 1-30. Available from: [Last accessed on 2017 Nov 20].  Back to cited text no. 38
Webb P. Afterdrop of body temperature during rewarming: An alternative explanation. J Appl Physiol (1985) 1986;60:385-90.  Back to cited text no. 39
Fallis WM, Hamelin K, Wang X, Symonds J. A multimethod approach to evaluate chemical dot thermometers for oral temperature measurement. J Nurs Meas 2006;14:151-62.  Back to cited text no. 40


  [Table 1]

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