Methods of temperature monitoring

By Alex Yartsev - Jan 15, 2016

The collegee's own model answer to Question 8 from the second paper of 2008 offers a pretty good tabulated summary of the various methods of temperature monitoring. Given that brief point-form notes make for the best revision, it would be difficult to justify adding anything extra to such a concise and clear summary.

The key point is that the PA catheter is the gold standard, and everything else is measured against it. The general trend can be described thus: the closer your probe gets to the heart, the more accurate your measurement to the temperature of intracardiac blood.

It would make sense that intracardiac blood should be a good measure of body temperature, as the blood has been circulating all around the body, exchanging heat everywhere. However, not all agree that this is a valid viewpoint. Some have suggested that the better temperature to be guided by is the temperature of the hypothalamus, because it is the organ which is responsible for regulating temperature.

Methods of Measuring Body Temperature in the ICU
	Advantages	Limitations
PAC	Considered gold standard, continuous measurement	Invasive. PAC has a number of serious complications associated with its use
Bladder	Continuous measurement, minimally invasive, stable measurements regardless of urine flow rates Not as accurate as PAC, but better than rectal and surface methods	Costly, needs a monitor for display Source of infection
Rectal probe	Intermittent or continuous measurements	Bacterial metabolism renders the rectum slightly hotter than core temperature Invasive Risk of traumatic insertion Potential source of bacteraemia
Oesophageal	Provide continuous readings Not as accurate as PAC, but better than rectal and surface methods	Position-dependent Risk of oesophageal trauma Uncomfortable
Tympanic	Reflects hypothalamic and core temperature.	Poor agreement with other methods Ear canal obstruction or ear pathology may distort measurements.
Nasopharyngeal	Similar to oesophageal	Risk of sinusitis Contraindicated in base of skull fractures Position-dependent May erroneously measure the temperature fo the humidified gas in the ETT
Oral	safe, convenient, and familiar Accurate - next best thing to the PA catheter	Needs cooperative patients Presence of ET and oro gastric tubes may limit this in ICU patients Mouth breathing, drinking hot or cold fluids may distort measurements.
Forehead	Dot technique, non-invasive	Poor agreement with PAC in ICU patients Intermittent data
Axillary	Non-invasive	Less than core body temperature Intermittent data

References

Giuliano, Karen K., et al. "Temperature measurement in critically ill orally intubated adults: a comparison of pulmonary artery core, tympanic, and oral methods." Critical care medicine 27.10 (1999): 2188-2193.

Lefrant, J-Y., 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 medicine 29.3 (2003): 414-418.

NIERMAN, DAVID M. "Core temperature measurement in the intensive care unit." Critical care medicine 19.6 (1991): 818-823.

WEBB, GEORGE E. "Comparison of esophageal and tympanic temperature monitoring during cardiopulmonary bypass." Anesthesia & Analgesia 52.5 (1973): 729-733.

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