Question 8

Highest mark

Outline the advantages and limitations of the various sites for measuring body temperature in critically ill patients.

(You may tabulate your answer).

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College Answer

	Advantages	Limitations
PAC	Considered gold standard, continuous measurement	Invasive, needs a PA catheter
Bladder	Continuous measurement, minimally invasive, stable measurements regardless of urine flow rates	Costly, needs a monitor for display.
Rectal probe	Intermittent or continuous measurements	Few tenths of a degree higher than core temperature, intrusive, may be difficult with patient positioning in ICU, risk of spread of pathogens, rectal trauma
Oesophageal	Provide continuous readings	Probe position difficult to confirm as they are not always radio-opaque, risk of oesophageal trauma or perforation, uncomfortable in spontaneous or alert breathing patients
Tympanic	Reflects hypothalamic and core temperature.	Poor agreement with other methods, presence of wax or ear pathology may distort measurements.
Nasopharyngeal	Similar to oesophageal	Sinusitis, can’t be used in BOS #. Accuracy depends on position
Oral	safe, convenient, and familiarity	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
Axillary	Non-invasive	Less than core body temperature, intermittent data

Discussion

The answer table from the college is a comprehensive response, and it is difficult to improve upon it without a swamp of useless detail.

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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