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

  • 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

  • Position-dependent
  • Risk of oesophageal trauma
  • Uncomfortable

Tympanic

  • Reflects hypothalamic and core temperature.

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

  • 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