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

  • 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.

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