18
Body Sites for Temperature Assessment
Under certain conditions, rectal temperature is even contraindicated; for example, severe arterial insuffi-
ciency in one or both legs might be associated with falsely low readings,
or in conditions affecting periph-
eral blood flow such as cardiogenic shock. More common contraindications include neutropenia, severe
hemorrhoids, and recent anorectal surgery. A less common but serious complication of rectal temperature
measurement is perforation of the rectum, which has even occurred in the absence of predisposing rectal
pathology.
Rectal temperature measurement is not well tolerated by either the patient or the caregivers, and is un-
comfortable and embarrassing. Rectal temperature is subject to inaccuracies of placement, environment,
and time of insertion. Although it is well established that a rectal temperature requires two to five minutes
or more to reach optimum measurement with a glass mercury thermometer, in practice many are with-
drawn in just one minute, a technique responsible for misleadingly low readings.
In fact, it is difficult to attribute any thermal significance at all to the rectal area. It is not known to contain
any thermoreceptive elements and its geographical location distances it from both the CNS and the cross-
roads of circulation at the heart, which are the vital informational elements.
TTTTTym
ym
ym
ym
ympanic Membrane and Ear T
panic Membrane and Ear T
panic Membrane and Ear T
panic Membrane and Ear T
panic Membrane and Ear Tem
em
em
em
emperature
perature
perature
perature
perature
A temperature site of more recent onset is the ear. It is a compelling site, accessible, free from bodily
fluids, and not easily influenced by patient activity. This temperature is measured using infrared technol-
ogy, and there are three types of infrared thermometers: tympanic, ear, and arterial heat balance. It has,
however, become common practice to refer to any thermometer making the measurement at the ear as a
tympanic thermometer. Although the terms tympanic and ear may be used interchangeably, they actually
describe quite different measurements.
TTTTTrue T
rue T
rue T
rue T
rue Tym
ym
ym
ym
ympanic Membrane T
panic Membrane T
panic Membrane T
panic Membrane T
panic Membrane Tem
em
em
em
emperature
perature
perature
perature
perature
The tympanic membrane is deep inside the skull, and is not subject to the artifactual errors that can affect
oral, rectal, axillary and ear temperatures. True tympanic thermometers provide an uncorrected, direct
reading of the temperature of the tympanic membrane, and are preferred for continual measurement
during certain surgical procedures, and for use in extreme conditions such as military use, research, and
sporting events.
There are two types of instrument used to make the measurement. One is a long thin thermocouple probe,
usually fitted with cotton at the end, that must come in contact with the tympanic membrane.
There is
much historical data on the efficacy of tympanic thermometry using contact thermocouples, stemming
originally from work done over thirty years ago. However, this method never gained wide acceptance due to
the risk of injury to the delicate membrane. The other type of instrument is the Exergen Ototemp 3000SD,
which scans the tympanic membrane without contact.
Ear T
Ear T
Ear T
Ear T
Ear Tem
em
em
em
emperature
perature
perature
perature
perature
Ear thermometry is a method of measuring the temperature of the external portion of the ear canal. For
routine clinical use, ear thermometry has been preferred as a simpler, faster, and more convenient alterna-
tive to true tympanic thermometry. The absolute temperature of the outer ear, however, is lower, and more
variable than tympanic membrane temperature. It is subject to a cooling effect resulting from the body
heat being radiated to the environment, and a heat balance method is required in order to produce the
requisite accuracy. When combined with an arterial heat balance method, ear thermometry provides a
highly accurate indication of body temperature, but those ear thermometers without it
have high rates of
missed fevers.
