44

Monisha Bahri

7 Temperature Monitoring

Temperature measurement is an important part of normal

newborn care. Accurate measurement is important to

detect deviations from normal and also for optimal incubator and radiant warmer function.

The purpose of monitoring temperature is to maintain

the infant in a thermoneutral environment zone. This is

defined as the narrow range of environmental temperature in

which the infant maintains a normal body temperature without increasing metabolic rate and hence oxygen consumption.

Temperature monitoring may be done intermittently or

continuously. The site of measurement may be core (rectum,

esophagus, or tympanic) or surface (skin, axilla). Although

rectal temperature measurement remains the standard, the

axillary route is preferred, especially for preterm neonates.

The various methods are discussed further in this chapter.

Intermittent Temperature Monitoring

A. Equipment

1. Mercury-in-glass thermometer

a. Benchmark standard

b. Determination time >3 minutes.

c. Risk of breakage/mercury poisoning from vaporized

mercury (1).

d. The American Academy of Pediatrics (AAP) recommends that mercury thermometers be removed from

medical offices, medical facilities, and homes (1).

e. No longer used in neonatal units

2. Electronic digital thermometers (Fig. 7.1)

a. Most widely used

b. Thermometer is a small hand-held device.

c. Temperature sensor may be a thermistor or thermocouple.

d. Temperature is sensed by the probe; the signal is

then processed electronically and displayed digitally. There is an audible signal at the end of the

determination time window.

e. Determination time is <45 seconds.

f. Resolution is 0.1°C.

g. Probe-type electronic thermometers are designed to

be used with disposable probe covers.

3. Infrared electronic thermometry

a. Sensitive infrared sensor detects infrared energy

radiation from the site of measurement (e.g., tympanic membrane for aural thermometers or skin

sites over temporal artery, forehead, and axilla).

b. The sensor converts the infrared signal to an electrical signal.

c. Electrical signal is then processed and displayed

digitally as temperature.

d. Determination time is <2 seconds.

e. Designed to be used with disposable sensor head covers.

f. Cost-effective (2)

B. Limitations

1. Temperature measurements can vary from axillary sites

depending on the environment (e.g., radiant warmer,

open crib, or incubator) (3).

2. Axillary temperatures are usually significantly lower

that rectal temperatures in newborns (mean ± SD,

0.27 ± 0.20°C, p < 0.05) (4)

3. Although speed and ease of operation with infrared

thermometry may offer advantages over traditional clinical methods of temperature measurement, studies

have failed to show an adequate correlation between

infrared ear thermometer readings and rectal or axillary

measurements in newborns (5,6). Infrared thermometry is not the preferred method in situations where precision in body temperature measurement is needed.

C. Precautions

1. Probe-type electronic thermometers

a. Always use disposable probe cover.

b. Do not force probe, as perforation can occur (e.g.,

in rectal measurement).

2. Infrared thermometers

a. Always use disposable sensor head covers.

b. Do not force sensor head into the ear canal.

c. Do not use in infants with middle ear disease.

d. Do not use in very low-birthweight infants because

of inappropriate speculum size. Sensor head may

Chapter 7 ■ Temperature Monitoring 45

not be small enough for low-birthweight infants

weighing <1,000 g.

e. Erroneous readings may result from

(1) Not having the probe lined up with the tympanic membrane

(2) The presence of heavy cerumen

(3) The presence of serous otitis media (7)

D. Technique

1. Probe-type electronic thermometers

a. Apply disposable probe cover to the probe.

b. For core temperature, insert probe into the rectum

(2 to 3 cm).

c. For noninvasive approximation of core temperature,

place the probe in the axilla (Fig. 7.2) (8–10).

d. Hold the probe in place and wait for an audible

beep before removing the probe.

e. Read temperature and return the probe to its compartment to deactivate the unit.

2. Infrared thermometers

a. Apply disposable cover to the sensor head.

b. Gently insert tapered end into the ear canal.

c. While holding the unit steady, depress the trigger.

d. Remove from the ear canal and read temperature.

e. Remove used disposable cover.

E. Complications

1. Inaccurate reading (11–14)

2. Tissue trauma

a. Rectal or colonic perforation (11,15,16)

b. Pneumoperitoneum (17)

c. Peritonitis

3. Risk of trauma to the tympanic membrane

4. Thermometer housing unit can transmit infection; disinfect after each use.

Continuous Temperature Monitoring

A. Purpose

1. Provides reliable continuous monitoring of neonatal

body temperature

2. Provides trend of temperature over time

3. Provides automated environmental control (Fig. 7.3)

4. Probes used for continuous core temperature monitoring may be used for servocontrol of cooling blankets in

whole-body cooling protocols (Chapter 45).

B. Background

1. Sites used may be surface (e.g., skin over the abdomen)

or core (e.g., rectum, esophagus).

FIG. 7.1. Electronic thermometers: Probe thermometer. (Courtesy

of Welch Allyn, New York, USA.)

Fig. 7.2. Axillary temperature being taken with an

electronic probe thermometer. The probe is held perpendicular to the patient, and the arm is held securely

against the side of the chest.