Validity of devices that assess body temperature during outdoor exercise in the heat

Abstract

Context: Rectal temperature is recommended by the National Athletic Trainers' Association as the criterion standard for recognizing exertional heat stroke, but other body sites commonly are used to measure temperature. Few authors have assessed the validity of the thermometers that measure body temperature at these sites in athletic settings.

Objective: To assess the validity of commonly used temperature devices at various body sites during outdoor exercise in the heat.

Design: Observational field study.

Setting: Outdoor athletic facilities.

Patients or other participants: Fifteen men and 10 women (age = 26.5 +/- 5.3 years, height = 174.3 +/- 11.1 cm, mass = 72.73 +/- 15.95 kg, body fat = 16.2 +/- 5.5%).

Intervention(s): We simultaneously tested inexpensive and expensive devices orally and in the axillary region, along with measures of aural, gastrointestinal, forehead, temporal, and rectal temperatures. Temporal temperature was measured according to the instruction manual and a modified method observed in medical tents at local road races. We also measured forehead temperatures directly on the athletic field (other measures occurred in a covered pavilion) where solar radiation was greater. Rectal temperature was the criterion standard used to assess the validity of all other devices. Subjects' temperatures were measured before exercise, every 60 minutes during 180 minutes of exercise, and every 20 minutes for 60 minutes of postexercise recovery. Temperature devices were considered invalid if the mean bias (average difference between rectal temperature and device temperature) was greater than +/-0.27 degrees C (+/-0.5 degrees F).

Main outcome measure(s): Temperature from each device at each site and time point.

Results: Mean bias for the following temperatures was greater than the allowed limit of +/-0.27 degrees C (+/-0.5 degrees F): temperature obtained via expensive oral device (-1.20 degrees C [-2.17 degrees F]), inexpensive oral device (-1.67 degrees C [-3.00 degrees F]), expensive axillary device (-2.58 degrees C [-4.65 degrees F]), inexpensive axillary device (-2.07 degrees C [-3.73 degrees F]), aural method (-1.00 degrees C [-1.80 degrees F]), temporal method according to instruction manual (-1.46 degrees C [-2.64 degrees F]), modified temporal method (-1.36 degrees C [-2.44 degrees F]), and forehead temperature on the athletic field (0.60 degrees C [1.08 degrees F]). Mean bias for gastrointestinal temperature (-0.19 degrees C [-0.34 degrees F]) and forehead temperature in the pavillion (-0.14 degrees C [-0.25 degrees F]) was less than the allowed limit of +/-0.27 degrees C (+/-0.5 degrees F). Forehead temperature depended on the setting in which it was measured and showed greater variation than other temperatures.

Conclusions: Compared with rectal temperature (the criterion standard), gastrointestinal temperature was the only measurement that accurately assessed core body temperature. Oral, axillary, aural, temporal, and field forehead temperatures were significantly different from rectal temperature and, therefore, are considered invalid for assessing hyperthermia in individuals exercising outdoors in the heat.

Keywords: core body temperature; hyperthermia; tympanic membrane temperature.

Figure 1. Mean ± SD of each temperature device over time compared with RCT. RCT = rectal temperature, ORL _IE = oral temperature with inexpensive thermometer, ORL _E = oral temperature with expensive thermometer, AXL _IE = axillary temperature with inexpensive thermometer, AXL _E = axillary temperature with expensive thermometer, INT = intestinal temperature, AUR = aural temperature, TEM _INST = temporal temperature measured with the method described by the instructional manual, TEM _MOD = temporal temperature measured in a modified method, FST = forehead sticker temperature, and FST _FLD = forehead temperature measured on the field. (See text for further description.) *Indicates significant difference from RCT at the same time point ( P < .05)

Figure 2. Bland-Altman plots indicating the mean bias (bold dashed line) and limits of agreement (dashed lines) for each temperature device compared with RCT. RCT = rectal temperature, ORL _IE = oral temperature with inexpensive thermometer, ORL _E = oral temperature with expensive thermometer, AXL _IE = axillary temperature with inexpensive thermometer, AXL _E = axillary temperature with expensive thermometer, INT = intestinal temperature, AUR = aural temperature, TEM _INST = temporal temperature measured with the method described by the instructional manual, TEM _MOD = temporal temperature measured in a modified method, FST = forehead sticker temperature, and FST _FLD = forehead temperature measured on the field. (See text for further description)

Figure 2. Bland-Altman plots indicating the mean bias (bold dashed line) and limits of agreement (dashed lines) for each temperature device compared with RCT. RCT = rectal temperature, ORL _IE = oral temperature with inexpensive thermometer, ORL _E = oral temperature with expensive thermometer, AXL _IE = axillary temperature with inexpensive thermometer, AXL _E = axillary temperature with expensive thermometer, INT = intestinal temperature, AUR = aural temperature, TEM _INST = temporal temperature measured with the method described by the instructional manual, TEM _MOD = temporal temperature measured in a modified method, FST = forehead sticker temperature, and FST _FLD = forehead temperature measured on the field. (See text for further description)