TEMPERATURE MONITORING

Core temperature measurements (e.g., tympanic membrane, pulmonary artery, distal portion of the esophagus, and nasopharynx) are used to monitor intraoperative hypothermia, prevent overheating, and facilitate detection of malignant hyperthermia. Muscle or skin surface temperatures may be used to evaluate vasomotion^[211] and ensure the validity of peripheral neuromuscular monitoring.^[212] Both core and skin surface temperature measurements are required to determine the thermoregulatory effects of different anesthetic drugs. Temperatures are not uniform within the body; consequently, temperatures measured at each site have different physiologic and practical significance.

Thermometers

Traditionally, the medical community has used mercury-in-glass thermometers. These slow and cumbersome thermometers have largely been replaced by electronic systems. The most common electronic thermometers are thermistors and thermocouples. Both devices are sufficiently accurate for clinical use and inexpensive enough to be disposable. Also sufficiently accurate for clinical use are "deep tissue" thermometers based on actively reducing cutaneous heat flux to zero^{[213] [214]} ; unfortunately, these monitors are not currently available in Europe or the United States. True infrared tympanic membrane thermometers are another alternative.^{[215] [216]} However, the more common infrared monitors that extrapolate tympanic membrane temperature from outer ear temperature are often unreliable,^[217] as are infrared systems that scan forehead skin.^[218]