When Temperature Monitoring Is Required
The local anesthetics (including amides) used to produce regional
blocks and the sedatives used during monitored anesthesia care do not trigger malignant
hyperthermia.[219]
Nonetheless, core hypothermia
is as common during epidural and spinal anesthesia as during general anesthesia and
can be nearly as severe.[73]
Therefore, core temperature
should be measured during regional anesthesia in patients likely to become hypothermic
(e.g., those undergoing body cavity surgery).
Core temperature monitoring is appropriate during the administration
of most general anesthetics both to facilitate detection of malignant hyperthermia
and to quantify hyperthermia and hypothermia. Malignant hyperthermia is best detected
by tachycardia and an increase in endtidal PCO2
out of proportion to minute ventilation.[220]
Although
an increasing core temperature is not the first sign of acute malignant hyperthermia,
it certainly helps
confirm the diagnosis. More common than malignant hyperthermia is intraoperative
hyperthermia of other etiologies, including excessive warming, infectious fever,
blood in the fourth cerebral ventricle, and mismatched blood transfusions.
By far the most common perioperative thermal disturbance is inadvertent
hypothermia. Core temperature usually decreases 0.5°C to 1.5°C in the first
30 minutes after induction of anesthesia. Hypothermia results from internal redistribution
of heat and a variety of other factors whose importance in individual patients is
hard to predict.[57]
[77]
Core temperature perturbations during the first 30 minutes of anesthesia are thus
difficult to interpret, and measurements are not usually required. Body temperature
should, however, be monitored in patients undergoing general anesthesia exceeding
30 minutes in duration and in all patients whose surgery lasts longer than 1 hour.
