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Pediatric Hyperthermia


Case Synopsis

A healthy 12-year-old boy is undergoing a tympanomastoidectomy under general anesthesia with sevoflurane in oxygen and air, and supplemented with fentanyl. He has also received dexamethasone, ondansetron, and cefazolin. Approximately 2 hours into the case, he is noted to have an esophageal temperature of 38.1°C. His heart rate is 120 beats per minute, and his blood pressure is 122/78 mm Hg. Except for a great aunt who died during surgery 25 years ago for unknown reasons, there is no other history of familial problems with anesthesia.

Problem Analysis

Definition

Although anesthetic and opioid impairment of thermoregulatory control often predisposes anesthetized patients to temperature instability, hyperthermia can cause serious complications, and anesthesiologists must be able to identify the underlying causes.

Strictly speaking, hyperthermia can be defined as any elevation in core temperature, but the usually accepted definition of hyperthermia is a core body temperature greater than 38°C. Temperature is regulated by a hypothalamic set point to which current core body temperature is continually compared. Hyperthermia occurs when the set point in the hypothalamus is raised, when thermoregulatory responses such as sweating or vasodilation are impaired, or as a result of excessive heat exposure. Regardless of the cause, hyperthermia is metabolically stressful and can affect end-organ function when severe ( Box 197.1 ).

BOX 197.1
Adverse Effects of Severe Hyperthermia
Data from Walter EJ, Hanna-Jumma S, Carraretto M, et al: The pathophysiological basis and consequences of fever. Crit Care 20(1):200, 2016.

  • Cardiovascular

    • Increase in cardiac output

    • Conduction defects (QT and ST changes, T-wave abnormalities)

  • Respiratory

    • Pulmonary edema

  • Renal

    • Decrease in GFR

    • Renal hypoperfusion contributing to acute kidney injury

  • Hepatic

    • Hepatocellular damage resulting in elevations of AST and ALT

    • Coagulopathy

  • Hematologic

    • Thrombocytopenia

    • DIC

  • Neurologic

    • Cognitive dysfunction

    • Disruption in the blood-brain barrier

  • Gastrointestinal

    • Ischemia

    • Hemorrhage

ALT, Alanine transaminase; AST, aspartate transaminase; DIC, disseminated intravascular coagulation; GFR, glomerular filtration rate.

The American Society of Anesthesiologists’ standards for basic anesthetic monitoring state that “every patient receiving anesthesia shall have temperature monitored when clinically significant changes in body temperature are intended, anticipated or suspected.” The Malignant Hyperthermia Association of the United States (MHAUS) recommends core temperature monitoring for all patients who receive general anesthesia for more than 30 minutes, because lack of temperature monitoring in this setting has been associated with increased mortality related to development of acute MH.

Recognition

Core temperature can be measured in the pulmonary artery, distal esophagus, tympanic membrane, or nasopharynx and is the best indicator of thermal status. However, core temperature measurements may not be feasible for all surgical procedures; thus estimates of core temperature are obtained using oral, axillary, rectal, bladder, and skin-surface temperature probes that have variable accuracy ( Table 197.1 ). In particular, skin-surface and rectal temperatures may not track core temperature in a timely manner and should be used with caution.

TABLE 197.1
Temperature Monitoring Locations and Considerations
Core Temperature Sites
Location Considerations
Pulmonary artery Invasive and only used during cardiac or similarly complicated procedures; potential pulmonary and cardiac complications with insertion
Distal esophagus Temperature probe incorporated into esophageal stethoscope must be positioned at point of maximal heart sounds or more distally for accurate temperature readings
Tympanic membrane Difficult to place accurately; fear of perforation
Nasopharynx Difficult to place accurately

Sites That Approximate Core Temperature
Location Considerations
Axillary Most accurate when probe is placed over the axillary artery and when the arm is kept maximally adducted
Bladder Invasive; must have urine flow to be accurate
Skin Does not reliably track core temperature; forehead skin temperature typically 2°C cooler than core
Rectal Difficult to place accurately; depends on rectal contents; often lags behind core temperature

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