Heat results from the human body’s natural metabolic processes, such as ATP breakdown, protein synthesis, and most other homeostasis reactions. Heat released during these reactions needs to be removed from the body in an efficient and timely fashion to maintain normothermia because most physiologic processes within a cell function within a narrow temperature range. Small derangements in temperature, high or low, can lead to organ system failure. Key mechanisms employed to dissipate excess heat are radiation, conduction, convection, and evaporation.
Hyperthermia and fever are different terms. Hyperthermia is an increase in temperature while fever is the body’s controlled increase of its thermoregulatory system (Table 103-1).
TABLE 103-1Temperature Ranges
The primary causes of nonmalignant hyperthermia are as listed.
Serotonin syndrome—This is caused by exposure to medications, including SSRI, MAOI, tryptophan, and amphetamines. These reactions range from mild to life threatening. The classic trait associated with serotonin syndrome includes hyperthermia, altered mental status, neuromuscular excitation (lead-pipe rigidity), and autonomic instability. Treatment involves supportive care, withdrawal of the offending agent and potential sedation, and muscle relaxation.
Neuroleptic malignant syndrome—A potentially life-threatening complication associated with use of antipsychotic medications. The clinical symptoms consist of hyperthermia, severe muscle rigidity, autonomic instability, and altered mental status.
Sympathomimetic toxicity—Leads to hyperthermia associated with the use of amphetamines, cocaine, and amphetamine derivatives. Other clinical signs include agitation, hypertensive crisis, coronary or cerebral vasospasm, dysrhythmias, acidosis, seizures, and hyperkalemia.
Anticholinergic syndrome—A condition associated with antihistamines, antipsychotics, TCAs, and anticholinergic plants. Hallmark symptoms include hyperthermia, tachycardia, blurry vision, dry skin, urinary retention, lethargy, and hallucinations. Treatment includes increasing acetylcholine via an anticholinesterase medication.
Blood Product and Infectious Reactions
There are a variety of transfusion reactions that can lead to hyperthermia as well as other sequela. These reactions include, but are not limited to, febrile nonhemolytic, ABO incompatibility, and transfusion-associated lung injury.
Infections can lead to a febrile reaction, including abscess, sepsis, respiratory, cellulitis, meningitis, or any other infection. Fever is the body’s response to infection, which needs to be diagnosed and treated appropriately with antibiotics and supportive therapies.
Exogenous Heating Sources
Forced air warming, fluid warming devices, cardiopulmonary bypass machines, closed anesthesia circuits, humidity moisture exchangers, and other warming devices warm patients intraoperatively. If the devices malfunction or are not monitored closely, unintentional hyperthermia may result.
The endocrine system often controls metabolic activity. Various pathologic hypermetabolic states may lead to hyperthermia if left untreated: thyroid storm, pheochromocytoma, and adrenal insufficiency are several examples.
Pulmonary—Numerous pulmonary processes lead to hyperthermia such as aspiration, atelectasis, pulmonary embolism, ...