Chapter 017. Fever and Hyperthermia (Part 2)

HyperthermiaAlthough most patients with elevated body temperature have fever, there are circumstances in which elevated temperature represents not fever but hyperthermia (Table 17-1). Hyperthermia is characterized by an uncontrolled increase in body temperature that exceeds the bodys ability to lose heat. The setting of the hypothalamic thermoregulatory center is unchanged. In contrast to fever in infections, hyperthermia does not involve pyrogenic molecules (see "Pyrogens," below). Exogenous heat exposure and endogenous heat production are two mechanisms by which hyperthermia can result in dangerously high internal temperatures. Excessive heat production can easily cause hyperthermia despite physiologic and behavioral control of body...
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Chapter 017. Fever and Hyperthermia (Part 2) Chapter 017. Fever and Hyperthermia (Part 2) Hyperthermia Although most patients with elevated body temperature have fever, thereare circumstances in which elevated temperature represents not fever buthyperthermia (Table 17-1). Hyperthermia is characterized by an uncontrolledincrease in body temperature that exceeds the bodys ability to lose heat. Thesetting of the hypothalamic thermoregulatory center is unchanged. In contrast tofever in infections, hyperthermia does not involve pyrogenic molecules (seePyrogens, below). Exogenous heat exposure and endogenous heat production aretwo mechanisms by which hyperthermia can result in dangerously high internaltemperatures. Excessive heat production can easily cause hyperthermia despitephysiologic and behavioral control of body temperature. For example, work orexercise in hot environments can produce heat faster than peripheral mechanismscan lose it. Table 17-1 Causes of Hyperthermia Syndromes Heat Stroke Exertional: Exercise in higher-than-normal heat and/or humidity Nonexertional: Anticholinergics, including antihistamines; antiparkinsoniandrugs; diuretics; phenothiazines Drug-Induced Hyperthermia Amphetamines, cocaine, phencyclidine (PCP),methylenedioxymethamphetamine (MDMA; ecstasy), lysergic aciddiethylamide (LSD), salicylates, lithium, anticholinergics, sympathomimetics Neuroleptic Malignant Syndrome Phenothiazines; butyrophenones, including haloperidol and bromperidol;fluoxetine; loxapine; tricyclic dibenzodiazepines; metoclopramide; domperidone;thiothixene; molindone; withdrawal of dopaminergic agents Serotonin Syndrome Selective serotonin reuptake inhibitors (SSRIs), monoamine oxidaseinhibitors (MAOIs), tricyclic antidepressants Malignant Hyperthermia Inhalational anesthetics, succinylcholine Endocrinopathy Thyrotoxicosis, pheochromocytoma Central Nervous System Damage Cerebral hemorrhage, status epilepticus, hypothalamic injury Source: After FJ Curley, RS Irwin, JM Rippe et al (eds): Intensive CareMedicine, 3d ed. Boston, Little, Brown, 1996.Heat stroke in association with awarm environment may be categorized as exertional or nonexertional. Exertionalheat stroke typically occurs in individuals exercising at elevated ambienttemperatures and/or humidities. In a dry environment and at maximal efficiency,sweating can dissipate ~600 kcal/h, requiring the production of >1 L of sweat.Even in healthy individuals, dehydration or the use of common medications (e.g.,over-the-counter antihistamines with anticholinergic side effects) may precipitateexertional heat stroke. Nonexertionalheat stroke typically occurs in either veryyoung or elderly individuals, particularly during heat waves. According to theCenters for Disease Control and Prevention, there were 7000 deaths attributed toheat injury in the United States from 1979 to 1997. The elderly, the bedridden,persons taking anticholinergic or antiparkinsonian drugs or diuretics, andindividuals confined to poorly ventilated and non-air-conditioned environmentsare most susceptible.Drug-induced hyperthermia has become increasinglycommon as a result of the increased use of prescription psychotropic drugs andillicit drugs. Drug-induced hyperthermia may be caused by monoamine oxidaseinhibitors (MAOIs), tricyclic antidepressants, and amphetamines and by the illicituse of phencyclidine (PCP), lysergic acid diethylamide (LSD),methylenedioxymethamphetamine (MDMA, ecstasy), or cocaine.Malignanthyperthermia occurs in individuals with an inherited abnormality of skeletal-muscle sarcoplasmic reticulum that causes a rapid increase in intracellular calciumlevels in response to halothane and other inhalational anesthetics or tosuccinylcholine. Elevated temperature, increased muscle metabolism, musclerigidity, rhabdomyolysis, acidosis, and cardiovascular instability develop withinminutes. This rare condition is often fatal. The neuroleptic malignant syndromeoccurs in the setting of neuroleptic agent use (antipsychotic phenothiazines,haloperidol, prochlorperazine, metoclopramide) or the withdrawal ofdopaminergic drugs and is characterized by lead-pipe muscle rigidity,extrapyramidal side effects, autonomic dysregulation, and hyperthermia. Thisdisorder appears to be caused by the inhibition of central dopamine receptors inthe hypothalamus, which results in increased heat generation and decreased heatdissipation. The serotonin syndrome, seen with selective serotonin uptakeinhibitors (SSRIs), MAOIs, and other serotonergic medications, has manyoverlapping f ...