title: Thermoregulatory defense mechanisms.
abstract: Core body temperature is normally tightly regulated by an effective thermoregulatory system. Thermoregulatory control is sometimes impaired by serious illness, but more typically remains intact. The primary autonomic defenses against heat are sweating and active precapillary vasodilation; the primary autonomic defenses against cold are arteriovenous shunt vasoconstriction and shivering. The core temperature triggering each response defines its activation threshold. Temperatures between the sweating and vasoconstriction thresholds define the inter-threshold range. The shivering threshold is usually a full 1 degrees C below the vasoconstriction threshold and is therefore a "last resort" response. Both vasoconstriction and shivering are associated with autonomic and hemodynamic activation; and each response is effective, thus impeding induction of therapeutic hypothermia. It is thus helpful to accompany core cooling with drugs that pharmacologically induce a degree of thermal tolerance. No perfect drug or drug combination has been identified. Anesthetics, for example, induce considerable tolerance, but are rarely suitable. Meperidine-especially in combination with buspirone-is especially effective while provoking only modest toxicity. The combination of buspirone and dexmedetomidine is comparably effective while avoiding the respiratory depression association with opioid administration.
authors.affiliation: Department of Outcomes Research, The Cleveland Clinic, Cleveland, OH, USA. ds@or.org
authors.forename: Daniel I
authors.initials: DI
authors.lastname: Sessler
mesh_terms: D000367:Age Factors; D000700:Analgesics / Q000627:therapeutic use; D018681:Anesthetics, General / Q000627:therapeutic use; D001341:Autonomic Nervous System / Q000187:drug effects / Q000502:physiology; D001833:Body Temperature Regulation / Q000187:drug effects / Q000502:physiology*; D002545:Brain Ischemia / Q000517:prevention & control; D002940:Circadian Rhythm / Q000502:physiology; D003422:Critical Care / Q000379:methods*; D004359:Drug Therapy, Combination; D019317:Evidence-Based Medicine; D005334:Fever / Q000503:physiopathology; D006801:Humans; D007036:Hypothermia, Induced / Q000009:adverse effects / Q000379:methods; D017202:Myocardial Ischemia / Q000517:prevention & control; D012684:Sensory Thresholds / Q000502:physiology; D012768:Shivering / Q000187:drug effects / Q000502:physiology*; D013816:Thermodynamics; D050051:Transient Receptor Potential Channels / Q000502:physiology; D016896:Treatment Outcome; D014661:Vasoconstriction / Q000187:drug effects / Q000502:physiology
chemical_list: D000700:Analgesics; D018681:Anesthetics, General; D050051:Transient Receptor Potential Channels