Temperature Regulation
Temperature regulation maintains core temperature 36.5-37.5°C through balance of heat production, conservation, and loss, regulated by the hypothalamus. Heat production: Basal metabolic rate (BMR, 80 W at rest),...
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Urgent signals
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- Malignant hyperthermia (rapid temperature rise >38.8°C)
- Severe hypothermia <32°C with arrhythmias
- Heat stroke with core temperature >40°C
- Hypothermia-induced coagulopathy
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- ANZCA Primary Written
- ANZCA Primary Viva
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Temperature regulation is a fundamental homeostatic mechanism that maintains core body temperature within a narrow range... CICM Fellowship Written, CICM Fellow
Temperature regulation maintains core temperature 36.5-37.5°C through balance of heat production, conservation, and loss, regulated by the hypothalamus. Heat production: Basal metabolic rate (BMR, 80 W at rest), muscle...
Quick Answer
Temperature regulation maintains core temperature 36.5-37.5°C through balance of heat production, conservation, and loss, regulated by the hypothalamus. Heat production: Basal metabolic rate (BMR, 80 W at rest), muscle activity (shivering increases heat production 2-5×), thermogenic hormones (thyroxine, catecholamines), brown fat metabolism (neonates). Heat loss: Radiation (60%, infrared emission), convection (15%, air currents), conduction (3%, direct contact), evaporation (22%, sweating, respiration); regulated by skin blood flow (vasodilation/vasoconstriction) and sweating. Hypothalamic regulation: Preoptic anterior hypothalamus (POAH) contains temperature-sensitive neurons; set point maintained; deviation triggers responses: cold—shivering, piloerection, peripheral vasoconstriction; heat—vasodilation, sweating, behavioral responses. Anaesthetic effects: General anaesthetics impair hypothalamic regulation and abolish behavioral responses; vasodilation promotes heat loss; patients cannot shiver under GA; hypothermia (core temperature <36°C) occurs in 50-90% of surgical patients without active warming; phases—redistribution (first hour, core heat moves to periphery due to vasodilation), linear decline (continued heat loss exceeding production), plateau (thermal equilibrium if heat loss equals production). Complications of hypothermia: Increased surgical site infection (impaired immune function), coagulopathy (platelet dysfunction, enzyme inhibition—each 1°C drop reduces coagulation factor activity 10%), increased blood loss, prolonged drug action (reduced hepatic metabolism), shivering in PACU (increases oxygen consumption 200-500%, myocardial stress), thermal discomfort, delayed wound healing. Prevention: Forced air warming (most effective—Bair Hugger, reduces heat loss, can add heat), warmed IV fluids (minimal effect unless large volumes), increased ambient temperature (OR to 24-26°C initially then lower to 21-22°C), circulating water mattresses, radiant warmers (neonates). Malignant hyperthermia: Pharmacogenetic disorder triggered by volatile agents and suxamethonium; uncontrolled hypermetabolism in skeletal muscle; temperature rises late (not early sign); early signs—tachycardia, tachypnea, increased CO₂, rigidity; treatment—dantrolene 2.5 mg/kg IV (inhibits Ca²⁺ release from sarcoplasmic reticulum), cooling, supportive care. Hypothermia treatment: Gradual rewarming; active external (forced air, warm blankets), active internal (warmed IV fluids, body cavity lavage, cardiopulmonary bypass if severe); avoid rapid rewarming (risk of arrhythmias, afterdrop—core temperature continues to fall after rewarming starts due to cold blood returning from periphery). Therapeutic hypothermia: 32-34°C for 24 hours post-cardiac arrest (neuroprotection); targeted temperature management. Indigenous populations: Higher rates of obesity and metabolic syndrome; careful temperature monitoring and active warming essential. [1-10]