Review Note
Last Update: 03/30/2025 10:26 PM
Current Deck: ACG Part 2::Plastic Surgery and Burns
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Commit #312108
SS_PB 1.1 Describe the physiological principles relevant to optimising blood flow to tissue flaps, including:
∙ The physiological mechanisms controlling and regulating body temperature and the effects of anaesthesia
∙ The physiological mechanisms controlling and regulating body temperature and the effects of anaesthesia
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Commit #312108
Control of Body Temperature
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Sensors:
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Cold receptors (bulb of Krause) and warm receptors (bulb of Ruffini) in the skin detect temperature changes.
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Central Integrator:
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Hypothalamus serves as the body’s thermostat, regulating temperature around a set point.
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Anterior Hypothalamus: Responds to increased temperature by promoting heat loss via SNS (sweating, vasodilatation).
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Posterior Hypothalamus: Responds to decreased temperature by promoting heat conservation (shivering, thyroid activity, non-shivering thermogenesis).
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Effectors:
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SNS: Controls vasoconstriction, vasodilatation, sweating.
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Skin: Heat exchange occurs through radiation, conduction, convection, and evaporation.
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Brown fat and thyroid regulate metabolic heat production.
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Behavioral responses (e.g., seeking warmth or avoiding cold).
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Radiation: Transfer of heat via infrared radiation between objects not in contact.
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Conduction: Heat exchange between substances in direct contact.
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Convection: Transfer of heat to surrounding molecules (air or water).
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Evaporation: Heat lost through the latent heat of vaporization.
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Interthreshold Range: Range of core body temperatures over which no autonomic thermoregulatory response occurs (normally 0.2°C; can widen to 4°C under anaesthesia).
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Thermoneutral Zone: Range of environmental temperatures where body temperature regulation is unaffected by changes in metabolic rate, and oxygen consumption remains constant.
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Anaesthesia broadens the interthreshold range, making thermoregulatory responses less sensitive to changes in core body temperature.
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Limited options for temperature conservation:
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Loss of behavioral responses (e.g., seeking warmth, shivering).
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Reduced metabolic heat production.
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Cooling effects from cold atmosphere, IV fluids, and anaesthetic gases.
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The patient becomes essentially poikilothermic (unable to regulate body temperature effectively).
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Risk of Hypothermia: Anaesthetized patients are at increased risk due to these changes.
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Pre-warming: Pre-emptive warming of the patient before anaesthesia induction.
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Active Warming:
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Bair hugger or forced-air warming systems.
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Insulation blankets.
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Warmed IV fluids.
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Humidified anaesthetic gases.
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Radiant heaters.
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Extensive or multiple surgical sites may limit access to the patient's body surface area, making temperature maintenance challenging.
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Under-body blankets can be useful to help maintain temperature