INTRAOPERATIVE HEAT CONSERVATION - A BUNC H OF HOT AIR

Thermoregulation and its impairment by anaesthesia and surgery has rec ently been brought back into focus by researchers and clinicians. All Volatile and IV anaesthetics, opioids, as well as spinal and epidural anaesthesia increase the inter-threshold range of thermoregulation fro m 0.2 degrees C to 4 degrees C between vasodilation and vasoconstricti on. Thermoregulatory vasoconstriction and shivering occurs in anaesthe tized patients at lower core temperatures than in awake subjects. Foll owing induction of general or spinal/epidural anaesthesia,care tempera ture decreases significantly due to internal redistribution of body he at from the core thermal compartment to peripheral tissues. About 1 h after induction of general anaesthesia and initial redistribution hypo thermia, a real reduction in body heat occurs as heat loss exceeds met abolic heat production. Heat loss is further increased due to low oper ating room temperatures, evaporation from open body cavities,and cold IV fluids. Peripheral thermoregulatory vasoconstriction is triggered b y core temperatures between 33 degrees C and 35 degrees C,and is able to slow heat loss. However body heat content continues to decrease eve n though core temperatures remain nearly constant. During spinal or ep idural anaesthesia thermoregulation remains intact in the unblocked bo dy segments, leading to reduced real heat loss when compared to genera l anaesthesia. Inadvertent hypothermia markedly decreases drug metabol ism. Coagulation is impaired by cold-induced defects of platelet funct ion. Hypothermia reduces neutrophil phagocytosis and oxidative killing capacity, causing wound infections. Postoperative hypothermia represe nts an unnecessary stress for the circulatory system, elevating plasma catecholamines and leading to myocardial ischaemia and arrhythmias. T hese hypothermia-related morbidities therefore have consequences reach ing fare into the postoperative period. Prevention of inadvertent hypo thermia is always indicated. Forced-air warming is the most effective and safest method to prevent perioperative hypothermia.