How to prevent perioperative hypothermia in the dog and cat: causes and consequences
Abstract
Perioperative hypothermia is a common problem during anaesthesia in dogs and cats, and can have detrimental effects on the patient's physiology, such as impairment of kidney function. Veterinary nurses are usually heavily involved in veterinary anaesthesia, participating in pre-anaesthetic assessments, premedication, induction and monitoring of anaesthesia and observations during the recovery of the patient. Perioperative hypothermia is a problem that many veterinary nurses know must be prevented by using patient warming methods, but they may be unaware of the full pathophysiology of this condition and why certain preventative methods may or may not be successful. This article examines the causes of perioperative hypothermia, the consequences to the patients and the methods of prevention.
Heat production in the body occurs secondary to metabolism. The brain and major organs in the trunk generate the majority of metabolic heat due to the high number of chemical and physical processes taking place in these parts (Sessler, 2000). Normally, excess heat is dissipated into the environment through the respiratory tract and across the skin to maintain thermal homeostasis. The body is split into two thermal compartments: the core compartment consisting of the trunk and head; and the peripheral tissue compartment comprising the extremities (Armstrong et al, 2005). Core temperature remains consistent while peripheral temperature tends to vary (Armstrong et al, 2005). Heat moves slowly from the core to the periphery by conduction and convection. Conductive heat distribution occurs via adjacent tissues and depends on the characteristics of the tissue, for example fat insulates better than muscle thus slowing heat transfer. Convective heat distribution takes place via blood flow from the core to periphery and is influenced by peripheral blood flow, counter current heat exchange between arteries and veins, and the core-to-peripheral temperature gradient (Sessler, 2000).
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