Human beings maintain a core body temperature of approximately 36.5–37.5°C through thermoregulation, which is controlled by the hypothalamus. However, under anesthesia, the mechanisms that normally regulate temperature are significantly weakened (1). The pharmacological actions of commonly used anesthetic agents, which alter vascular regulation, suppress thermoregulatory thresholds, and accelerate heat redistribution, can impact core body temperature and must be accounted for in anesthesia care.

Typically, anesthetic agents produce a decrease in core body temperature. A major mechanism contributing to early temperature decline is core-to-peripheral redistribution of heat, which occurs because anesthetic agents impair peripheral vasoconstriction. Volatile anesthetics such as sevoflurane, desflurane, and isoflurane are vasodilators that rapidly inhibit the body’s ability to restrict warm blood to the core (1). Even at low concentrations, these agents lower the threshold for vasodilation, enabling heat to flow outward into cooler tissues. This explains the characteristic drop in core temperature seen shortly after induction with inhaled agents. Intravenous agents such as propofol have similar effects, though they differ slightly from volatile agents in their influence on vasomotor tone and redistribution kinetics (2). Together, these drugs prevent the body from conserving heat as passive heat loss increases under procedural conditions.

Anesthesia also depresses the activation points for heat-preserving responses. Typically, a slight temperature decrease prompts vasoconstriction, followed by shivering if necessary. However, under the influence of volatile and intravenous anesthetics, these thresholds shift downward by several degrees (3). Thus, the core body temperature can fall well below the normal regulatory set point before corrective mechanisms engage. The combination of vasodilation and delayed thermoregulatory activation makes anesthetized patients uniquely vulnerable to progressive hypothermia unless external warming measures are applied.

Environmental conditions can exacerbate the effects of anesthetic agents. Operating rooms are typically cool, and surgical exposure increases heat loss through radiation, convection, and evaporation (3). Because anesthetic agents suppress shivering and behavioral adjustments, patients cannot compensate for these external stresses. Accurate monitoring is essential because peripheral sites may not accurately reflect core thermal status, which can lead to an underestimation of the severity of hypothermia.

Even moderate reductions in core temperature have important clinical consequences. Hypothermia can impair coagulation, increase the risk of surgical-site infection, alter drug metabolism, and prolong recovery time. During emergence, the body may attempt to restore normothermia through shivering, which is an energetically costly process that increases oxygen consumption and may strain the cardiovascular system. Proactive thermal management significantly reduces these complications. Forced-air warming, warmed intravenous fluids, and prewarming strategies counteract anesthetic-induced redistribution and peripheral heat loss (4). Therefore, maintaining core temperature is a critical component of safe anesthetic care.

Anesthetic agents disrupt thermoregulation by impairing vasoconstriction, lowering temperature-defense thresholds, and promoting the redistribution of heat from the core to the periphery, leading to decreased core body temperature if external warming strategies are insufficient. Volatile anesthetics such as sevoflurane, desflurane, and isoflurane and intravenous agents such as propofol commonly contribute to these physiological changes. Combined with environmental exposure, these agents place patients at high risk for unintended hypothermia. Effective perioperative warming and continuous core temperature monitoring are essential to counteracting these well-characterized effects and improving surgical outcomes.

References

1. Sessler DI. Temperature monitoring and perioperative thermoregulation. Anesthesiology. 2008;109(2):318-338. doi:10.1097/ALN.0b013e31817f6d76

2. Ikeda T, Sessler DI, Kikura M, Kazama T, Ikeda K, Sato S. Less core hypothermia when anesthesia is induced with inhaled sevoflurane than with intravenous propofol. Anesth Analg. 1999;88(4):921-924. doi:10.1097/00000539-199904000-00044

3. Lenhardt R. Body temperature regulation and anesthesia. Handb Clin Neurol. 2018;157:635-644. doi:10.1016/B978-0-444-64074-1.00037-9

4. Rauch S, Miller C, Bräuer A, Wallner B, Bock M, Paal P. Perioperative Hypothermia-A Narrative Review. Int J Environ Res Public Health. 2021;18(16):8749. Published 2021 Aug 19. doi:10.3390/ijerph18168749