Virtually all pediatric patients become hypothermic in the perioperative period, unless measures are taken to maintain normothermia. Hypothermia leads to a variety of complications, including delayed emergence, prolonged neuromuscular blockade, platelet dysfunction, increased oxygen consumption upon emergence, and poor wound healing. Thus, the anesthesiologist must continuously monitor core temperature and actively prevent heat loss in the operating room (OR), as well as in the postanesthesia care unit (PACU). Keep in mind that there are actually a number of reasons for heat loss. Also, cooling begins with exposure of the patient upon removal of his clothing; accordingly, do not have the baby undressed until it is necessary.

The most important type of heat loss is via radiation, but convection, conduction, and evaporation also play a role. Most ORs are kept extremely cold, which allows for tremendous radiant heat loss to the OR environment. Next, the surgical site is prepped with cold solution, which partially evaporates from the skin, decreasing the body’s temperature further. Other evaporative losses occur from surgical incisions as well as from the airway. Volatile anesthetics cause vasodilation, which brings heat to the cutaneous surface where it can participate in heat exchange with the environment. During the first half hour of anesthesia, it is this redistribution of heat from the core to the periphery that causes the patient’s temperature to drop 0.5° to 1.5° C. General anesthesia also impairs normal function of the body’s thermoregulatory center, the hypothalamus. Under normal circumstances, the vessels of the body constrict to conserve heat, while metabolic heat production is increased. Peripheral vasodilation is combined with a 20% decease in heat production, thus altering the thermal steady state.

Heat loss is directly proportional to surface area. Because infants and neonates have a very large surface-area-to-volume ratio, they are particularly prone to becoming hypothermic. In addition, metabolic heat production is a function of mass. Therefore, not only do they lose heat faster, but they are less capable of producing heat. Infants and neonates do not shiver. Instead, they produce heat via nonshivering thermogenesis, which takes place primarily in brown fat. This mechanism of heat production, which continues until 2 years of age, is inhibited by anesthesia and sympathetic blockade.

For the many aforementioned reasons, anesthesiologists often battle intraoperative hypothermia on a regular basis. This has led to the development of various mechanisms that can be used to maintain normothermia during anesthesia. Some of the methods are simple and can be of tremendous benefit. Warming the operating room by 1° C will decrease the patient’s heat loss by 7%. This is an easy and effective means of preventing heat loss form the start of the procedure. Passive insulators, such as blankets or plastic bags wrapped around the exposed surfaces of the body, may reduce heat losses up to 30%. An infant’s head is a major source of heat loss, given its large surface area, and should be wrapped to decrease radiant heat losses. Warming intravenous fluids helps prevent hypothermia during longer procedures with greater fluid requirements. It has been shown that 1 L of room-temperature fluid given to an adult reduces core temperature between 0.25° and 1.0° C. A similar result is seen in children receiving a comparable volume of unwarmed fluid. Circulating water mattresses are used less often to reduce conductive heat losses. Their effectiveness is limited, given that they only reduce the already minimal heat loss from a patient’s back. Warming lights, infrared heaters, and warm preparatory and irrigation solutions may also be of benefit.