Unplanned perioperative hypothermia

AORN Journal, Feb, 2006 by V. Doreen Wagner

Maintenance of core body temperature in surgical patients receiving general or regional anesthesia presents a constant challenge for perioperative nurses because all patients are at risk for lowered body temperatures during surgery. In the OR, hypothermia may be planned or unplanned. Planned hypothermia is used during certain surgeries (eg, coronary artery bypass) to lessen metabolic demands and protect vital organs during low blood flow periods. (1,2)

Unplanned hypothermia can cause serious patient problems. Even mild hypothermia (ie, temperature < 36[degrees] C [< 96.8[degrees] F]) has been consistently linked with perioperative patient complications, including

* shivering,

* wound infections,

* cardiovascular ischemia,

* coagulopathy,

* altered drug metabolism, and

* prolonged postoperative recovery. (3-9)

This article discusses causes and prevention of hypothermia, current organizational and regulatory policies regarding patient temperature regulation, and the need for additional health care policy development to stop the harm that occurs from allowance of unplanned perioperative hypothermia. Perioperative nurses can prevent the chilling outcomes of unplanned hypothermia by enacting, supporting, and formalizing policy in the perioperative arena.

CAUSES OF HYPOTHERMIA

When a surgical patient undergoes general anesthesia or major regional anesthesia (eg, epidural anesthesia) for periods longer than one hour, hypothermia is expected because anesthesia disrupts the behavioral and physiological mechanisms of thermoregulation. (10,11)

During that first hour of anesthesia, the patient's core temperature usually drops 0.5[degrees]C to 1.5[degrees] C (0.9[degrees]F to 2.7[degrees]F). This drop in core temperature can be explained by redistribution of heat from the body's core to the extremities. Vasodilation from anesthetic agents potentiates this redistribution of heat. (10,12)

Extrinsic factors, other than anesthetic agents, that place surgical patients at risk for developing hypothermia include the cold OR environment, length and type of the surgical procedure, major fluid or blood loss, infusion of cold fluids or blood products, large volumes of irrigation into body cavities, and exposure of a large body cavity. (9,11) Factors that place patients at intrinsic risk for developing hypothermia include

* age--infants and children cool more quickly because of their high ratio of surface area to weight (13) and older adult patients also cool quickly due to decreased thermo-regulatory efficiency; (14,15)

* body size--thin or small-stature patients with a lack of tissue mass are more likely to become hypothermic; (12) and

* physical status and comorbidities--endocrine diseases, in particular, cause patients to be more prone to hypothermia. (3,10,12)

PREVENTION OF HYPOTHERMIA

Surgery commonly causes alterations in temperature, so patients' body temperatures should be monitored routinely during the perioperative period. The most significant change in temperature occurs during the first 60 minutes of the surgical procedure. (11,12,16) Consequently, the patient's temperature should be monitored when the length of the procedure exceeds 30 minutes. The decision to monitor temperature during local anesthesia, conscious sedation, or monitored anesthesia care depends on the length of the procedure, the anticipated amount of blood loss, and the patient's risk status. If the patient's temperature is changing rapidly, more frequent assessments should be performed. (1,11,17)

Maintaining normothermia. Maintaining a normal patient temperature, especially during the intraoperative period, is important for both patient comfort and the prevention of complications that result from hypothermia. Research-based evidence identifies that the normalization of body temperature during the perioperative period significantly improves patient outcomes and patient satisfaction, and dramatically reduces the cost of treating complications related to unplanned perioperative hypothermia. (6-8,17-20)

Warming measures to prevent hypothermia should begin in the preoperative period, using basic nursing approaches to decrease patient anxiety and increase comfort, combined with active thermal protection measures that continue through the perioperative period. Management of normothermia should be performed consistently throughout perioperative care. This management includes both temperature monitoring and thermal protection measures. (21)

Warming devices that are commonly available include warmed cotton blankets, thermal drapes, fluid warmers, water mattresses, and forced-air warming systems. A meta-analysis of studies regarding different warming methods, however, showed forced-air warming systems to be the most effective method to prevent and treat perioperative hypothermia. The clinical literature clearly demonstrates the superiority of forced-air warming compared to other warming devices. The practice guideline issued by the American Society of PeriAnesthesia Nurses (ASPAN) recognizes that forced-air warming represents the first line of intervention to normalize temperature. (1)