Recommended practices for the prevention of unplanned perioperative hypothermia

AORN Journal, May, 2007

The following recommended practices for protecting patients from unplanned perioperative hypothermia were developed by the AORN Recommended Practices Committee and have been approved by the AORN Board of Directors. They were presented as proposed recommended practices for comments by members and others. They are effective May 1, 2007.

These recommended practices are intended as achievable recommendations representing what is believed to be an optimal level of practice. Policies and procedures will reflect variations in practice settings and/or clinical situations that determine the degree to which the recommended practices can be implemented.

AORN recognizes the various settings in which perioperative registered nurses practice. These recommended practices are intended as guidelines adaptable to various practice settings. Practice settings include traditional operating rooms, ambulatory surgery centers, physicians' offices, cardiac catheterization suites, endoscopy suites, radiology departments, and all other areas where operative and other invasive procedures may be performed.

PURPOSE. These recommended practices are intended to guide perioperative registered nurses in optimizing patient care practices to maintain normothermia and prevent unplanned hypothermia. Hypothermia, defined as a core body temperature less than 36[degrees]C (96.8[degrees]F), presents a constant challenge for perioperative registered nurses because many surgical patients are at risk for unplanned hypothermia during surgery. There are three phases of unplanned hypothermia: the redistribution phase, the linear decrease phase, and the thermal plateau phase. These recommended practices focus on the prevention of the redistribution phase of unplanned hypothermia. Planned or therapeutic hypothermia is outside the scope of this document.

In the redistribution phase of unplanned hypothermia, a rapid shift of body heat from the body's core to its periphery occurs, resulting in a core temperature drop of approximately 1.6[degrees]C (2.7[degrees]F) during the first hour after induction of anesthesia. (1,2) The initial temperature drop of the redistribution phase is followed by a slow, linear decrease phase during the second and subsequent hours of anesthesia, in which heat loss exceeds the body's ability to metabolically produce heat. In this second phase, warming the patient can effectively limit further heat loss. After approximately three to five hours of anesthesia, the patient's core temperature often plateaus and is characterized by a core body temperature that remains constant, even during prolonged surgery. (3,4)

Unplanned hypothermia is among the most common complications of surgery. It results from anesthesia-induced thermoregulation impairment and the heat loss inherent to surgery and the surgical environment. (5) The risk of hypothermia is greater in some patients (eg, neonates, (6,7) trauma patients, (8) patients with extensive burns (9)). All patients, however, are at risk of hypothermia as the duration of anesthesia time increases. (1,2,10,11)

Randomized clinical trials have demonstrated that mild hypothermia increases the incidence of serious adverse consequences including surgical site infections (12) and adverse cardiac events including ventricular tachycardia. (13,14) In trauma patients, hypothermia is associated with increased mortality. (15) Mild hypothermia inhibits platelet activation, resulting in increased blood loss. (16,17) A 2[degrees]C (3.6[degrees]F) drop in temperature increases blood loss by approximately 500 mL. (18) Mild hypothermia also alters medication metabolism and increases the duration of muscle relaxant action. (19,20) Hypothermia extends postanesthesia recovery time (21,22) and prolongs hospitalization. (12,23) The risk of these complications is considered greater for frail, elderly patients undergoing extensive surgery than it is for young, generally healthy patients undergoing comparatively minor procedures. (24)

RECOMMENDED PRACTICE I

The perioperative registered nurse should assess the patient for risk of unplanned perioperative hypothermia.

1. Perioperative registered nurses should evaluate the patient's risk for unplanned hypothermia. Sources of data include chart review, physical assessment and patient interview, and review of the anesthesia planned and the proposed surgical procedure.

2. Infancy or neonatal status should be considered.

Neonates and infants are more susceptible to hypothermia than adults because they have a high ratio of body surface area to weight, which leads to more heat loss through their skin. (6,7) Studies show that greater temperature decreases occurred in infants and neonates undergoing major surgery involving an open procedure. (7)

3. The extent and severity of a patient's traumatic injuries should be considered.

Patients with severe traumatic injuries are more likely to be hypothermic upon hospital admission and are at high risk of developing unplanned perioperative hypothermia. Between 21% and 50% of severely injured trauma patients become hypothermic. (8) Predisposing factors include exposure in the field, blood loss and shock, rapid infusions of cool fluids, removal of clothing, and impaired heat production. Hypothermia triggers a cascade of coagulopathy and acidosis. Studies have consistently found that hypothermia increases the risk of death in trauma patients. (15,25,26) In one large study more than half of the hypothermic trauma patients died. (27)