Postoperative hypothermia—the chilling consequences

AORN Journal,  May, 2006  by Kelly K. Good,  Jill A. Verble,  Janet Secrest,  Barbara R. Norwood

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The article "Postoperative hypothermia--The chilling consequences" is the basis for this AORN Journal independent study. The behavioral objectives and examination for this program were prepared by Rebecca Holm, RN, MSN, CNOR, clinical editor, with consultation from Susan Bakewell, RN, MS, BC, education program professional, Center for Perioperative Education.

Participants receive feedback on incorrect answers. Each applicant who successfully completes this study will receive a certificate of completion. The deadline for submitting this study is May 31, 2009.

Complete the examination answer sheet and learner evaluation found on pages 1069-1070 and mail with appropriate fee to

AORN Customer Service

c/o Home Study Program

2170 S Parker Rd, Suite 300

Denver, CO 80231-5711

or fax the information with a credit card number to (303) 750-3212.

You also may access this Home Study via AORN Online at http://www.aorn.org/journal/homestudy/default.htm.

BEHAVIORAL OBJECTIVES

After reading and studying the article on postoperative hypothermia, nurses will be able to

1. discuss the physiology of normothermia,

2. describe the implications of hypothermia,

3. identify methods of preventing postoperative hypothermia, and

4. explain Roy's Adaptation Model as it applies to unintended hypothermia.

This program meets criteria for CNOR and CRNFA recertification, as well as other continuing education requirements.

A minimum score of 70% on the multiple-choice examination is necessary to earn 3.1 contact hours for this independent study.

Purpose/Goal: To educate perioperative nurses about the consequences of postoperative hypothermia and methods of prevention.

Hypothermia, defined as a core body temperature of lower than 36[degrees]C (96.8[degrees]F), (1) is a common problem for patients undergoing surgery. Nurses have contributed to the literature on hypothermia, particularly in the area of shivering and treatment modalities. Much of the research demonstrating the direct physiological effects of hypothermia, however, is found in the medical literature. This article reviews research on the physiological effects of postoperative hypothermia, offering nurses additional evidence to support interventions for temperature correction in patients with hypothermia. Clinical practice guidelines for prevention and treatment of postoperative hypothermia are provided. Current research on effective re-warming measures also is discussed.

PHYSIOLOGY OF NORMOTHERMIA

Body temperature is the result of a balance between heat production and heat loss. Heat is a byproduct of the body's natural metabolic processes, but as it is produced, it also is lost to the environment. Regulation of body temperature occurs through a negative feedback system in the central nervous system, primarily the hypothalamus. The hypothalamus acts as a thermostat, and as changes in body temperature occur, it initiates heat-increasing vasoconstriction or heat-decreasing vasodilatation. As a result, body temperature is maintained within a normal range, ensuring a constant rate of metabolism, enhanced nervous system conduction, and optimal skeletal muscle contraction. (1)

PATHOPHYSIOLOGY OF PERIOPERATIVE HYPOTHERMIA

Hypothermia has long been recognized as problematic during the perioperative period. Events that can decrease body temperature during surgery include

* a cold OR environment,

* administration of unwarmed IV fluids,

* medication-induced vasodilatation,

* decreased basal metabolic rate,

* anesthetic-induced impairment of the hypothalamic thermostat,

* exposure of body cavities to room temperature air, and

* loss of heat from the lungs when warm air in the lungs is mixed with unwarmed inhaled gases.

In addition, general anesthesia lowers the threshold for vasoconstriction, which normally protects the body from hypothermia. This causes a 1[degrees]C to 5[degrees]C (1.8[degrees]F to 9[degres]F) decrease in core body temperature during the first hour of general anesthesia.' This decrease is caused by redistribution of heat from the warmer core to the periphery. (2) Intravenous fluids that are not warmed and are administered at room temperature during surgery cause a decrease in mean body temperature of approximately 0.25[degrees]C (0.35[degrees]F). (2) Hypothermia can increase the length of stay in the postanesthesia care unit (PACU) and is identified as one of the most frequent adverse outcomes in the immediate postoperative period. (2)

IMPLICATIONS OF POSTOPERATIVE HYPOTHERMIA

It has long been apparent that patients' body temperatures drop when patients are undergoing general anesthesia. Recognizing that patients whose body temperatures are decreased often experience higher incidences of complications in the postoperative period led to some of the initial research on hypothermia. A number of physiologic changes occur in the body with a drop in core body temperature below 36[degrees]C (96.8[degrees]F). Table 1 summarizes the causes and physiological consequences of perioperative hypothermia. Nurses play a pivotal role in preventing hypothermia and intervening for patients with hypothermia to minimize the physiological effects as well as to provide comfort.