Perioperative hypothermia and risk of cancer metastasis

AORN Journal, July, 2007 by George Allen

the American Journal of Surgery June 2005

Resistance to cancer metastasis is mediated by host immunity. Consequently, perioperative factors that impair host immunity are likely to facilitate the establishment of metastatic tumor during cancer surgery. Perioperative factors including surgery itself; anesthetic medications, most of which are immunosuppressive; mechanical ventilation; and mild hypothermia all impair immune function. Results of in vitro studies suggest that mild core hypothermia directly impairs natural host defenses. In particular, leukocyte mobility and phagocytosis, T-cell-mediated antibody production, and neutrophil function are impaired, resulting in an increased risk of surgical site infections (SSIs). Similarly, immune suppression caused by mild perioperative hypothermia may augment the risk of tumor metastases during cancer surgery.

The purpose of this study was to test the hypothesis that hypothermia-induced immune suppression sufficient to triple the incidence of SSI also augments the risk of colon cancer recurrence and subsequent mortality. This study was a follow-up to a previously published study that evaluated the effects of mild hypothermia (ie, 34.5[degrees]C [94.1[degrees]F]) on the risk of SSI. The major conclusion of that study was that 2[degrees]C (3.6[degrees]F) of intraoperative hypothermia resulted in a threefold increase in the risk of SSI.

Patients between the ages of 18 and 80 years undergoing elective colorectal resection for cancer or inflammatory bowel disease were included in the study. Exclusion criteria were use of steroids or other immunosuppressive medications, including cancer chemotherapy, within four weeks of surgery; a recent history of fever, infection, or both; serious malnutrition (ie, serum albumin less than 3.3 mg/dL, white blood count less than 2,500 cells/mL, or higher than 20% weight loss); or bowel obstruction.

At the time of induction, patients were randomly assigned to one of two temperature management groups:

* the normothermic group, in which the patient's core temperature was maintained near 36.5[degrees]C (97.7[degrees]F), or

* the hypothermic group, in which the patient's core temperature was allowed to decrease to approximately 34.5[degrees]C (94.1[degrees]F).

Antibiotic treatment, fluid management, and anesthesia induction were standardized in both groups. Intravenous fluid was administered by a fluid warmer, but the warmer was only activated in patients assigned to extra warming. Similarly, a forced-air cover was positioned over the upper body and was set to deliver ambient air in the hypothermic group and air at 40[degrees]C (104[degrees]F) in the normothermic group. Follow-up was restricted to patients who received a diagnosis of cancer.

Among the 200 patients enrolled in the original study between July 1993 and March 1995, 140 patients had a diagnosis of cancer. Outcomes for these patients were evaluated between August 2001 and June 2002, providing between five and nine years of follow-up. The medical records were reviewed to determine patient outcomes, including cancer-free interval, recurrence of cancer, and mortality. The primary outcome measures were tumor recurrence and all causes of mortality. Common statistical techniques, including the Student t test, chi-square test, and the Wilcoxon signed rank test, were used to analyze differences between the groups.

FINDINGS. The analysis was restricted to 124 cancer patients for whom follow-up data were available. There was no difference between the hypothermic and normothermic groups in the number of patients who developed recurrent tumor (P = .482) or in patients' cancer-free intervals between the groups (P = .920). In addition, there was no difference in the cancer-free survival between the groups (P = .498) and no statistically significant differences in cancer-related mortality (P = .891) or total mortality (P = .470) between the normothermic and hypothermic groups.

CLINICAL IMPLICATIONS. The results of this study revealed that although mild hypothermia impaired immune function in cancer surgery patients, it did not increase the incidence of recurrent tumor, cancer death, or all-cause mortality. Perioperative nurses should understand that the results of this study suggest that the risk of perioperative cancer dissemination is primarily determined by factors other than hypothermia-induced inhibition of immune function.

Yucel Y, Barlan M, Lenhardt R, Kurz A, Sessler DI. Perioperative hypothermia does not enhance the risk of cancer dissemination. Am J Surg. 2005;189(6): 651-655.

GEORGE ALLEN

PHD, RN, CNOR, CIC

DIRECTOR OF INFECTION CONTROL

DOWNSTATE MEDICAL CENTER

BROOKLYN, NY