Mild hypothermia during intercranial aneurysm surgery

AORN Journal,  July, 2007  by George Allen

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New England Journal of Medicine January 2005

Postoperative complications including new neurological deficits are common after intracranial vascular surgery as a result of factors such as brain retraction, vessel occlusion, and intraoperative hemorrhage. Use of systemic hypothermia as a protective mechanism in neurosurgery was first reported in 1957, but the strategy was abandoned during the 1970s and 1980s. Interest in this approach was rekindled after it was demonstrated in the laboratory that mild hypothermia (ie, a temperature of approximately 33[degrees]C to 35[degrees]C [91.4[degrees]F to 95[degrees]F]) improved the outcome of ischemic and traumatic insults, a finding that coincided with researchers studying the use of hypothermia for treatment of other neurological disorders, including head trauma, stroke, and cardiac arrest. Despite surveys showing that hypothermia is used in more than 50% of surgical procedures for aneurysms, however, there is little information available concerning the effects of hypothermia on the outcome of neurovascular surgery. The objective of this randomized, prospective, multicenter study was to determine whether intraoperative cooling (ie, to a target temperature of 33[degrees]C [91[degrees]F) versus maintaining normothermia (ie, a target temperature of 36.5[degrees]C [97[degrees]F]) during open craniotomy would improve outcomes among patients with acute, aneurismal, subarachnoid hemorrhage.

Patients who had a subarachnoid hemorrhage from a radiologically demonstrated intracranial aneurysm no more than 14 days before a planned surgery for aneurysm clipping were included in the study if they

* were not pregnant;

* were at least 18 years of age;

* had a World Federation of Neurological Surgeons score of I, II, or III (ie, a "good grade"); and

* had a Rankin score of zero (ie, no neurological disability) or one (ie, mild disability) before hemorrhage.

Patients were excluded if they had a body mass index (BMI) of more than 35, had a cold-related disorder, or had an endotracheal tube in place.

Patients were randomly assigned to either the hypothermia group or the normothermia group. Anesthesia was induced with thiopental or etomidate, and standard monitors were used. Each patient's temperature was monitored in the retrocardiac esophagus, and the patient was covered with a forced-air blanket connected to a heating-cooling unit. The temperature of the patients assigned to the normothermia group was kept between 36[degrees]C and 37[degrees]C (96.8[degrees]F and 98.6[degrees]F). For patients assigned to the hypothermia group, esophageal temperature was reduced as quickly as possible, with the goal of achieving a temperature between 32.5[degrees]C and 33.5[degrees]C (90.5[degrees]F and 92.3[degrees]F) by the time the first clip was applied. Rewarming of patients assigned to the hypothermia group began after the last aneurysm clip had been secured. Patients were extubated when they were deemed ready.

Detailed daily records on patients' conditions were collected until discharge or for 14 days after surgery. Patients were evaluated approximately 90 days after surgery by a certified examiner and a neuropsychologist using the Glasgow Outcome Scale, the Rankin Scale, the Barthel Index, the National Institutes of Health Stroke Scale, and a battery of neuropsychological examinations. A total of 106 predefined adverse events or procedures were monitored, including neurological injury, myocardial dysfunction, coagulation, and infection. Common statistical procedures, including the Student's t test, the Wilcoxon signed rank test, and the Fisher exact test, were used to analyze differences between the two groups.

FINDINGS. Between February 2000 and April 2003, a total of 3,966 patients underwent aneurysm surgery at 30 participating centers. Of the 1,183 patients who met the inclusion criteria, 1,000 were enrolled and completed the study, with 499 in the hypothermia group and 501 in the normothermia group. There was no significant difference in the number of adverse events between the two groups, including the duration of stay in the ICU; the total length of hospitalization; the rate of death at follow up (ie, 6% in both groups); or the destination at discharge (ie, home or another hospital). In both groups, the median time to the final outcome assessment was 88 days (10th and 90th percentiles, 72 and 113 days). Of the 499 patients in the hypothermia group, 329 had a Glasgow Outcome Score of 1 (ie, good outcome) compared with 314 of 501 patients in the normothermia group (66% versus 63%; odds ratio 1.14, 95% confidence interval 0.88 to 1.48, P = .32). Postoperative bacteremia was more common in the hypothermia group than in the normothermia group (5% versus 3%, P = .05).

CLINICAL IMPLICATIONS. The result of this study demonstrated that intraoperative hypothermia (ie, a temperature between 32.5 and 33.5[degrees]C [90.5[degrees]F and 92.3[degrees]F]) did not improve the neurological outcome after craniotomy in patients with aneurismal, subarachnoid hemorrhage. Perioperative nurses should understand that intraoperative hypothermia does not appear to have any beneficial effect on the outcome of open craniotomy surgery, and they should continue to maintain normothermia in this patient population.