Abstract: We included three studies, enrolling 1158 participants. Each study reported an increased rate of recovery with intraoperative mild hypothermia, but the effect sizes were not sufficient for certainty. A total of 1086 of the 1158 participants (93.8%) had good grade aneurysmal subarachnoid haemorrhage. Seventy-six of 577 participants (13.1%) who received hypothermia and 93 of 581 participants (16.0%) who did not receive hypothermia were dead or dependent (RR 0.82; 95% CI 0.62 to 1.09; RD -0.03; 95% CI -0.07 to 0.01, moderate-quality evidence) after three months. Reported unfavourable outcomes did not differ between participants with or without hypothermia. The quality of evidence for these outcomes remains unclear because the outcomes were reported in a variety of ways. No decompressive craniectomy or corticectomy was reported. Thirty-six of 577 (6.2%) participants with hypothermia and 40 of 581 (6.9%) participants without hypothermia had infarction. Thirty-four of 577 (6%) participants with hypothermia and 32 of the 581 (5.5%) participants without hypothermia had clinical vasospasm (temporary deficits). Duration of hospital stay was not reported. Only one study with 112 participants reported discharge destinations: 43 of 55 (78.2%) participants with hypothermia and 39 of 57 (68.4%) participants in the control group were discharged home. The remaining participants were discharged to other facilities. Thirty-nine of 577 (6.8%) participants with hypothermia and 39 of 581 (6.7%) participants without hypothermia had infections. Six of 577 (1%) participants with hypothermia and 6 of 581 (1%) participants without hypothermia had cardiac arrhythmia. It remains possible that intraoperative mild hypothermia could prevent death or dependency in activities of daily living in people with good grade aneurysmal subarachnoid haemorrhage. However, the confidence intervals around this estimate include the possibility of both benefit and harm. There was insufficient information to draw any conclusions about the effects of intraoperative mild hypothermia in people with poor grade aneurysmal subarachnoid haemorrhage or without subarachnoid haemorrhage. We did not identify any reliable evidence to support the routine use of intraoperative mild hypothermia. A high-quality randomised clinical trial of intraoperative mild hypothermia for postoperative neurological deficits in people with poor grade aneurysmal subarachnoid haemorrhage might be feasible.

Plain-language summary: The updated evidence is current to August 2015. We found only three appropriate studies with a total of 1158 participants to include. Data primarily came from one high-quality study with 1000 participants. Our analysis showed that in good grade patients, it remains possible that cooling the brain during surgery might prevent death or dependency in everyday activities. Very limited information was available for those without bleeding or those with poor grade bleeding. Unfavourable outcomes did not differ between participants with or without hypothermia. The quality of evidence for these outcomes remains unclear because they were reported in a variety of ways. We do not have enough data to be certain about the effect of cooling on death or dependency. The evidence for other outcomes was more uncertain, since we could not combine the data due to variation in the definition and reporting of outcome data. Data in our analyses were primarily from one high quality trial on good grade participants.