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Mild Hypothermia For Cerebral Protection In Aortic Arch Surgery: A Meta Analysis
Navneet Singh;
Auckland City Hospital, Auckland, New Zealand
BACKGROUND: Open thoracic aortic surgery remains the mainstay of treatment for type A aortic dissections and aortic arch aneurysms. These operations are being increasingly performed in a minimally-invasive fashion (hemisternotomies or mini-sternotomies). In order to provide neurological protection when operating on the aortic arch and its corresponding head and neck vessels, hypothermia is commonly used intraoperatively to reduce cerebral metabolic demand and minimise the impacts resulting from temporarily-reduced intracerebral blood flow. Most centres use moderate (20 - 28
oC) or deep (14 - 20
oC) hypothermic circulatory arrest for this purpose. However, these low temperatures are known to have negative consequences on visceral organ function and coagulopathy. Ultimately, there is no clear consensus in the literature on the optimum temperature management strategy for brain protection in aortic surgery. We hence aimed to investigate whether mild hypothermia (>28
oC) achieves acceptable postoperative neurological outcomes (stroke rates) as compared to moderate hypothermia during aortic arch surgery.
METHODS: A systematic review and meta-analysis of all randomised and non-randomised studies investigating the above study aim was undertaken as per the PRISMA guidelines. Review Manager 5.4 software was utilised for statistical analyses.
RESULTS: Nine observational studies met inclusion criteria with a total sample size of 1357 patients. No randomised controlled trials were available on this topic. Most studies comprised of aortic dissection repairs, with a sizeable proportion being conducted in a minimally-invasive fashion. Mild hypothermia (with selective cerebral perfusion) correlated with statistically significantly reduced postoperative permanent neurological dysfunction (strokes) as compared to moderate hypothermia (odds ratio 0.39, 95% confidence interval 0.24 - 0.64, p = 0.0001). Mild hypothermia also correlated with significantly reduced rates of postoperative acute renal failure (odds ratio 0.51, 95% confidence interval 0.33 - 0.80, p = 0.003). There was no significant difference in bleeding rates.
CONCLUSIONS: Mild hypothermia - in conjunction with selective cerebral perfusion - may be a safe alternative to moderate hypothermia for providing neurological protection during circulatory arrest in aortic arch surgery. However, robust randomised data is required to corroborate this theory. Future research must also focus on the implications of altering cerebral protection strategies on minimally-invasive approaches for aortic surgery.
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