Low dose mannitol versus high dose mannitol to achieve brain relaxation in brain tumor surgery: a meta-analysis

Background: Brain edema is one of the common intraoperative problems in neurosurgery. Brain edema is usually treated by administering a hypertonic solution such as mannitol. Some studies mentioned the use of high-dose mannitol (> 1 g/kg), but it is important to note that mannitol has several drawbacks. This meta-analysis aims to identify the most effective mannitol dose to reduce intraoperative brain edema among brain tumor cases. Methods: We searched for all randomized-controlled trials (RCTs) published in English, which compared various doses of mannitol for brain tumors published between 2010 - 2020. The studies should include adult patients with intracranial tumors who received mannitol to reduce brain edema before opening the dura mater. The primary and secondary outcomes are satisfactory brain relaxation and the need for additional treatment to achieve adequate relaxation, respectively. Result: Three RCTs were identified using an agreed-upon search strategy. A total of 354 patients were included in the metaanalysis. Satisfactory brain relaxation occurred in 70 of 152 and 154 of 202 patients who received low-dose and high-dose mannitol, respectively (RR 0.64 (95% CI, 0.48 - 0.86, p=0.003). There were 59 of 152 and 71 of 202 patients who needed additional treatment to make the brain adequately relax (RR 1.33, 95 % CI 0.97 - 1.83, p=0.08). Conclusion: A mannitol dose of >= 1g/kg achieves better brain relaxation. And it required fewer additional measures to relax the brain. These conclusions are drawn from low-quality evidence. Further research on the safety of high-dose mannitol is warranted to ensure its benefit outweighs its harm.