Understanding the physiological changes induced by mannitol: From the theory to the clinical practice in neuroanaesthesia

In this narrative review, the current evidence for the use of mannitol in neuroanaesthesia is presented, with focus on its pharmacokinetics and its main physiologic effects. Mannitol is a naturally occurring polyol that undergoes no biotransformation and is freely filtered in the kidney. Due to its strong osmotic effects, it induces key physiological changes, mainly in the cardiovascular system, the kidney and the brain. While it is clear that hypertonic solutions are effective in the treatment of intracranial hypertension in patients with acute brain injury, the role of mannitol in the context of intracranial haemorrhage, acute stroke and brain relaxation remains controversial. Furthermore, it possesses important side effects including acute kidney injury and electrolyte imbalances, particularly related to high doses in predisposing patients. Other aspects including the capability to modify neurological outcomes, the impact on mortality, the utility in patients with disrupted blood–brain barrier and the alternative use of hypertonic saline are also discussed. Further research is needed to make clear recommendations on these aspects.