Neurocritical care
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It is frequently recommended that urine output following perioperative mannitol administration be replaced 1:1 with an isotonic crystalloid solution. It is possible that this strategy could increase brain water by reducing the serum osmolality achieved with prior mannitol administration. Therefore, brain water content of rats treated with mannitol alone or mannitol plus normal saline (NS) was studied over a range of urinary replacement ratios. ⋯ In rats, NS replacement of UO 1:1 following mannitol administration leads to brain water content no different than if NS had been given in place of mannitol. Only when the NS:UO replacement ratio was 1:3, brain water was similar to that of control animals receiving mannitol alone. The recommendation to replace UO 1:1 with an equal volume of isotonic crystalloid following perioperative mannitol administration must recognize how this strategy could elevate brain water content compared to less vigorous replacement of UO.