Clazosentan (CLA) reduces cerebral vasospasm after aneurysmal subarachnoid hemorrhage (aSAH). However, adverse events including pulmonary edema were reported. We examined whether the strict management of fluid balance reduces the adverse events and improves patient outcomes.

Patients with aSAH between 2020 and 2023 were included. They were divided into pre-CLA (before CLA approval) and post-CLA (after approval) groups. The patients in the post-CLA group were further divided into the post-CLA1 (before the change in fluid management) and post-CLA2 (after the change) groups. To achieve fluid balance of 0–500 ml/day according to the modified protocol, the infusion volume was restricted.

The daily fluid balance increased from the pre-CLA to the post-CLA1 periods (p = 0.01). The protocol changes decreased the pulmonary edema (post-CLA1 vs. post-CLA2, 44 vs. 22 %, p = 0.09) and discontinuation of CLA (44 vs. 9 %, p < 0.01). The incidence of symptomatic spasm (SS) and delayed cerebral infarction (DCI) in the post-CLA2 were slightly reduced without significant differences (SS: 17 vs. 13 %, p = 0.69; DCI: 11 vs. 9 %, p = 1.00).

Strict management of fluid balance during CLA treatment reduced the adverse events and discontinuation of CLA administration. Fluid restriction may positively affect the management of cerebral vasospasms.