Abstract Body: Introduction
After spontaneous intracerebral haemorrhage (ICH), a key question is the management of significant cerebral oedema, estimated to affect ~1,500 patients in the UK each year. Mannitol, an osmotic diuretic, is readily available and licensed to treat cerebral oedema. MACE-ICH will determine the feasibility of screening, assessing eligibility, approaching potential participants, randomisation, administering mannitol and completing follow-up for acute ICH patients with cerebral oedema, or at risk of cerebral oedema, to inform a definitive trial.

Methods
MACE-ICH is a multicentre, prospective, randomised, open-label, blinded-endpoint trial and will recruit adults with spontaneous ICH with estimated largest diameter >2cm, presenting within 72 hours of onset with, or at risk of cerebral oedema with or without mass effect (limited GCS score <9 (eye opening and motor only) and NIHSS>8). Participants will be randomised (1:1:1) to receive either: (a) 1g/kg 10% single-dose mannitol infusion at 10ml/min with standard care; (b) 1g/kg 10% mannitol at 10 ml/min, followed by a second dose at 24 hours (if serum osmolality <320mOsm/Kg and sodium <160mEq/L after the first dose) with standard care; or (c) standard care alone.

Results
45 participants will be recruited from ten UK, NHS hospitals providing acute stroke services. As of 17^th October 2024, 23 participants have been recruited to this study.

Conclusions
MACE-ICH will inform the design and conduct of an adequately powered, pragmatic, prospective multicentre randomised controlled trial testing mannitol as a treatment for cerebral oedema in spontaneous ICH.