Background <p>Vasospasms are common in patients presenting with non-traumatic subarachnoid haemorrhage (SAH) and are the main contributor to long-term disability or death in these patients. The key immediate management of vasospasms is the improvement of brain perfusion by the administration of intravenous fluid and vasopressors if needed. Yet, there is no clear recommendation regarding the choice of fluid in this particular patient population. Data suggests a survival benefit using normal saline in patients with TBI; however, its impact on outcomes in patients with SAH is lacking. Thus, the aim of this study is to evaluate whether the use of normal saline reduces clinically relevant vasospasms compared to Ringer’s lactate in patients with SAH.</p> Methods <p>Patients presenting with non-traumatic SAH will be randomised 1:1 to normal saline or Ringer’s lactate group. Blinded study fluid will be used exclusively for resuscitation and maintenance until ICU/IMC discharge or a maximum of 14&#xa0;days, whichever occurs first. Management of vasospasms and general management of the SAH patient will be according to the clinic standard of care. Primary endpoint is the occurrence of clinically relevant vasospasms. Key secondary outcomes include mortality, severity and treatment of vasospasms, and neurological outcomes at 90&#xa0;days.</p> Discussion <p>The proposed randomised controlled trial offers a safe, non-invasive way to gain insights about crystalloid fluid choice in SAH patients, with potential to improve outcomes in this critically ill patient group. This study could establish a new gold standard in fluid therapy for neuro-critical care.</p> Trial registration <p>The trial is registered on ClinicalTrials.gov (date of registration 18 June 2021) and on the Swiss National Clinical Trials Portal, SNCTP000004575.</p>