Angiotensin Metabolite Profile After Subarachnoid Hemorrhage

Wider research context. The clinical course and neurological outcome of patients with subarachnoid hemorrhage following rupture of an intracranial aneurysm depend on surgical repair of the ruptured aneurysm to avoid rebleeding and the development of cerebral vasospasm that may cause delayed ischemic deficits. Up to 65% of patients require mechanical ventilation mostly due to neurologic deficits or hypoxia. The renin angiotensin system (RAS) is acutely activated after subarachnoid hemorrhage with increased renin and angiotensin (Ang) II plasma levels, but effects of the vasoconstrictor Ang II on development of vasospasm have not been investigated in patients. The RAS may also be activated by mechanical ventilation, but it is unknown if this has an impact on occurrence of vasospasm. Arterial hypertension is an important risk factor for subarachnoid hemorrhage and vasospasm, and around 50% of patients have a history of high blood pressure. During weaning from mechanical ventilation arterial hypertension is a wide spread clinical problem, but how RAS modifying drugs act on the angiotensin metabolite profile that may already be dysregulated after subarachnoid hemorrhage remains unclear. Objectives. To investigate associations between angiotensin metabolite profile (Ang I, Ang II, Ang 1-7 and Ang 1-5 concentrations) and angiotensin converting enzyme (ACE) and ACE2 activities in plasma as well as ACE and ACE2 activities in cerebrospinal fluid (CSF) and development of cerebral vasospasm in patients with and without mechanical ventilation following subarachnoid hemorrhage, and to find out how the angiotensin metabolite profile is changed by antihypertensive therapy with a RAS modifying drug in these patients. Methods. Ang I, Ang II, Ang 1-7 and Ang 1-5 equilibrium concentrations will be measured by liquid chromatography tandem mass spectrometry in 60 patients after subarachnoid hemorrhage in plasma. Active ACE and ACE2 concentrations will be measured in plasma and in CSF in patients with CSF drainages. Samples will be taken within 72 hours of subarachnoid hemorrhage and 7, 14 and 21 days following initial bleeding. Another plasma sample will be obtained if an antihypertensive therapy with a RAS modifying drug has been started. Angiotensin metabolite based markers of RAS enzyme activities will be calculated for renin and ACE activities and alternative RAS activation.