ObjectiveTo analyze the effect of prone position on cerebral perfusion pressure and brain tissue oxygen partial pressure in subarachnoid hemorrhage patients with acute respiratory distress syndrome (ARDS).DesignClinical study with retrospective data analysis.SettingNeurosurgical intensive care unit of a primary level university hospital.PatientsSixteen patients treated for intracranial aneurysm rupture with initial Hunt and Hess grade III or worse who developed ARDS within 2 wks after the bleeding.InterventionsRoutine neurosurgical intensive care treatment for subarachnoid hemorrhage and posthemorrhagic vasospasm including cerebral monitoring with continuous intracranial pressure and brain tissue oxygen partial pressure recordings.Measurements and Main ResultsHemodynamics, arterial oxygenation, ventilatory setting, intracranial pressure, cerebral perfusion pressure, and brain tissue oxygen partial pressure in the supine as well as in the prone position were analyzed and compared. A significant increase in Pao2from 97.3 ± 20.7 torr (mean ± sd) in the supine position to 126.6 ± 31.7 torr in the prone position was joined by a significant increase in brain tissue oxygen partial pressure from 26.8 ± 10.9 torr to 31.6 ± 12.2 torr (bothp< .0001), whereas intracranial pressure increased from 9.3 ± 5.2 mm Hg to 14.8 ± 6.7 mm Hg and cerebral perfusion pressure decreased from 73.0 ± 10.5 mm Hg to 67.7 ± 10.7 mm Hg (bothp< .0001).ConclusionsThe beneficial effect of prone positioning on cerebral tissue oxygenation by increasing arterial oxygenation appears to outweigh the expected adverse effect of prone positioning on cerebral tissue oxygenation by decreasing cerebral perfusion pressure in ARDS patients.