• Elke Muench, Christian Bauhuf, Harry Roth, Peter Horn, Marc Phillips, Natali Marquetant, Michael Quintel, and Peter Vajkoczy.
• Departments of Anesthesiology, Klinikum Mannheim, University of Heidelberg, Mannheim, Germany.
• Crit. Care Med. 2005 Oct 1;33(10):2367-72.

ObjectiveAcute respiratory dysfunction frequently occurs following severe aneurysmal subarachnoid hemorrhage requiring positive end-expiratory pressure (PEEP) ventilation to maintain adequate oxygenation. High PEEP levels, however, may negatively affect cerebral perfusion. The goal of this study was, to examine the influence of various PEEP levels on intracranial pressure, brain tissue oxygen tension, regional cerebral blood flow, and systemic hemodynamic variables.DesignAnimal research and clinical intervention study.SettingSurgical intensive care unit of a university hospital.Subjects And PatientsExperiments were carried out in five healthy pigs, followed by a clinical investigation of ten patients suffering subarachnoid hemorrhage.InterventionsUnder continuous monitoring of intracranial pressure, brain tissue oxygen tension, regional cerebral blood flow, mean arterial pressure, and cardiac output, PEEP was applied in increments of 5 cm H2O from 5 to 25 cm H2O in the experimental part and from baseline to 20 cm H2O in the clinical part.Measurements And Main ResultsIn animals, high PEEP levels had no adverse effect on intracranial pressure, brain tissue oxygen tension, or regional cerebral blood flow. In patients with severe subarachnoid hemorrhage, stepwise elevation of PEEP resulted in a significant decrease of mean arterial pressure and regional cerebral blood flow. Analyses of covariance revealed that these changes of regional cerebral blood flow depended on mean arterial pressure changes as a result of a disturbed cerebrovascular autoregulation. Consequently, normalization of mean arterial pressure restored regional cerebral blood flow to baseline values.ConclusionsApplication of high PEEP does not impair intracranial pressure or regional cerebral blood flow per se but may indirectly affect cerebral perfusion via its negative effect on macrohemodynamic variables in case of a disturbed cerebrovascular autoregulation. Therefore, following severe subarachnoid hemorrhage, a PEEP-induced decrease of mean arterial pressure should be reversed to maintain cerebral perfusion.

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