[1] Univ Penn, Ctr Resuscitat Sci, Philadelphia, PA 19104 USA
[2] Univ Penn, Dept Neurosurg, Philadelphia, PA 19104 USA
[3] Univ Penn, Dept Neurol, Philadelphia, PA 19104 USA
[4] Univ Penn, Dept Anesthesiol & Crit Care, Philadelphia, PA 19104 USA
[5] Univ Penn, Sect Pulm Allergy & Crit Care, Philadelphia, PA 19104 USA