Mark E Mikkelsen1, David F Gaieski. 1. Pulmonary, Allergy, and Critical Care Division, Department of Medicine; and, Center for Clinical Epidemiology and Biostatistics, Perelman School of Medicine of the University of, Pennsylvania, Philadelphia, PA Department of Emergency Medicine; and, Center for Resuscitation Science, Perelman School of Medicine of the University of, Pennsylvania, Philadelphia, PA.