1 Department of Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
2 University of Saskatchewan, Respirology, Critical Care and Sleep Medicine, Saskatoon, Saskatchewan, Canada.
3 Division of Pulmonary and Critical Care, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
4 Division of Pulmonary and Critical Care, David Geffen School of Medicine at UCLA, Los Angeles, CA, USA. Electronic address: IBarjaktarevic@mednet.ucla.edu.