[1] Stanford Univ, Vet Affairs Palo Alto Hlth Care Syst, Sch Med, Div Pulm Allergy & Crit Care Med,Pulm Crit Care &, Palo Alto, CA USA
[2] Kaiser Oakland Med Ctr, Dept Intens Care Med, Oakland, CA USA
[3] Stanford Univ, Vet Affairs Palo Alto Hlth Care Syst, Sch Med, Div Pulm Allergy & Crit Care Med,Pulm Crit Care &, 3801 Miranda Ave Mail Code 111p, Palo Alto, CA 94304 USA