[1] Univ Texas Southwestern Med Ctr, Dept Anesthesiol & Pain Management, Div Anesthesiol, Childrens Hlth Syst Texas, Dallas, TX 75390 USA
[2] Univ Texas Southwestern Med Ctr, Dept Pediat, Div Neonatol, Childrens Hlth Syst Texas, Dallas, TX USA
[3] Outcome Res Consortium, Cleveland, OH USA