Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article. Departments of Anesthesia and Pharmacology, University of Iowa Hospitals and Clinics, Iowa City, IA, USA *Address: Department of Anesthesia, 200 Hawkins Drive, University of Iowa Hospitals and Clinics, Iowa City, IA 52242, USA. Tel.: +1 319 356 7319; fax: +1 319 356 2940. E-mail address:[email protected] Submitted October 25, 2010; revised October 31, 2010; accepted November 3, 2010.