1. Assistant Professor of Anesthesiology, Mayo Graduate School of Medicine.
2. Assistant Professor of Laboratory Medicine and Pathology, Mayo Graduate School of Medicine.
3. Statistician, Biostatistics, Mayo Clinic, Rochester, Minnesota.
4. Professor of Surgery, Mayo Graduate School of Medicine. Received from the Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota. Submitted for publication January 27, 1999. Accepted for publication October 7, 1999. Supported by a Bayer Corporation 1995 Research Grant and the Mayo Foundation for Medical Education and Research, Rochester, Minnesota. Presented at the annual meeting of the