1 Department of Anesthesiology, Duke University Medical Center, Durham, NC 27710, USA. Electronic address: wel12@duke.edu.
2 Department of Anesthesiology, Duke University Medical Center, Durham, NC 27710, USA.
3 Department of Anesthesiology, Duke University Medical Center, Durham, NC 27710, USA; Women's Anesthesia Division, Department of Anesthesiology, Duke University Medical Center, Durham, NC 27710, USA.