Hotly debated topics in obstetric anesthesiology 2008: a theory of relativity.

This paper reviews and discusses three controversial subjects regarding treatment of intraoperative nausea and other complications experienced by patients undergoing cesarean delivery under spinal anesthesia: (1) the administration of supplemental oxygen, (2) prophylactic vasopressors and (3) the use of low-dose combined spinal epidural anesthesia (CSE). While not universally acknowledged, recent data suggest that the routine administration of supplemental oxygen to normal-weight, healthy patients undergoing elective cesarean delivery is unnecessary, especially when spinal hypotension is minimized. Supplemental oxygen administration does not prevent intraoperative or postoperative nausea and vomiting. Additionally, although higher inspired oxygen fractions modestly increase fetal oxygenation, they also cause a concomitant increase in oxygen free radical activity in both mother and fetus, which may weaken the infant's ability to withstand subsequent neonatal insult. The use of prophylactic vasopressor infusions may benefit some patients, but parenteral preanesthetic ephedrine administration is not warranted. Heart rate variability guided therapy could help identify patients at risk for developing severe hypotension after spinal anesthesia. High-dose phenylephrine infusion in conjunction with rapid co-hydration is efficient, but is unfortunately associated with a relatively high incidence of maternal bradycardia. Oxygen, fluid administration and prophylactic vasopressors may not be the solution to hypotension, nausea and vomiting associated with spinal anesthesia during cesarean delivery. Lower dose spinal anesthesia as part of a CSE technique reduces the incidence of maternal hypotension, and in our opinion is the best option currently available.