The effect of labor on sevoflurane requirements during cesarean delivery

Abstract

Background Labor results in the release of sensitizing substances such as progesterone, prostaglandins, cytokines and cortisol, some of which have been observed to participate in sleep regulation. We hypothesized that these substances could affect sleep regulation and therefore the amount of volatile agent required to provide general anesthesia for cesarean delivery. Methods A total of 50 patients were enrolled, of whom 25 had uterine activity less than 30 Montevideo units (Prelabor group) and 25 had uterine activity greater than 80 Montevideo units (Labor group). Anesthesia was maintained with 50% oxygen in nitrous oxide with sevoflurane. Sevoflurane concentration was adjusted to sustain a constant Bispectral Index (BIS) value of 40–55. Prolactin, progesterone and cortisol levels were evaluated immediately before cesarean delivery. Results End-tidal concentrations of sevoflurane in the Prelabor group were higher than in the Labor group with similar Bispectral Index values. No significant differences were found in prolactin, progesterone and cortisol levels between the two groups. Conclusion Anesthetic requirements for sevoflurane, as measured by Bispectral Index, decrease in laboring versus non-laboring parturients undergoing cesarean delivery. Prolactin, progesterone and cortisol do not appear to be responsible for this observation.