In clinical practice, pregnant women have lower anesthetic requirements for general anesthesia than nonpregnant women. This effect has been well studied in animals (mice & rabbits) as well as in different phases of the human menstrual cycle. Progesterone concentration is lower in early pregnancy than term pregnancy, declines rapidly after delivery, and returns to normal values within 72 hours postpartum. Nonetheless, the specific association between anesthetic or analgesic requirements and plasma concentration of progesterone in full-term parturients has not been studied in detail.
Dr. Seonghoon Ko, Department of Anesthesiology and Pain Medicine and Research Institute of Clinical Medicine, Chonbuk National University Medical School and Hospital, Jeonju, Korea, and colleagues, sought to identify relationships between anesthetic or analgesic requirements and maternal serum concentrations of progesterone in 100 parturients >36 weeks’ gestation scheduled for planned cesarean delivery under general anesthesia. The results of their study are published in this month’s issue of Anesthesia & Analgesia in the article titled “The Relationship Between Serum Progesterone Concentration and Anesthetic and Analgesic Requirements: A Prospective Observational Study of Parturients Undergoing Cesarean Delivery.”
Serum progesterone was measured in venous blood collected from parturients just before the induction of anesthesia. An anesthesiologist blinded to progesterone concentration managed the general anesthetic. The obstetricians performed the Cesarean Section using a Pfannenstiel incision with in situ uterine repair. The depth of general anesthesia was monitored using the bispectral index (BIS). The BIS was maintained between 40 and 60. Sevoflurane volume per hour of anesthesia was calculated and cumulative sevoflurane consumption was recorded. All patients were interviewed using the Brice questionnaire to assess intraoperative awareness at 6 to 8 hours after PACU discharge and again the following day.
The authors found that the serum concentration of progesterone was inversely correlated with sevoflurane consumption per hour. Specifically, women with relatively higher progesterone levels had lower sevoflurane consumption per hour (P = 0.02), as well as less cumulative analgesic consumption (P = 0.02) 48-hours after the procedure.. They concluded that elevated serum progesterone concentration may decrease anesthetic and analgesic requirements of near full-term parturients, a finding consistent with our understanding of the neurobiology of progesterone.
There are some limitations to this study. First, the study did not consider diurnal fluctuation of progesterone concentration. Second, pregnancy involves many hormonal changes, including changes in estrogen, human chorionic gonadotropin, and endogenous opioids. These hormones were not studied, and may have mediated the effects inversely correlated with progesterone in this study.