Fentanyl-induced respiratory depression is attenuated in pregnant patients

Background Respiratory depression is a complication of intravenous fentanyl administration. The effect of pregnancy on respiratory depression following opioid administration is unclear. This study investigated the effect of pregnancy on fentanyl-induced respiratory depression. Patients and methods Female patients were divided into three groups (n=20 per group): control group (non-pregnant and scheduled for laparoscopic surgery), early pregnancy group (pregnant for 45-60 days and scheduled for abortion), and postpartum group (5-7 days postpartum scheduled for complete curettage of uterine cavity). All patients received an intravenous infusion of fentanyl 2 μg/kg. Respiratory rate (RR), end-tidal pressure of carbon dioxide (PETCO2), and pulse oxygen saturation (SpO2) were recorded continuously from just before fentanyl infusion to 15 min after commencing infusion. Plasma levels of progesterone were measured. Results SpO2 levels in the early pregnancy and postpartum groups were significantly higher and the levels of RR and PETCO2 were significantly lower than the control group. RR and SpO2 levels were significantly decreased in all groups, whereas PETCO2 was significantly increased after fentanyl infusion. The rates of RR increase and SpO2 decrease were significantly faster in the control group than in the other groups. The lowest SpO2 after intravenous fentanyl administration was significantly positively correlated with plasma progesterone levels. Conclusion Pregnancy improves fentanyl-induced respiratory depression, which may be associated with the increased levels of plasma progesterone.