Fentanyl-induced respiratory depression is attenuated in pregnant patients

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.

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 (P_ETCO₂), 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.

SpO₂ levels in the early pregnancy and postpartum groups were significantly higher and the levels of RR and P_ETCO₂ were significantly lower than the control group. RR and SpO₂ levels were significantly decreased in all groups, whereas P_ETCO₂ 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.

Pregnancy improves fentanyl-induced respiratory depression, which may be associated with the increased levels of plasma progesterone.