Comparative effect of pethidine, trichloroethylene, and Entonox on fetal and neonatal acid-base and PO2.

The second stage of labour is associated with relative fetal hypoxia and progressive metabolic acidosis. Maternal analgesia can increase the danger, especially for the high-risk fetus.In 152 patients the effect on the fetus of pethidine alone, pethidine + trichloroethylene, or pethidine + Entonox was assessed by fetal scalp blood sampling. Fetal pH, Pco(2), and Po(2) were measured and base excess was calculated. Capillary samples were also taken 45 to 60 minutes after birth in 88 of the babies to estimate the rate of neonatal recovery.Entonox proved safer than trichloroethylene, and babies treated with it maintained their Po(2) before birth, had better Apgar scores at birth, and one hour later were significantly less acidotic and much better oxygenated.