Inorganic fluoride levels in parturients and neonates following methoxyflurane analgesia during labor and delivery

Serum inorganic fluoride (SIF) levels after administration of intermittent methoxyflurane (MOF) analgesia (mean 104.8 min) during labor and of continuous MOF analgesia (mean 22.9 min) during delivery in 36 parturients and their neonates were compared with values in 10 mothers and neonates given extended epidural blocks for labor and delivery. Levels were determined pre-MOF, at delivery, and at 2, 12, 24, and 48 hours postpartum. The highest maternal level (mean 18,7 μM/L) occurred 2 hours after delivery, but decreased significantly thereafter. In contrast, control mothers had a mean level of 2.37 μM/L and remained essentially unchanged. The mean level in neonates exposed to MOF was 11.95 μM/L, while the mean control neonatal cord blood level was 2.22 μM/L. The SIF level decreased to 5.963 μM/L 12 hours after delivery and remained essentially the same up to 48 hours postpartum. The mean urine volume collected from the neonates during the first 24 hours was 23.14 ml, while the fluoride level was 43.13 μM/L. On the 2nd day after delivery, mean urine volume was 47.91 ml, with a fluoride concentration of 39.05 μM/L. These findings support previous findings that, following MOF analgesia, the peak rise in mean maternal fluoride level occurs approximately 2 hours after delivery, a level far lower than reported nephrotoxic levels. The study also indicates that neonates are capable of excreting fluoride.