Methoxyflurane biotransformation and renal function following methoxyflurane administration for vaginal delivery or cesarean section.

Methoxyflurane (MOF) administration for conscious analgesia during vaginal delivery (range 5 to 70 min, mean 23 min) or for anesthesia following delivery of the infant at cesarean section (range 25 to 70 min, mean 44 min) was studied in 18 healthy parturients. Serum ionic fluoride increased significantly in both groups 2 hours after discontinuing MOF with peak concentrations of 11.2 and 14.1 mumol/L in the vaginal delivery and cesarean section groups, respectively. Individual peak serum ionic fluoride levels in the 2 groups of 21 and 25 mumol/L were well below reported levels for subclinical toxicity. Significant ionic fluoride elevations in fetal umbilical venous blood (mean 5.3 mumol/L) were measured in the vaginal-delivery group. Maternal urinary ionic fluoride and oxalate were elevated 24 and 48 hours postpartum. BUN, creatinine, urine volume, and urine osmolality remained within normal range. These data indicate that hazardous elevations of serum ionic fluoride with subsequent renal dysfunction are unlikely following low-dose MOF administration for vaginal delivery or cesarean section.