Time dependency of the ratio of umbilical vein/maternal artery concentrations of vecuronium in caesarean section

Background: The ratio of umbilical vein (UV) and maternal artery (MA) concentrations of vecuronium may more accurately determine the placental transfer ratio during caesarean section. This ratio potentially correlates with the time from induction of anaesthesia to delivery (I-D time). The aim of this study was to determine the UV/MA ratio of vecuronium and its relationship with the I-D time. Methods: Eighteen pregnant women at full term undergoing caesarean section were studied. The parturient was given intravenously 0.01 mg/kg vecuronium as a priming dose, followed 180 s later by 0.11 mg/kg vecuronium as an intubation dose and 4 mg/kg thiamylal. The time from the injection of the intubation dose to the clamping of the umbilical cord was regarded as the I-D time. At the time of clamping the umbilical cord, blood samples were collected and the UV and MA of vecuronium were measured. Results: The UV/MA ratio and the I-D time, expressed as the mean (SD), were 0.056 (0.016) and 280 (57) s, respectively. The regression equation indicated y=0.0083+0.00017×(R2=0.381, r=0.617, P=0.0063, I-D time (s)=x, UV/MA=y). Conclusion: The present study demonstrated that the UV/MA ratio of vecuronium as an index of the placental transfer becomes smaller as the delivery time after injection of this drug becomes shorter during caesarean section.