Adsorption of sufentanil to epidural filters and catheters

Background and objective: Stable drug concentrations must be administered to provide adequate patient-controlled epidural analgesia. This study investigated the stability of sufentanil after the epidural delivery system had been flushed with solutions containing the drug. Methods: Sufentanil citrate, 5 pg mL -1 was injected through an epidural catheter system into a glass container. The concentrations of the drug leaving the system, in 1 mL aliquots (1-5 mL) were measured using high-performance liquid chromatography. In the same manner, sufentanil samples were analysed after flushing the filter, as well as after priming the filter and catheter. Results: ANOVA for repeated measurements demonstrated that sufentanil concentrations remained constant as long as the catheter had been adequately flushed. However, the concentration of sufentanil in the solution exiting the filter was reduced significantly. Hardly any sufentanil could be detected (0.09 ± 0.01 μg mL -1 , P 0.05). The greatest decrease occurred when the whole epidural delivery apparatus (catheter and filter) was primed; to regain baseline values, as much as 4 mL solution was needed to flush the system. Conclusions: Sufentanil citrate is adsorbed by the materials used to manufacture systems (catheters, filters) used in epidural anaesthesia. Hence, the epidural catheter system should be primed with sufentanil before connecting it to the patient so as to deliver reliable concentrations.