Consistency of remifentanil concentrations in propofol-Remifentanil infusions. A laboratory-based study.

Abstract

There is increasing interest in two-agent single-pump intravenous infusions for anesthesia and sedation in pediatric patients. Propofol-remifentanil is one such mixture. The poor miscibility of such admixtures when remifentanil is added in very high concentrations and when the admixtures are maintained in static conditions has been demonstrated; however, these physiochemical properties have not been examined in clinically relevant concentrations or settings. To examine if propofol-remifentanil admixtures maintain consistent remifentanil delivery when mixed in clinically relevant remifentanil concentrations and subjected to the physical effects of an actively infusing, directly-engaged syringe driver system with an extension line, as occurs when propofol-remifentanil is administered to a patient. A propofol 10mg.ml-1 combined with remifentanil 5 mcg.ml-1 solution was run using a Paedfusor® propofol target-controlled infusion model for 10kg and 20kg children for 57min at a target plasma concentration of 3 mcg.ml-1 through a 30ml syringe, 180cm minimum volume extension line, lever lock cannula, interlink injection site, and 22g intravenous cannula into sample pots. Samples were taken at the completion of the loading bolus, 1 and 2min postcompletion of loading bolus, and every 5min thereafter. The remifentanil concentration in these samples was then assayed using chromatography. There was no difference in the concentration of remifentanil in the samples based on the duration of infusion to the endpoint of 1h, or on the patient weight model used. The concentration remained 5 mcg.ml-1 +/- 0.5 mcg.ml-1 per sample. The measurement uncertainty for the assay at 0.5 mcg.ml-1 is +/- 0.2 mcg.ml-1 . The concentration of remifentanil was 5 mcg.ml-1 +/- 0.5 mcg.ml-1 and was consistent across 57min of infusion, and two different pediatric weight profiles.