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

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 10 mg.ml^-1 combined with remifentanil 5 mcg.ml^-1 solution was run using a Paedfusor^® propofol target-controlled infusion model for 10 kg and 20 kg children for 57 min at a target plasma concentration of 3 mcg.ml^-1 through a 30 ml syringe, 180 cm minimum volume extension line, lever lock cannula, interlink injection site, and 22 g intravenous cannula into sample pots. Samples were taken at the completion of the loading bolus, 1 and 2 min postcompletion of loading bolus, and every 5 min 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 1 h, 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 57 min of infusion, and two different pediatric weight profiles.