The start-up behavior of syringe and syringe pump is known to be one of the causes of inaccurate intravenous infusion. This study evaluated the method of priming the infusion system (PRIMING), and its impact on the target-controlled infusion (TCI) of two remifentanil diluents.

PRIMING was performed using an evacuation of 2.0 ml to the atmosphere prior to TCI. Forty-eight TCI, using 50 µg/ml (Remi₅₀) or 20 µg/ml (Remi₂₀) of diluents, were performed targeting 4.0 ng/ml of effect-site concentration (C_eff), with PRIMING or not. The gravimetrical measurements of the delivered infusates reproduced actual C_eff. The bolus amount and time to reach 95% target were compared.

Without PRIMING, Remi₅₀ infused less bolus (43 ± 23 %) than Remi₂₀ (19 ± 9 %) (P = 0.003), and showed more delayed increase of C_eff (11.2 ± 4.0 min) than Remi₂₀ (7.4 ± 0.4 min) (P = 0.028). However, PRIMING significantly decreased the deficit of the bolus (2 ± 1%), as well as the delay of the increase of C_eff in Remi₅₀ (1.2 ± 0.2 min) (both P < 0.001). In addition, with PRIMING, the start-up bolus showed minimal difference to the nominal bolus (1 and 2%), and C_eff were increased to 4.0 ± 0.1 ng/ml at the expected time of peak effect, irrespective of the diluents.

Proper operation of the syringe pump used in the priming of the syringe may be helpful in reduction of the inaccuracy of TCI, particularly during the early phase of infusion, or the infusion of a more concentrated diluent.