The effect of air within the infusion syringe on drug delivery of syringe pump infusion systems

Application of highly concentrated short-acting vasoactive drugs in the critically ill patient requires precisely working syringe pump systems for continuous intravenous drug delivery. We performed a bench study to investigate the consequences of small amounts of air entrapped within a 50-ml infusion syringe. In particular we studied the effect of entrapped air on drug delivery after moderate vertical displacement of the pump by 50 cm (e. g, in preparation for transport) and the effect on the time required to trigger the pressure alarm after occlusion of the infusion line. At a flow rate of 1 ml/h,lowering the syringe pump prolonged the zero-drug delivery time from (mean+/-SD) 4.1+/-0.8 min (without air) to 6.2+/-0.9 (with 1 mi air) and to 13.1+/-0.9 min (with 2 mi of air, p<0.001 for all comparisons). Entrapping of 2 mi of air within the syringe resulted in a 2.6-fold prolongation of the occlusion alarm time after accidental occlusion of the infusion line and a 3-fold increase of the resulting infusion bolus after occlusion. Enclosed air within infusion syringes considerably affects the syringe compliance. It increases the susceptibility of constant drug delivery to vertical displacement of syringe pumps and impairs the occlusion alarm function. Therefore, any air in syringe of infusion pump systems should be carefully removed. To avoid infusion boluses of short-acting vasoactive drugs after accidental occlusions, the occluded infusion line should be released to ambient pressure first.