The effects of syringe plunger design on drug delivery during vertical displacement of syringe pumps

Fluid delivery from four types of commercially available 50-ml syringes was measured using an electronic balance at an infusion rate of 1 ml.h(-1). Re trograde aspiration volume and zero-drug delivery time were recorded after lowering the syringe pump by 50 cm. Syringe compliance was calculated from the volume of bolus released after occlusion at 100 mmHg. Zero-drug deliver y times differed significantly between syringes, ranging from [mean (SD)] 3 .26 (0.40) min to 6.38 (0.56) min (F = 55.5, d.f. = 3/20, p < 0.0001). Syri nge compliance correlated well with aspiration volume (Pearson r(2) = 0.92, p < 0.001) and zero-drug delivery time (r(2) = 0.90, p < 0.001). Syringe d esign affected the internal syringe compliance. All syringes were associate d with potentially relevant zero-drug delivery times after moderate vertica l displacement. To minimise this risk, vertical displacement of syringe pum ps delivering highly vasoactive drugs should be avoided.