title: Syringe size and flow rate affect drug delivery from syringe pumps.
abstract: OBJECTIVE
  To evaluate the effect of syringe size and infusion rate on drug delivery after vertical displacement of syringe pumps.
  
  
  METHODS
  Four syringes (10 ml, 20 ml, 30 ml, 50 ml) were studied at three infusion speeds (2 ml x hr(-1), 1 ml x hr(-1) and 0.5 ml x hr(-1)). Fluid delivery was measured gravimetrically using an electronic balance. Aspiration volume (amount of fluid retracted into the syringe-infusion line assembly) and zero-drug delivery time (time between the lowering of the syringe pump and reattainment of the initial weight) were determined after lowering the syringe pump 130 cm or 50 cm. Then, infusion bolus was measured after elevating the pump to its initial position. Syringe compliance was calculated from the occlusion release bolus at an occlusion pressure of 300 mmHg.
  
  
  RESULTS
  Zero-drug delivery time, aspiration volume and infusion bolus increased with syringe size (P < 0.0001). At 0.5 ml x hr(-1), a zero-drug delivery time of 29.7 +/- 0.6 min was recorded for the 50 ml syringe and 5.5 +/- 0.15 min for the 10 ml syringe. As infusion rates increased, zero-drug delivery times decreased following a 1/x ratio. Zero-drug delivery time highly correlated with calculated syringe compliance (Pearson's r = 0.97, P < 0.001), which was closely related to syringe plunger area (R2 = 0.93, P < 0.001).
  
  
  CONCLUSIONS
  Vertical displacement of syringe pumps causes flow irregularities which correlate directly with syringe size and indirectly with infusion rate. Extreme vertical maneuvering of syringe pumps should be avoided. Infusion rates > or = 1 ml x hr(-1) and low-compliant, small syringes are recommended when highly concentrated drugs are administered.
authors.affiliation: Department of Anaesthesia, University Children's Hospital, Zurich, Switzerland. markus.weiss@kispi.unizh.ch
authors.forename: M
authors.initials: M
authors.lastname: Weiss
authors.forename: M I
authors.initials: MI
authors.lastname: Hug
authors.forename: T
authors.initials: T
authors.lastname: Neff
authors.forename: J
authors.initials: J
authors.lastname: Fischer
mesh_terms: D006801:Humans; D007260:Infusion Pumps; D013594:Syringes