The Effect of Syringe Pump Vertical Position and Residual Air on the Stability of Vasoactive Drug Infusion: A...

Hemodynamic instability during vasoactive drug infusion remains a clinical challenge. While macroscopic factors are well-studied, the physical interaction between syringe residual air and vertical pump positioning is often overlooked. This study investigates how these factors synergistically disrupt flow stability using a simplified simulation model.

A simulation model was constructed using a 60 mL syringe, infusion tubing, and two 3-way stopcocks. The system was tested under four conditions: with or without 1 mL of air in the syringe, and with the infusion terminal positioned 25 cm or 50 cm below the syringe level. Droplet formation at the terminal stopcock was quantified over 10 s intervals using a standardized visual scale. Each condition was repeated 30 times (n = 120 trials). Data were analyzed using non-parametric tests.

The presence of 1 mL of air significantly increased flow instability, yielding higher droplet counts compared to the no-air group at both 25 cm (median: 0.75 vs. 0.25 drops, p < 0.001) and 50 cm (median: 2.25 vs. 0.75 drops, p < 0.001). Increasing the height from 25 cm to 50 cm also significantly raised droplet output: from 0.25 to 0.75 drops without air (p < 0.001), and from 0.75 to 2.50 drops with 1 mL of air (p < 0.001). The greatest instability occurred under the combined condition of 50 cm height with 1 mL of air.

Residual syringe air and infusion pump vertical position are critical, interacting factors that disrupt flow continuity during vasoactive drug delivery. Air bubbles induce transient flow variations, while height differences amplify these effects through hydrostatic pressure. Clinical protocols should emphasize meticulous air elimination and consistent pump positioning at the level of the patient's right atrium to minimize avoidable infusion-related hemodynamic instability.