Purpose: To examine the delivery rates of four disposable, non-electric infusion pumps during hypobaric conditions.
Methods: Four models categorized by three different driving forces, one vacuum unit (Coopdech Syringector), one spring unit (Linear-fuser), and two elastomeric balloon-powered units (Multirate Infuser LV and Large DIB), were tested. Each infusion pump was placed in an airtight container, and the pressure in the container was decreased to 1,000, 900, and 800 hPa. The catheter tip of each pump was exposed either to atmospheric pressure (1,000 hPa) or to similar hypobaric conditions (800-1,000 hPa).
Results: Under normal atmospheric pressure, each pump showed an accurate delivery rate in the range of -2% to +8% of the set infusion rate (4.0-5.0 mL x hr(-1)). With the catheter tip exposed to atmospheric pressure, the infusion rate of each pump was reduced from 35% in the case of the Large DIB to 64% in the case of the Coopdech Syringector, depending on the magnitude of change in hypobaric pressure. When the pressure acting on the catheter tip was reduced to a level similar to that exerted on the pump body, infusion rate was reduced (by 19%-27%) in all three types of pump, and the Large DIB showed no significant difference in performance compared to normal atmospheric pressure.
Conclusion: The infusion rates of disposable infusion pumps are reduced under hypobaric conditions. Even though we still do not know how the epidural pressure changes under hypobaric conditions, clinicians should be aware that the infusion rate of disposable infusion pumps is decreased under hypobaric conditions.