Objective: To determine the effect of syringe size on safety and reliability of low-flow infusions at rates relevant to hemodynamically unstable infants.
Design: In vitro study using readily available clinical equipment.
Setting: Medical–surgical pediatric intensive care unit of a university-affiliated hospital.
Interventions: Three-, 12-, and 60-mL syringes (Kendall Monoject) with extension tubing were mounted in identical Baxter AS50 infusion pumps. We determined time to alarm after occlusion of the distal tubing. We described and validated a method using capillary tubes to determine startup time to reach steady-state flow and variability of steady-state flow. Data were analyzed using single-factor analysis of variance or linear regression, as appropriate.
Measurements and Main Results: At 5 mL/hr flow, time to alarm occlusion (mean ± sd) was 1:08 ± 0:42, 3:35 ± 0:58, and 27:06 ± 3:26 minutes for 3-, 12-, and 60-mL syringes, respectively (p < .00001). At a lower flow of 0.2 mL/hr, none of the pumps alarmed despite 30 mins of distal occlusion, regardless of syringe size. Validation testing of the capillary tube volumetric method revealed a sd <5% of the average fluid column displacement. Startup time to reach steady-state flow of 0.2 mL/hr for 60-mL syringes was 76 ± 40 mins and significantly exceeded 24 ± 10 mins for 3-mL syringes (p = .041). In one test using a 60-mL syringe, flow remained below 20% of steady state for >3 hrs. Average steady-state flow was similar for the three syringe sizes (p = .2861), but sd of steady-state flow was directly related to syringe size and regressed to a line with r2 = 1.
Conclusions: Syringe size is related to time to reach steady-state flow, time to alarm occlusion, and variability of low-flow infusions.