A Comparison of Static Occlusion Setting Methods : Fluid Drop Rate and Pressure Drop

Tubing circuits primed with water were constructed on two roller pumps to characterize and compare two static methods of setting the occlusion on roller pumps (fluid drop rate and pressure drop rate). Twelve separate experiments were performed in which PVC boot tubing diameters (1/2 in, 3/8 in and 1/4 in), roller position (each roller alone on a two roller pump) and roller occlusion (total occlusion to 0.004 in underocclusion) were varied. Fluid drop rates were measured from two heights (30 in and 1 m) above the pump head where drops of 1 em and 1 in were timed for each occlusion setting. Pressure drop was measured by clamping the outlet tubing, injecting fluid into the tubing between the clamp and roller elevating the pressure to 300 mmHg and observing the rate that it dropped at each occlusion setting. Fluid drop rate and pressure drop rate were positively correlated at all occlusion settings and tubing sizes (p < 0.001). Using a single roller occlusion and an optimal fluid drop rate of .5 to 1.5 em/min. at 30 in height, pressure drops (mmHg/min.) were (mean± SD); 1/2 in tubing= 263 ± 33, 3/8 in= 241 ±52, 1/4 in= 264 ± 11. For a fluid drop rate of 1.27 to 3.81 em/min. at 1 m height, pressure drops were (mean± SD); 1/2 in= 266 ± 33, 3/8 in=278 ± 17, 114 in=274 ± 20. The occlusion settings or occlusion gap varied significantly (p < 0.001) between pumps and tubing sets. Thus, it appears as though pressure drop rate can predict fluid drop rate at just nonocclusive pump settings; however, the occlusion should be rechecked every time a different pump or boot tubing is used. Volume 28, Number 1, March 1996 Address correspondence to : Thomas Rath, BS c/o Robin Sutton, MS, CCP Department of Surgery 1601 JCP University of Iowa Hospitals and Clinics Iowa City, lA 52242