Reduction of Restoring Force of Tubing through Prolonged Use in Cardiopulmonary Bypass Machines Leads to Decrease of Effective Output

Objectives: Cardiopulmonary bypass (CBP) machines use roller pumps to ensure a continuous blood flow through their tubing. It is tempting to see the movement of these pumps as only factor regulating the blood output without taking into account the role of the restoring force of the tubing. As discussed in a recent paper regarding the position of the roller pump, factors like the negative pressures can hinder the compressed tubing segments from fully expanding before recompression thus measurably reducing the pumps output. One of these factors it the ageing of the tubing material following the prolonged compression during priming and use of the CBP. Here, we report on our findings regarding reset force and effective roller pump output of silicone tubing after prolonged use.

Methods: CBP tubing was tested fresh, after 4 and 8 hours of compression in a roller tube. To measure the restoring force, the tubing segments clamped inside the pump (length: ~22 cm, volume ~ 27 mL) were separated and sealed on both sides. Afterward the force necessary to extract 18 mL (66.7% of the volume) was measured and compared. To test the influence on the effective performance of the roller pump, the tubing was installed in a separate pumping system and the effective output at target flows of 3, 4.5, and 6 L/min were measured after 0, 4, and 8 hours, respectively.

Results: Restoring force per cm tubing was significantly (p < 0.001) reduced after prolonged compression in the roller pump (0.374 ± 0.031 N/cm) compared to fresh tubing (0.619 ± 0.020 N/cm), corresponding to a 40% decrease. This resulted in a measurable decrease in effective pump performance at all three target flows (means and 95% confidence intervals: 3 L/min: −1.76 [1.27–2.24]%, 4.5 L/min: −1.59 [0.95–2.23]%, 6 L/min: −1.89 [1.37–2.42]%).

Conclusions: The ageing of the CBP tubing material in response to the ongoing compression within the roller pump leads to a detectable reduction of the pumps performance. This can and should be considered especially during CBP over prolonged time periods or after extensive priming by introducing a corresponding correction factor.

Keywords CBP; roller pumps; performance; tubing