Optimizing Pulsatility in Minimally Invasive Extracorporeal Circulation (MiECC)

Objectives: Pulsatile extracorporeal circulation (ECC) may improve organ perfusion in cardiac surgery. Some minimally invasive ECC (MiECC) systems provide optional pulsatile perfusion. Surplus hemodynamic energy (SHE) describes the gain in hemodynamic energy provided by pulsation over laminar flow. We investigated effects of oxygenators, arterial cannulae, and drive settings on SHE in a mock circulation.

Methods: The mock circulation contained a compliant aortic model with human geometry. Flows at the aortic arch, renal, and femoral branches were adjusted to physiologic values. A commercial MiECC system with a diagonal pump and an oxygenator perfused the aorta with a dextran solution. Hemodynamic parameters including SHE (as % of arterial pressure) were computed from flow and pressure data. Drive settings were varied individually starting at previously established clinical defaults.

Results: The choice of oxygenator had only a minor effect on SHE in spite of up to two-fold differences in pressure drops. Four models peaked at approx. 7.5% (2 L/min), one at 8.8% (8.6–9.2%) at 1.5 L/min. SHE did not exceed 4.6% (4.5–4.7%) at 3.5 L/min. Increasing rotational speed amplitude to 2,500 delta rpm shifted SHE to a maximum of 10.2% (10.1–10.4%) and to 5.2% (5.1–5.3%) at 2 L/min. Limiting pulse frequency to 40/min raised SHE to 16.0% (15.5–16.7%) at 1.5 L/min and to 5.5% (5.4–5.7%) at 3.5 L/min. Maximum SHE was 14.2% (13.9–14.7%) with a systolic fraction of 0.3 at 1.5 L/min but peaked at a fraction of 0.4 with higher flow rates, reaching no more than 4.0% (4.0–4.3%) at 3.5 L/min. All optimizations combined delivered a peak SHE of 22.5% (21.3–23.2%) at 1.0 L/min and a SHE of 5.2% (5.0–5.2%) at 3.5 L/min. Addition of a 15-Fr cannula abolished SHE at 3.5 L/min. A 23-Fr cannula limited SHE to 24.1% (23.9–25.2%) at 1 L/min and to 1.5% (1.4–1.7%) at 3.5 L/min. Addition of a second pump with synchronous pulsation shifted the SHE curve to the right, reaching 24.6% (24.4–25.5%) at 1 L/min and 5.0% (4.6–5.2%) at 3.5 L/min in the presence of the 23-Fr cannula.

Conclusion: Systematic optimization of MiECC in a mock circulation allowed to obtain peak SHE values higher than those resulting from empirical clinical defaults. However, peaks were observed at volumetric flow rates too low for adult ECC. Experimental dual-pump setups may satisfy the demand for acceptable SHE at flow rates adequate for adult ECC.