Cannulation configuration and recirculation in venovenous extracorporeal membrane oxygenation

Abstract

Venovenous extracorporeal membrane oxygenation is a treatment for acute respiratory distress syndrome. Femoro-atrial cannulation means blood is drained from the inferior vena cava and returned to the superior vena cava; the opposite is termed atrio-femoral. Clinical data comparing these two methods is scarce and conflicting. Using computational fluid dynamics, we aim to compare atrio-femoral and femoro-atrial cannulation to assess the impact on recirculation fraction, under ideal conditions and several clinical scenarios. Using a patient-averaged model of the venae cavae and right atrium, commercially-available cannulae were positioned in each configuration. Additionally, occlusion of the femoro-atrial drainage cannula side-holes with/without reduced inferior vena cava inflow (0-75%) and retraction of the atrio-femoral drainage cannula were modelled. Large-eddy simulations were run for 2-6L/min circuit flow, obtaining time-averaged flow data. The model showed good agreement with clinical atrio-femoral recirculation data. Under ideal conditions, atrio-femoral yielded 13.5% higher recirculation than femoro-atrial across all circuit flow rates. Atrio-femoral right atrium flow patterns resembled normal physiology with a single large vortex. Femoro-atrial cannulation resulted in multiple vortices and increased turbulent kinetic energy at > 3L/min circuit flow. Occluding femoro-atrial drainage cannula side-holes and reducing inferior vena cava inflow increased mean recirculation by 11% and 32%, respectively. Retracting the atrio-femoral drainage cannula did not affect recirculation. These results suggest that, depending on drainage issues, either atrio-femoral or femoro-atrial cannulation may be preferrable. Rather than cannula tip proximity, the supply of available venous blood at the drainage site appears to be the strongest factor affecting recirculation.

Figure 1

CT images showing the two separate acquisitions used to create a full reconstruction of the venae cavae and right atrium (left). The atrio-femoral and femoro-atrial cannulation models (right).

Figure 2

(A) Recirculation fraction ($R_f)$ under atrio-femoral and femoro-atrial cannulation compared to results from Palmér et al. for a range of venovenous extracorporeal membrane oxygenation (VV ECMO) flow rates. SVC = superior vena cava, IVC = inferior vena cava, TV = tricuspid valve, CS = coronary sinus. (B) Time-averaged velocity streamlines for both cannula configurations at 6L/min and the right atrium (RA) with no cannulae. (C) Volume-averaged turbulent kinetic energy (TKE) in the RA for a range of VV ECMO flow rates ($Q_{\mathit{ec}})$. The grey dotted line represents volume-averaged RA TKE in a model without any cannulae. (D) A volume representation of TKE for both cannula configurations at 6 L/min and the RA with no cannulae.

Figure 3

(A) Recirculation fraction ($R_f)$ under femoro-atrial venovenous extracorporeal membrane oxygenation (VV ECMO) with occluded and patent side-holes in the drainage cannula and for a range of decreased inferior vena cava (IVC) inflows (75–0%, 2.9–0 L/min). Occ. = occluded side-holes, SVC = superior vena cava. (B) $R_f$ under atrio-femoral VV ECMO for three drainage cannula positions: baseline at junction of SVC and right atrium, mid SVC and distal SVC.

Figure 4

Effective extracorporeal membrane oxygenation (ECMO) flow rate ($Q_{\mathit{eff}})$ versus ECMO flow rate ($Q_{\mathit{ec}})$ for the atrio-femoral and femoro-atrial cannulation configurations. $Q_{\mathit{eff}}$ obtained from the femoro-atrial model with occluded drainage cannula side-holes and reduced inferior vena cava (IVC) inflow are also plotted. Occ. = occluded side-holes. In pink we show a schematic curve of the expected relationship between $Q_{\mathit{eff}}$ and $Q_{\mathit{ec}}$ (circuit blood flow) proposed by Abrams et al..