We employ veno-venous extracorporeal membrane oxygenation (V-V ECMO) to address severe respiratory failure. In V-V ECMO, a variable proportion of oxygenated blood from the return cannula enters the drainage cannula. This condition is known as recirculation. Increased recirculation rates may result in insufficient blood oxygenation. Cannula design may influence recirculation rates. Therefore, in this study, I investigated the effects of the length of the side hole portion and the intervals of the side holes in drainage cannulae on the recirculation rate and blood oxygenation.
As shown in Figure 1, I manufactured drainage cannulae with side holes, respectively. I inserted drainage and return cannulae into the simulated circuit, positioning the tip of the drainage cannula in the atrium and the return cannula in the superior vena cava. I filled the simulated circuit, including the venous reservoir, with 5 L of porcine blood. Prior to initiating ECMO, I adjusted the blood oxygen saturation to 60 ± 5% and the partial pressure of carbon dioxide to 70 ± 10 mmHg. After initiating ECMO, I measured the recirculation rate and the arterial oxygen pressure (PaO2).
The recirculation rate and PaO2 were as follows: (a) 5 cm: 54 ± 5 % and 95 ± 7 mmHg; (b) 10 cm: 38 ± 1 % and 139 ± 8 mmHg; (c) 15 cm: 31 ± 1 % and 166 ± 6 mmHg; (d) 3 cm intervals: 34 ± 1 % and 154 ± 7 mmHg; (e) 5 cm intervals: 39 ± 1 % and 134 ± 7 mmHg, respectively (n = 6).
In V-V ECMO, we should use cannulae with long side hole portions.
