Single-cannula venovenous bypass for respiratory membrane lung support.

Clinical use of a single cannula would make extracorporeal membrane oxygenation simpler and less aggressive. It would probably limit the occurrence of the complications of currently used techniques (double-cannula, venoarterial, or venovenous bypass). In this experimental study an original system is described that is composed of a single cannula, an alternating clamp, and a nonocclusive roller pump, the characteristics of which permit its use as a venous reservoir. To overcome the limitations of the oxygenation in any venovenous bypass, we used the method of "apneic oxygenation" through the natural lungs, which we previously proved efficient in infants and children. The optimal setting of the alternative clamp was first tested in vitro to obtain the maximal flow in the circuit and the minimal amount of recirculation. The single-cannula bypass then was compared with a two-cannula circuit regarding the efficiency of carbon dioxide removal and the hemodynamic consequences. At less than 50% of the maximal speed of the pump, flows were equivalent in both types of circuits. The efficiency of carbon dioxide removal was only slightly decreased by the use of a single cannula (30 +/- 2 ml/min versus 36 +/- 2 ml/min with two cannulas). This could easily be offset by increasing the gas flow/blood flow ratio in the oxygenator. Arterial carbon dioxide tension was maintained at normal levels in both types of circuits. Hemodynamic condition was only slightly affected by the alternative flow of the bypass. This system of single-cannula membrane lung support thus seems to be adequate for clinical use.