Development of an artificial placenta: CO2 elimination and hemodynamics as a function of arteriovenous blood flow

As a first step toward the development of an artificial placenta, we investigated the relationship between blood flow rate through an arteriovenous (A-V) circuit/oxygenator and both CO2 elimination and hemodynamic stability in a small animal model.

Male New Zealand rabbits (N = 10) with an average weight of 2.7 +/- 0.2 kg were anesthetized, paralyzed, and heparinized before carotid-jugular cannulation. A tracheostomy tube, an arterial catheter, and an aortic flow probe were placed. Arteriovenous flow through a custom-made, low-resistance, 0.5 m2 hollow fiber oxygenator was initiated. Oxygen sweep flow was maintained at 300 mL/min, whereas blood flow was controlled at 10 to 40 mL/(kg min). Ventilation was discontinued during each blood flow rate trial. Hemodynamic and preoxygenator and postoxygenator blood gas data were recorded 30 minutes after initiation of each flow rate. CO2 removal was the product of the oxygen sweep gas flow rate and the sweep flow exhaust CO2 content as determined by capnometry. Data were analyzed by analysis of variance with post hoc Dunnett's t test.

CO2 removal increased and PaCO2 decreased as a function of A-V blood flow rate. Simultaneously, systolic blood pressure did not significantly change. CO2 removal was effective at device flows greater than 20% of cardiac output.

In this rabbit model, A-V blood flows at 25% to 30% of cardiac output allow full gas exchange without hemodynamic compromise. This model raises the possibility of using A-V support and an artificial placenta in newborns with respiratory failure.