Cardiopulmonary bypass surgical techniques that allow a surgeon to operate on the infant's heart use an extracorporeal circuit consisting of a pump, oxygenator, arterial and venous reservoirs, cannulae, an arterial filter, and tubing. The extracorporeal technique currently used in infants and neonates is sometimes associated with neurologic damage. We are developing a modified cardiopulmonary bypass system for neonates that has been tested in vitro and in one animal in vivo. Unlike other extracorporeal circuits which use steady flow, this system utilizes pulsatile flow, a low prime volume (500 ml) and a closed circuit. During in vitro experiments, the pseudo patient's mean arterial pressure was kept constant at 40 mmHg and the extracorporeal circuit pressure did not exceed a mean pressure of 200 mmHg. In our single in vivo experiment, the primary objective was to determine whether physiologic pulsatility with a 10 F (3.3 mm) aortic cannula could be achieved. The results suggest that this is possible.
Neurologic complications are already well documented after cardiopulmonary bypass (CPB) procedures in neonates and infants. Physiologic pulsatile flow CPB systems may be the alternative to the currently used steady-flow CPB circuits. In addition to the pulsatile pump, a membrane oxygenator should be chosen carefully, because only a few membrane oxygenators are suitable for physiologic pulsatile flow. We have tested four different types of neonate-infant membrane oxygenators for physiologic pulsatility with The University of Texas neonate-infant pulsatile CPB system in vitro. Evaluation criteria were based on mean ejection time, extracorporeal circuit (ECC) pressure, and upstroke of dp/dt. The results suggested that the Capiox 308 hollow-fibre membrane oxygenator produced the best physiologic pulsatile waveform according to the ejection time, ECC pressure, and the upstroke of dp/dt. The Minimax Plus and Masterflo Infant hollow-fibre membrane oxygenators also produced adequate pulsatile flow. Only the Variable Prime Cobe Membrane Lung (VPCML) Plus flat-sheet membrane oxygenator failed to reach the criteria for physiologic pulsatility. Depending on the oxygenator used, the lowest priming volume of the infant CPB circuit was 415 ml and the highest 520 ml.
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