Continuous monitoring of cardiac output in neonates using an intra-aortic Doppler probe

Continuous monitoring of cardiac output in neonates would be of considerable benefit but, as yet, there is no practical method to achieve this aim. We have now evaluated the feasibility of using an intraaortic Doppler probe. We introduced a pulsed Doppler probe of 0.46 mm diameter via the umbilical artery in two term and four preterm neonates. Indications in all patients for umbilical arterial catheter is always an unstable cardiopulmonary state. Body weights were between 770 and 3340 g. Velocities of blood flow in the thoracic aorta were continuously recorded to estimate cardiac output on-line for 12 h. No complications were encountered. It proved possible to derive high-quality Doppler curves. The received Doppler signal was stable but it proved sensitive to pathophysiologic changes in flow. Mean velocity of flow in the descending aorta was 16.4 cm/s (range 13-3-19.0 cm/s). We quantified flow by multiplying the mean velocity of the flow by the cross-sectional area of the descending aorta. Calculated mean flow was 135 ml/kg/mm (range 111-179 ml/kg/mm). These values are consistent with those measured by transcutaneous Doppler, and it should not be raised by left-to-right ductal shunts. This pilot study proved the feasibility of continuous monitoring of cardiac output. The technique should prove of great value in those infants with unstable circulatory conditions, and can be used even in infants with extremely low birth weights.