Cardiac output measurement with transpulmonary ultrasound dilution is feasible in the presence of a left-to-right shunt: a validation study in lambs.

BACKGROUND Cardiac output (CO) monitoring remains complex in newborns as most of the current technologies fail to accurately measure systemic blood flow in the presence of shunts. We validated CO measurements using transpulmonary ultrasound dilution (TPUD) in a neonatal lamb model with a left-to-right shunt. METHODS Regular arterial and central venous catheters were inserted into seven lambs (3.5-8.3 kg). A surgically constructed left-to-right aorto-pulmonary Gore-Tex(®) shunt was intermittently opened and closed, while CO was manipulated by creating haemorrhagic hypotension. CO measurements with TPUD (COtpud) were compared with those obtained by an ultrasonic transit-time flow probe positioned around the main pulmonary artery (COufp). RESULTS We performed 72 sessions of three paired CO measurements. The mean COufp was 1.00 litre min(-1) (range 0.47-1.75 litre min(-1)) and mean COtpud 1.05 litre min(-1) (range 0.54-1.87 litre min(-1)). With an open shunt, the mean Qp/Qs ratio was 1.8 (range 1.3-2.6). A comparison between COufp and COtpud showed a mean bias (sd) of 0.03 (0.09) and 0.07 (0.10) litre min(-1), respectively, for measurements with a closed and an open shunt. The percentage error was 18% and 20% for measurements with a closed and an open shunt. Polar plot analysis showed good trending ability for both closed and open shunt groups. CONCLUSIONS TPUD is a reliable technology to measure CO in the presence of a left-to-right shunt.