Introduction Cardiac output (CO) is an important indicator of overall cardiac function and intravascular volume status. Present methods of assessing CO at the bedside in older children and adults are invasive and technically unfeasible in the neonate. In recent years, a novel method of measuring cardiac output using a lithium dilution technique and existing vascular access has been developed. The LiDCO/PulseCO system (LiDCO Ltd, Cambridge, UK) of cardiac output monitoring uses an arterial pressure waveform to measure CO on a continuous basis after lithium dilution calibration (LDC).
Objective To assess (1) the feasibility of performing LDC using the LiDCO system and (2) the clinical utility of this system and its associated PulseCO software in measuring continuous CO compared to pulsed Doppler echocardiography (PDE) in an extremely preterm animal model.
Methods This study used a model of premature infant chronic lung disease as simulated at the SFBR in a 125-day gestation (approximate 25-week human equivalent) baboon model. A total of 10 animals were studied. Each animal had an existing umbilical artery catheter that was connected to the LiDCO system. Initial CO measured using PDE was recorded on all study animals within the first 24 hours of life. Each animal subsequently had an attempt made at LDC according to an established protocol. For those animals in which LDC was unsuccessful, calibration was performed using echocardiography, and CO measurements were serially collected over time and compared to those values obtained using standard PDE.
Results LDC/PDE value pairs were successfully obtained in 5 animals. From those animals, 40 PDE/PulseCOvalue pairs were also obtained. There was poor agreement between LDC/PDE pairs and PDE/PulseCOpairs. Lack of agreement between measurements seemed secondary to factors including recirculation of lithium indicator solution from patent ductus arteriosus, variations in flow properties of individual arterial catheters, and variations in the degree of illness of animals.
Conclusions Use of LDC and the LiDCO system including continuous cardiac output monitoring is feasible in a premature neonate model. The system was not clinically useful because of a lack of agreement between LDC and PDE measurements, but this may be due to technical factors that can be overcome with more experience. This system may still be a useful tool in neonates if a lack of significant drift over time can be demonstrated after calibration with PDE.
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