Continuous measurement of cardiac output by the Fick principle in infants and children: Comparison with the thermodilution method

Objective To compare a system that continuously monitors cardiac output by the Fick principle with measurements by the thermodilution technique in pediatric patients.Design Prospective direct comparison of the above two techniques.Setting Pediatric intensive care unit of a university hospital.Patients 25 infants and children, aged 1 week to 17 years (median 10 months), who had undergone open heart surgery were studied. Only patients without an endotracheal tube leak and without a residual shunt were included.Methods The system based on the Fick principle uses measurements of oxygen consumption taken by a metabolic monitor and of arterial and mixed venous oxygen saturation taken by pulse- and fiberoptic oximetry to calculate cardiac output every 20 s.Interventions In every patient one pair of measurements was taken. Continuous Fick and thermodilution cardiac output measurements were performed simultaneously, with the examiners remaining ignorant of the results of the other method.Results Cardiac output measurements ranged from 0.21 to 4.55 l/min. A good correlation coefficient was found:r²=0.98;P<0.001; SEE=0.14 l/min. The bias is absolute values and in percent of average cardiac output was –0.05 l/min or –4.4% with a precision of 0.32 l/ min or 21.3% at 2 SD, respectively. The difference was most marked in a neonate with low cardiac output.Conclusion Continuous measurement of cardiac output by the Fick principle offers a convenient method for the hemodynamic monitoring of unstable infants and children.