Clinical validation of cardiac output measurements using femoral artery thermodilution with direct Fick in ventilated children and infants.

Objective: To validate clinically cardiac output (CO) measurements using femoral artery thermodilution in ventilated children and infants by comparison with CO estimated from the Fick equation via a metabolic monitor. Design: Prospective, comparison study. Setting: Paediatric intensive care unit of a university hospital. Patients: 24 ventilated infants and children, aged 0.3 to 175 months (median age 19 months). Interventions: Oxygen consumption measurements were made and averaged over a 5-min period, at the end of which arterial and mixed venous blood samples were taken and oxygen saturations measured by co-oximetry, with CO being calculated using the Fick equation. Over this 5-min period, five sets of femoral arterial thermodilution (FATD) measurements were made and averaged. One comparison of CO values was made per patient. Results: Mean Fick CO was 2.55 l/min (range 0.24 to 8.71 l/min) and mean FATD CO was 2.51 l/min (range 0.28–7.96 l/min). The mean bias was 0.03 l/min (95 % confidence interval –0.07 to 0.14 l/min), with limits of agreement of –0.45 to 0.52 l/min. When indexed to body surface area, the mean Fick cardiac index became 3.51 l/min per m2 (1.52–6.98 l/min per m2) and mean FATD 3.49 l/min per m2 (1.74–6.84 l/min per m2). The mean bias was 0.02 l/min per m2 (95 % confidence interval –0.11 to 0.15 l/min per m2) with limits of agreement of –0.57 to 0.61 l/min per m2. The mean FATD coefficient of variation was 5.8 % (SEM 0.5 %). Conclusions: FATD compares favourably with Fick derived CO estimates in infants and children and may represent an advance in haemodynamic monitoring of critically ill children.