Measurement of cardiac output in infants less than 10 kg: accuracy of femoral artery thermodilution as compared to direct Fick

Introduction

Femoral artery thermodilution (FATD) has proven a useful technique for the measurement of cardiac output (CO) in children as it avoids the problems associated with pulmonary artery catheterisarion by placing the thermistor in the femoral artery. We wished to evaluate the accuracy of FATD using a commercially available device (COLD Z-021, Pulsion, Munich) amongst infants less than 10 kg.

Methods

20 ventilated infants were studied following cardiac surgery, median weight 4.7 kg (range 2.5–10 kg). Absence of anatomical shunt was confirmed with Doppler Echocardiography. When haemodynamically stable, a 1.3 Fr thermistor was placed into the femoral artery via a percutaneously placed 22 gauge cannula. Five consecutive FATD measurements were made using iced 5% Dextrose solution (1.5 ml + 0.15 ml/kg body weight) given via a central venous cannula, then averaged. Over the same time period CO was also measured utilising the Fick principle, with O₂ consumption measured by a metabolic monitor (Deltatrac, Datex, Helsinki). Cuffed endotracheal tubes were used if air leaks of >5% of inspiratory tidal volume were present. Arterial and mixed venous O₂ contents were calculated using co-oximetry.

Results

There were no line related complications. Mean Fick CO was 0.77 l/min (range 0.32 to 2.21) mean FATD CO was 0.76 l/min (range 0.28 to 2.05). The mean bias was 0.009 l/min (95% confidence interval -0.03 to 0.05) with limits of agreement (mean bias ± 1.96 sd) of -0.15 to 0.17 l/min. The mean FATD coefficient of variation was 5.6%.

Conclusions

FATD is a safe, reproducible, clinically acceptable technique for bedside CO measurement in ventilated infants.