Measurement of cardiac output with a non-invasive continuous wave Doppler device versus the pulmonary artery catheter: a comparative study.

INTRODUCTION AND AIM: Cardiac index remains an important measured variable used to optimise fluid and haemodynamic support in the postoperative cardiac setting. Recent developments in non-invasive continuous wave Doppler devices enable rapid assessment of cardiac index with decreased morbidity. This study aimed to determine the clinical utility of one such device, the USCOM device (USCOM Ltd, Sydney, NSW), in assessing cardiac index compared with invasive continuous measurements of cardiac index using a pulmonary artery (PA) catheter.

METHODS: A prospective study was undertaken in patients admitted to an intensive care unit after cardiac revascularisation, open-heart surgery or cardiac or pulmonary transplant, most of whom required haemodynamic support. Cardiac index was measured by a single operator using the USCOM device. Continuous cardiac index measurements using the PA catheter were obtained (blinded to USCOM measurements) within 15 minutes of the USCOM measurement.

RESULTS: 30 patients were enrolled. Adequate Doppler signals were obtained in 26, yielding 34 paired measurements. Comparison of the two methods using a Bland-Altman analysis identified a bias of 0.22 with limits of agreement of - 1.17 (- 1.53 to - 0.82) and 1.62 (1.26 to 1.97), representing limits of agreement for interchangeability of 52%.

CONCLUSION: In a heterogeneous population of postoperative cardiac patients, non-invasive determination of cardiac index using USCOM had limited clinical utility. Doppler flow signal quality may have been affected by intrathoracic air, patient position and operator learning curve. Given accepted inherent inaccuracies of continuous cardiac output assessment, further investigation is required to validate the suitability of USCOM in this patient population.