Determination of cardiac output by ultrasound dilution technique in infants and children: a validation study against direct Fick principle.

Abstract

In critically ill children, monitoring of cardiac output (CO) is essential to guide haemodynamic management and facilitate cardiovascular therapy. The ultrasound dilution technique (UDT), a novel minimally invasive indicator method, was recently introduced to determine CO. We validated UDT against the 'gold standard' reference technique, the direct Fick principle, in infants and children. Twenty-six children (median age: 6 yr 2 months; median weight: 19.2 kg) underwent diagnostic heart catheterization. In each child, CO was determined by the Fick principle using direct measurement of oxygen consumption and invasive oximetry. Consecutively, haemodynamically stable conditions provided; three independent measurements of CO were conducted with UDT. CO values were compared using bias and limits of agreement calculated using the Bland-Altman approach and linear regression analysis for the complete study group and for a subgroup with body weight <20 kg (n=14). The mean (standard deviation) CO values were 3.76 (1.73) litre min(-1) (range 1.38-6.97) for the direct Fick principle and 3.49 (1.72) litre min(-1) (range 1.31-7.00) for UDT. An excellent correlation (r=0.96) was found between both methods (P<0.0001). The Bland-Altman analysis demonstrated good clinical agreement with a mean bias of 0.26 litre min(-1), limits of agreement of -0.66 and 1.19 litre min(-1), and percentage error of 25.9%. Comparable results were obtained for patients <20 kg (mean bias=0.19 litre min(-1), percentage error=25.5%). CO measurements by UDT agree favourably with Fick-derived CO data and both techniques were found to be equivalent and interchangeable. UDT represents a valid and applicable method for repetitive CO determinations in infants and children.