Use of transesophageal Doppler ultrasonography in ventilated pediatric patients: Derivation of cardiac output

Objective: To ascertain if cardiac output (CO) could be derived from blood flow velocity measured in the descending aorta of ventilated children by transesophageal Doppler ultrasonography (TED) without the need for direct aortic cross sectional area measurement, and to evaluate the ability of TED to follow changes in CO when compared with femoral artery thermodilution. Design: Prospective, comparison study. Setting: A 16-bed pediatric intensive care unit of a university hospital. Patients: A total of 100 ventilated infants and children aged 4 days to 18 yrs (median age, 27 months). Diagnoses included postcardiac surgery (n = 58), sepsis/multiple organ failure (0 = 32), respiratory disease (n = 5), and other (n = 5). A total of 55 patients were receiving inotropes or vasodilators. Interventions: When patients were hemodynamically stable, a TED probe was placed into the distal esophagus to obtain optimal signal, and minute distance (MD) was recorded. Five consecutive MD measurements were made concurrently with five femoral artery thermodilution measurements, and the concurrent measurements were averaged. CO was then manipulated by fluid administration or inotrope adjustment, and the readings were repeated. Measurements and Main Results: Femoral artery thermodilution CO ranged from 0.32 to 9.19 L/min, (median, 2.46 L/min), and encompassed a wide range of high and low flow states. Theoretical consideration revealed the optimal TED estimate for CO to be (MD x patient height(2) x 10(-7)). Linear regression analysis yielded a power function model such that: estimated CO = 1.158 x (MD x height(2) x 10(-7))(0.785), r(2) = 0.879, standard error of the estimate = 0.266. Inclusion of a correction factor for potential changes in aortic cross-sectional area with hypo- and hypertension did not appreciably improve the predictive value of the model. MD was able to follow percentage changes in CO, giving a mean bias of 0.87% (95% confidence interval -0.85% to 2.59%), and limits of agreement of +/- 16.82%. The median coefficient of variation for MD was 3.3% Conclusions: TED provides a clinically accurate estimate of CO across the entire pediatric age range and is able to follow changes in CO.