Training is required to improve the reliability of esophageal Doppler to measure cardiac output in critically ill patients

Objectives: Assessment of and effect of training on reliability of esophageal Doppler (ED) versus thermodilution (TD) for cardiac output (CO) measurement. Design: Prospective study. Setting: Intensive care unit of a university hospital. Patients: 64 consecutive critically ill patients requiring a pulmonary artery catheter, sedation, and mechanical ventilation. Interventions: Esophageal Doppler CO measurements were performed by the same operator, whereas TD CO measurements were carried out by other independent operators. A training period involving the first 12 patients made the operator self-confident. In the remaining patients, the reliability of ED was assessed (evaluation period), using correlation coefficients and the Bland and Altman diagram. Between training and evaluation periods, correlation coefficients, biases, and limits of agreement were compared. Measurements and results: During training and evaluation periods, 107 and 320 CO measurements were performed in 11 out of 12 patients and in 49 out of 52 patients, respectively. Continuous CO monitoring was achieved in 6 out of 11 patients and in 38 out of 49 patients during training and evaluation periods, respectively. Between the two periods, correlation coefficients increased from 0.53 to 0.89 (p < 0.001), bias decreased from 1.2 to 0.1 l.min(-1) (p < 0.001), and limits of agreement decreased from 3.2 to 2.2 l.min(-1) (p < 0.001). Conclusion: A period of training involving no more than 12 patients is probably required to ensure reliability of CO measurement by ED.