Objectives: To evaluate reliability and feasibility of the respiratory variability of pulmonary velocity-time integral as a new dynamic marker of fluid responsiveness in mechanically ventilated patients.
Design: Prospective observational study.
Setting: Medical-surgical ICU of a general hospital.
Patients: Fifty mechanically ventilated patients with acute circulatory failure.
Interventions: Transthoracic echocardiography was performed at inclusion (transthoracic echocardiography baseline). Fluid therapy was prescribed to patients exhibiting one value greater than or equal to 13% among commonly used variables of fluid responsiveness: respiratory variability of aortic velocity-time integral, respiratory variability of inferior vena cava diameter, or pulse pressure variation.
Measurements and main results: Respiratory variability of pulmonary velocity-time integral was assessed at baseline. Respiratory variability of pulmonary velocity-time integral was significantly greater in patients who received fluid therapy (26.9 ± 12.5% vs 6.2 ± 4.3%; p < 0.0001). Respiratory variability of pulmonary velocity-time integral was correlated with respiratory variability of aortic velocity-time integral (r = 0.75; p < 0.0001), respiratory variability of inferior vena cava diameter (r = 0.42; p < 0.01), and pulse pressure variation (r = 0.87; p < 0.0001) at baseline and with the relative increase in cardiac output after fluid therapy (r = 0.44; p = 0.019). Fluid responsiveness was defined as a 10% increase in cardiac output after fluid therapy, assessed by a second transthoracic echocardiography. Respiratory variability of pulmonary velocity-time integral was associated with fluid responsiveness (adjusted odds ratio, 1.58; 95% CI, 1.08-2.32; p = 0.002). Area under the receiver operating characteristics curve was 0.972, and a value of respiratory variability of pulmonary velocity-time integral greater than or equal to 14% yielded a sensitivity of 92% and specificity of 87% to predict fluid responsiveness. Interobserver reproducibility was excellent (intraclass correlation coefficient = 0.94).
Conclusions: Respiratory variability of pulmonary velocity-time integral is a simple and reliable marker of fluid responsiveness for ventilated patients in ICU.