Respiratory changes in aortic blood velocity as an indicator of fluid responsiveness in ventilated patients with septic shock.

STUDY OBJECTIVE: To investigate whether the respiratory changes in peak velocity (Vpeak) of aortic blood flow could be related to the effects of volume expansion on cardiac index.

DESIGN: Prospective clinical study.

SETTING: Medical ICUs of a university hospital (20 beds) and of a nonuniversity hospital (15 beds).

PATIENTS: Nineteen sedated septic shock patients who were receiving mechanical ventilation and who had preserved left ventricular (LV) systolic function.

INTERVENTION: Volume expansion.

MEASUREMENTS AND RESULTS: Analysis of aortic blood flow by transesophageal echocardiography allowed beat-to-beat measurement of Vpeak before and after volume expansion. Maximum values of Vpeak (Vpeakmax) and minimum values of Vpeak (Vpeakmin) were determined over one respiratory cycle. The respiratory changes in Vpeak (Delta Vpeak) were calculated as the difference between Vpeakmax and Vpeakmin divided by the mean of the two values and were expressed as a percentage. The indexed LV end-diastolic area (EDAI) and cardiac index were obtained at the end of the expiratory period. The volume expansion-induced increase in cardiac index was > or = 15% in 10 patients (responders) and < 15% in 9 patients (nonresponders). Before volume expansion, Delta Vpeak was higher in responders than in nonresponders (20 +/- 6% vs 10 +/- 3%; p < 0.01), while EDAI was not significantly different between the two groups (9.7 +/- 3.7 vs 9.7 +/- 2.4 cm(2)/m(2)). Before volume expansion, a Delta Vpeak threshold value of 12% allowed discrimination between responders and nonresponders with a sensitivity of 100% and a specificity of 89%. Volume expansion-induced changes in cardiac index closely correlated with the Delta Vpeak before volume expansion (r(2) = 0.83; p < 0.001).

CONCLUSION: Analysis of respiratory changes in aortic blood velocity is an accurate method for predicting the hemodynamic effects of volume expansion in septic shock patients receiving mechanical ventilation who have preserved LV systolic function.