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Hypothesis: Pulse pressure variation (PPV) and aortic blood velocity variation (ABV) both are used to predict fluid responsiveness in mechanically ventilated patients. However, ABV has been reported to be less influenced by vasopressor support than PPV.Objectives: is to compare the PPV to Aortic Blood Velocity variation (ABV) as a predictor of volume responsiveness in patients on mechanical ventilation receiving high dose vasopressor.Design: A prospective study.Setting: Medical and surgical intensive care unit at a private hospital.Patients: Twenty-nine mechanically ventilated patients hospitalized for >24 hrs receiving high dose vasopressor with a pulse pressure variation of < 12%. High dose vasoactive drugs was defined as (norepinephrine / epinephrine > 0.3 mcg/kg/min or dopamine >15mcg/kg/min).Interventions: Doppler echocardiography (including measurement of TAPSE,ABV, LVEF and stroke volume) was performed before and after infusion of 500 mL of crystalloid solution. Patients were classified into two groups according to their response to fluid infusion: responders (at least 15% increase in stroke volume) and nonresponders.Measurements and Main Results: Twelve patients (41%) were responders and 17 (59%) were nonresponders. Before volume expansion, PPV was statistically higher in the responder group (7.79 [1.72] vs 4.5 [2.72], p <0 .003). A PPV cutoff value of 6.8% discriminated between responders and nonresponders with a sensitivity of 58% and a specificity of 65%.The area under the curve of the receiver operating characteristic curve was 0.78 (95% confidence interval, 0.62 – 0.95). ABV was significantly higher in the responder group (10.4 [2.53] vs 5.38 [1.85], p <0 .0001). An ABV cutoff value of 7.9% discriminated between responders and nonresponders with a sensitivity of 92% and a specificity of 94%.The area under the curve of the receiver operating characteristic curve was 0.98 (95% confidence interval, 0.84 –0.99).Conclusions: Aortic blood velocity variation is less influenced by high dose vasopressor infusion and can discriminate better between responder and non responder than pulse pressure variation in hypotensive patients on mechanical ventilation receiving high dose vasopressor.