The perioperative hemodynamic management aims to ensure organ perfusion pressure and an oxygen arterial transport adapted to oxygen consumption. Phenylephrine is the α-adrenergic agonist widely used during anesthesia for arterial pressure control.

Several questions on phenylephrine global and regional hemodynamics effects remain unresolved.

The investigators assume that Phenylephrine may decrease cardiac output by increasing the afterload, while most likely could also make an increase or a stability of cardiac output by action on the venous return. The investigators propose an observational study assessing the influence of preload dependence, defined by the values of pulse pressure variation, on the effect of phenylephrine on cardiac output, measured beat by beat by esophageal Doppler.

The aim of the investigators work is to improve the understanding of phenylephrine action, a daily use therapeutic action, to improve the patients care.

Inclusion Criteria:

• Hypotension (SBP <90 mm Hg and / or MAP <60 mm Hg)
• Injection of a bolus of phenylephrine at the discretion of the anesthesiologist physician in charge of the patient.

Exclusion Criteria:

• Minor or major patient under guardianship
• Esophageal Diseases
• supra ventricular rhythm trouble
• Severe valvular
• Shunt intracardiac
• Vt <7ml/kg theoretical weight
• heart rate / respiratory rate <3.6
• Clinical hypepression of intra-abdominal
• Compliance <30 mL/cmH2O
• pulmonary hypertension, Right ventricular failure
• Spontaneous Ventilation
• Thorax open
• VG severe dysfunction (LVEF <40%)
• Prior Injection of ephedrine prior

General anesthesia.Orotracheal intubation and mechanical ventilation Advanced Hemodynamic Monitoring intraoperative ( arterial pressure catheter, esophageal Doppler)