Diastolic function may be evaluated by different measurements on transesophageal echocardiography (TEE). They include mitral inflow velocities obtained by pulsed-wave doppler (PW) : peak early diastolic velocity (E) and late diastolic velocity (A). Mitral annulus velocities, early diastolic (e') and late diastolic (a') are obtained by tissue doppler imaging (TDI). The ratio E/e' reflects left ventricular filling pressure and, as such, might be a predictor of fluid responsiveness.

The aim of this study is to evaluate the predictive value of the mitral valve E/e' ratio for fluid responsiveness among patients undergoing coronary bypass graft surgery. Fluid responsiveness being defined as an increase in stroke volume of ≥ 15%.

After induction of anesthesia, patients will have their diastolic function evaluated by means of E/e' and other measures. They will then be administered an intravenous bolus of 500 mL of Lactate Ringer® along with passive leg raising (PLR). Stroke volume and fluid responsiveness will be assessed by the thermodilution method (Swan-Ganz catheter) and the FloTrac® device. Fluid responders will be compared to non-responders to evaluate the relationship between E/e' ratio and fluid responsiveness.

Inclusion Criteria:

• Patients >18 yrs, undergoing elective coronary artery bypass grafting or surgery will be included.

Exclusion Criteria:

• Significant mitral valvular heart disease (mitral regurgitation ≥ 2/4 or stenosis)
• Significant right sided valvular heart disease (tricuspid regurgitation ≥ 2/4)
• Intracardiac shunts
• Emergency surgery
• Non-sinusal rythme
• Clinical evidence of decompensated heart failure
• Clinical evidence of decompensated pulmonary hypertension
• Renal insufficiency with creatinine clairance ≤ 30 cc/min or dialysis
• Contraindications to TEE, including esophageal disease or unstable cervical spine
• CVP ≥ 15 mm Hg or PCWP ≥ 18 mm Hg immediately before fluid infusion