too difficult to measure sublingual microcirculation continuously during a fluid challenge

The goal of this prospective observational study is to assess the impact of fluid challenge administration on macro and microcirculation in patients situated in the gray zone during a high risk abdominal surgery

Fluid optimization is a key goal in anesthesia. It allows to titrate fluid bolus based on flow variables or dynamic parameters of fluid responsiveness (pulse pressure variation (PPV) or stroke volume variation (SVV)).

When PPV or SVV is above 13%, the patient will usually respond to a bolus of fluid while when PPV or SVV is below 9%, the patient will normally not respond to it. Between 9% and 13%, it is a gray zone where the effect of a fluid bolus is uncertain.

The overall goal of fluid bolus administration is of course to optimize macrocirculation (stroke volume and cardiac output) but also (and probably more importantly) end organ tissue perfusion. However, regional tissue perfusion is not widely monitored during surgery. However, we do have some monitoring tools to assess microcirculation at the bedside.

Investigation of microcirculation in addition to macro circulation may allow clinicians to know if a patient situated in the gray zone may or not increase microcirculation variables while macrocirculation variables are well known to be of little value to predict fluid responsiveness.

The goal of this study is to assess microcirculation variables in patients situated in the gray zone (PPV between 9%-13%), and to assess macro and microcirculation responses to a standardized fluid challenge of 4 ml/kg of a balanced crystalloid solution.

Inclusion Criteria:

• Patients undergoing a high-risk abdominal surgery
• Patients equipped with a minimally invasive cardiac output monitoring device in order to optimize fluid administration

Exclusion Criteria:

• Atrial fibrillation
• Ejection fraction <40%

Patients scheduled for a high-risk abdominal surgery and equipped with a minimally uncalibrated pulse contour analysis monitoring device as part of their anesthetic care.

All patients will have the hemodynamic monintoring to assess macrocirculation and sublingual microcirculation.