Dysfonction of the device

The investigators want to test during anesthesia the feasibility of a closed-loop automated fluid replacement system using cardiac output monitoring as the input value.

The optimization of the cardiac output is an important goal during anesthesia to decrease the postoperative morbidity, mortality and the care costs.

We want to test if the closed-loop fluid administration is feasible.

Two groups will be compared. In all cases:

• anesthesia will be provided by a closed-loop which aim is to maintain bispectral index between 40 and 60 using propofol and remifentanil. This method permits to have similar depths of anesthesia in all cases.
• cardiac output will be continuously monitored by LidCO. In one group, fluid replacement is decided by the physician; in the other, fluid replacement is automated using a closed-loop system.

Inclusion Criteria:

• Adult patients aged 18-75 years
• Scheduled for abdominal surgery under general anesthesia and requiring an invasive arterial blood pressure monitoring
• Consenting to participate in the study

Exclusion Criteria:

• Pregnant, breast feeding women
• Allergy
• Pacemaker
• Psychiatric disease, dementia, brain disease
• Contraindication to hydroxyethyl starch
• Inability to measure pulse pressure variability : arrhythmia, spontaneous breathing, or tidal volume < 7 ml/Kg