Rationale: Diligent fluid management is instrumental to improve postoperative outcome, cost and quality of care.

Objective: To determine the accuracy of brachial, femoral and carotid blood flow measurement with ultrasound compared to intermittent transpulmonary thermodilution cardiac output measurement, invasive and non-invasive pulse-contour analysis.

Study design: Observational study - Prospective clinical non-intervention measurement study.

Study population: Adult ASA 1-2 patients, scheduled for open upper GI surgery Intervention (if applicable): Not applicable. We will perform non-invasive ultrasound measurements of the femoral, carotid and brachial blood flow right before induction and under anaesthesia.

Main study parameters/endpoints: Femoral, carotid and brachial blood flow determined by ultrasound and blood flow variation and the accuracy compared to transpulmonary thermodilution cardiac output, stroke volume variation, and pulse-contour analysis derived cardiac output (invasive or non-invasive) at the following time points during surgery; (limited for femoral site as it cannot be measured during surgery): (1) before induction of anaesthesia, (2) after induction, (3) 15 minutes after start of surgery, (4) before and (5) after (1-2 minutes) a fluid bolus, (6) before and (7) after start of vasopressors, (8) before and (9) after Trendelenburg position and (10) after surgery before end of anaesthesia (figure 1). A fluid bolus will be performed as part of standard care (goal-directed fluid therapy). The vasopressor and Trendelenburg position time points are optional measurements. We will also measure (continuous) invasive femoral blood pressure (SBP, DBP, MAP), non-invasive blood pressure, SVV, central venous pressure (when available), heart rate, SpO2, PFI, etCO2.

Inclusion Criteria:

• Elective open GI surgery
• Invasive arterial blood pressure monitoring
• Informed consent

Exclusion Criteria:

• Significant stenosis > 30% or abnormal anatomy of aortic, femoral, carotid or brachial artery
• Cerebrovascular accident
• Atrial fibrillation
• COPD stage 3-4
• Lobectomy / pneumectomy
• Active pneumonia
• Cardiac failure
• Severe heart valve regurgitation or stenosis
• Not able to measure brachial or carotid artery blood flow during surgery
• Contra-indications for femoral arterial catheter placement (e.g., vascular graft)

Adult patients, scheduled for open upper GI surgery with a American Society of Anaesthesiologist score of 1 to 2

Plan to make individual available upon request