In this study, the pupillary dilation reflex is measured as a nociceptive indicator during elective abdominal surgery under general anesthesia.

An infrared camera of the video pupillometer measures the pupillary dilation reflex (PDR) in response of a nociceptive stimulus. This autonomic reflex, parasympathetic mediated in sedated patients, can be generated by various pain stimuli (built in standardized protocol, surgical incision, …) The PDR is a robust reflex, even in patients under general anesthesia, and provides a potential evaluation of the autonomous circuit within the nociceptive evaluation based on pupil dilation upon A-delta and C fibers in both electrical or mechanic stimulation. This mono-centric project involving American Society of Anesthesiologists (ASA) classification I-II patients undergoing elective abdominal surgery under general anesthesia are recruited. Enrolled patients perioperative undergo PDR measurements at four different standardized times.

Inclusion Criteria:

• Scheduled abdominal surgery
• ASA I-II

Exclusion Criteria:

• History of eye deformity, invasive ophthalmologic surgery, impaired pupil reflex in advance
• Kown cranial nerve(s) deficit
• Infection of the eye
• Predicted difficult airway management (DAF Guidelines)
• Chronic opioid use (>3 months)
• Ongoing treatment with beta-blockers, dopamine antagonists, topical atropine