After conduction a pilot study, pupillary dilation reflex (PDR) is measured in response to nociceptive stimulation perioperatively.

An infrared camera of the video pupillometer measures the pupillary dilation reflex (PDR) in response to incremental nociceptive stimuli. The PDR is a robust reflex, even in patients under general anesthesia, and may provide a potential evaluation of the autonomous nociceptive circuit. American Society of Anesthesiologists (ASA) classification I or II patients undergoing elective surgery under general anesthesia are recruited. Enrolled patients perioperative undergo PDR measurement at 2 different standardized times (before and after opioid administration) generated by an inbuilt pupillary pain index (PPI) protocol. PPI, as a surrogate for nociception includes noxious stimulations from 10 up to 60 milli ampere (mA) until pupil dilation is larger than 13% from baseline diameter. Therefore, no inappropriate high stimulation is executed.

Inclusion Criteria:

• Scheduled abdominal or gynecological surgery
• ASA I-II

Exclusion Criteria:

• History of eye deformity, invasive ophthalmologic surgery
• Known 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
• Preoperatively administrated benzodiazepins or antiemetics