The aim of the study was to describe the feasibility of the nociception flexion reflex and the pupillary dilatation reflex as objective pain assessment tools in the Intensive Care Unit (ICU). Furthermore to describe the relationship between the responses and the standard of care pain evaluation in the critically ill sedated patients.

Patients were under propofol / remifentanil or propofol / sufentanil sedation protocol during measurements in a stair-case increasing intensity model of standardized stimulations. (Stimulation intensity are similar to the stimulations of neuromuscular blocking agents monitoring.)

Pupillary dilatation reflex: tetanic stimulations at the nervus medianus were performed starting form 10 milliamperes (mA) up to 60mA. Pupillary diameter was measured before, during and after stimulation.

Nociception flexion reflex: tetanic stimulations at the nervus suralis were performed starting form 0.5mA in increasing steps via an automated RIII (NFR) threshold tracking model.

Inclusion Criteria:

• 18 years of age or older
• Critically ill with necessity to mechanic ventilation
• Hospitalized at the ICU of our institution
• Started sedation protocol (propofol/remifentanil or propofol/sufentanil)
• Approved informed consent by family member or relative.

Exclusion Criteria:

• Known eye deformity or extented ophthalmologic surgery in history
• Severe traumatic brain injury of fulminant stroke
• Known (poly)neuropathy of complicated diabetes
• Need for continuously curarization
• Hemodynamic instability