Pain management for sedated ICU patients is complex, partly because of the difficulty of assessing pain in non-communicative patients, and partly because of the side effects associated with excessive use of morphine.

In this context, the use of another non-pharmacological approach, transcranial direct current stimulation (tDCS), could be of interest. With tDCS, neuronal activity is modulated by inducing a weak electric current through the cerebral cortex between two electrodes applied to the surface of the scalp. Although the mechanisms of action of tDCS are not yet fully understood, the medium-term effects are thought to be linked to the activation of N-methyl-D-aspartate receptors, glutamate-activated receptors involved in cellular memory. The use of tDCS as an analgesic therapy for chronic pain has produced encouraging results in patients suffering from fibromyalgia, migraine and central pain following spinal cord injury, Its use in sedated intensive care patients is unknown. To assess the possible analgesic effect of tDCS in these patients, we will use quantitative pupillometry, a technique already used in routine intensive care, to quantify nociception during a standardized nociceptive simulation.

Inclusion Criteria:

• Age from 18 to 80 years,
• Sedated patient requiring mechanical ventilation for at least 48 hours with administration of morphine.
• Person affiliated to the social security system or beneficiary of an assimilated regime.
• RASS ≤ -2
• Close consent or emergency inclusion

Exclusion Criteria:

• History of epilepsy.
• Severe brain injury (head trauma, stroke, neuromeningeal infection, status epilepticus).
• Presence of intracranial ferromagnetic material.
• Presence of electronic stimulators or implants (e.g. pacemaker, spinal cord or intracranial stimulator).
• Facial trauma preventing eye opening.
• Patients who are blind and/or have eye damage.
• Protected persons: pregnant women, parturients, nursing mothers, persons deprived of their liberty by judicial or administrative decision, persons under legal protection.
• Subjects excluded from another study.