Few works have studied the area of analgesia covered by the spinal erector block in an objective manner, especially on the cephalo-caudal spread. The available data are dissection works or subjective data such as thermoalgesic or epicritic sensitivity.

This information would however be relevant in order to propose a better analgesia. Indeed, it could explain certain failures by insufficient diffusion of the block. The use of a multistage block could be relevant, especially in the case of osteosynthesis on several vertebral levels.

Pupillometry makes possible to monitor analgesia based on the pupillary dilation reflex to pain. The goal is to establish an objective mapping of these type of analgesia from these data.

Inclusion Criteria:

• Patients receiving erector spinae block for pain management of spinal osteosynthesis

Exclusion Criteria:

• Patient refusal
• Known allergy to local anesthetics
• Contraindication to locoregional anesthesia (haemostasis disorder, infection, peripheral neuropathy)
• Technical impossibility to perform a spinal erector block
• Pathology with dysautonomia altering the pupillary reflex: diabetes mellitus with diabetic retinopathy, multiple sclerosis, systemic amyloidosis, uncontrolled hypertension, glaucoma
• Current treatment likely to alter pupillary dilation reflex to pain : antiemetic (droperidol, metoclopramide), alpha-2 agonist (clonidine)
• Serious psychiatric history
• Drug abuse
• Pregnancy

Patients receiving erector spinae block for pain management of spinal osteosynthesis will be included.