The first purpose of this study is to compare the effectiveness of the stellate ganglion block realized with two different approaches (blind and ultrasound-guided) in patients with a diagnosis of complex regional pain syndrome.

The second purpose of this study is to determine the safest approach and to compare the safety profiles of the two approaches.

To evaluate whether the ultrasound guided approach is more effective than the blind technique in producing a greater than 1.5 degree Celsius rise in ipsilateral arm temperature after a stellate ganglion block.

Blocks will both be performed with 10 mL of xylocaine/bupivacaine. Secondary outcomes will be the impact of the approach (blind vs ultrasound) on pain reduction, horner syndrome, side effects (hoarseness, dysphagia, pharyngeal discomfort) and complications (blood aspiration, intravascular injection).

Inclusion Criteria:

• Patients aged 18 to 80 years
• Patients with a new or known diagnosis of complex regional pain syndrome (according to the criteria of Budapest) at the upper extremity

Exclusion Criteria:

• Refusal of a patient
• Coagulopathy
• Systemic infection or local infection at the needle injection site
• Major deformation at the level of the neck (radiotherapy, surgery, etc. )
• Concomitant chronic pain syndrome
• Post-pneumonectomy on the controlateral side
• Severe hepatic impairment or severe renal impairment (Clcr under 30 ml/min)
• Known allergy to local anesthetics of amide type
• Inability to understand a numeric pain scale