Rationale: Postoperative pain management after transaxillary thoracic outlet decompression surgery (TATOD) is difficult. In a retrospective case-control trial, we found evidence that a PECS II block is able to reduce pain and morphine consumption. This may ultimately lead to less morphine induced side-effects and improved patient satisfaction. However, the risk of bias in retrospective research is high. To determine the effect of PECS II in TATOD, a randomized controlled double blinded trial could offer more valuable scientific evidence. Our hypothesis is that a PECS II block will reduce pain, opioid use and opioid induced side-effects in patients undergoing transaxillary TOD (TATOD).

Objective: The aim of the study is to determine the effect of a PECS II block on postoperative pain and opioid use in patients undergoing TATOD. The secondary objective is to determine the effect of a PECS II block on opioid induced side effects such as postoperative nausea and vomitus and the quality of recovery Study design: Single centre randomized controlled double blinded trial Study population: All patients with Neurogenic Thoracic Outlet Syndrome (NTOS) selected for TATOD by the TOS multidisciplinary workgroup and based on the specifications in 2016 SVS reporting standards.

Intervention: The study group will receive a PECS II block with 40 ml ropivacaine 5 mg/ml. The control group will receive a PECS II block with 40 ml NaCL 0.9%.

Main study parameters/endpoints: Primary outcome parameters are postoperative pain using the Numeric Rated Scale (NRS) score assessed at rest and when moving and postoperative morphine-equivalent consumption. Secondary outcome parameters are postoperative Nausea and Vomitus (PONV) and Quality of Recovery questionnaire (QoR-15).

Nature and extent of the burden and risks associated with participation, benefit and group relatedness: All patients will undergo ultrasound guided injection, after induction of anaesthesia. The administration of the injection does not invoke any extra physical discom-fort. Possible complications include hematoma and pneumothorax, however, the risk is very low (<1%)[1]. In the intervention group, we expect less pain, a reduced need for pain medica-tion and less postoperative nausea and vomitus. We do not expect an altered postoperative course in the control group. Patients will be asked to fill out a questionnaire. Extra blood sam-ples, site visits, physical examinations or other test will not be done in this study.

Inclusion Criteria:

• Patients with NTOS
• Selected for a trans-axillary thoracic outlet decompression (TATOD) by the TOS multidisciplinary workgroup.
• Fit for surgery, defined as ASA (American Society of Anesthesiologists) Classification of I, II or III.
• 18 years of age or older
• Sufficient in speaking and writing the Dutch language
• Normal liver and renal function
• Informed consent

Exclusion Criteria:

• Patients with a history of TOD (Redo-surgery)
• Patients with ATOS or VTOS
• ASA ≥ 4
• Kidney or liver failure with contra-indication for NSAID or paracetamol
• Mental retardation
• Pregnancy
• Patients with chronic strong opioid use (>3 administrations per week or continuous transdermal therapy, longer than the last 3 months)
• Allergy to one or more medications used in the study including, ropivacaine, dexamethasone, propofol, sufentanil, succinylcholine, paracetamol, NSAID, morphine, granisetron
• Patients that have trouble expressing themselves in Dutch. Questionnaires are completed by the patients and checked by the nurses. The questionnaire is in Dutch. If there is a language barrier between the questionnaire, the patient or the health care worker, we believe the validity of the answers is questionable.

Randomisation will be performed by an independent pharmacist from the hospital pharmacy before the start of the trial. This pharmacist has no other task then creating this list and overseeing the preparation of the syringes used in this trial. Syringes will be prepared with ropivacaine or placebo based on this randomisation list. This syringe will be delivered to the preoperative holding with a label that clearly states BLOCKTOS medication, patient name, date of birth and patient number. This procedure makes sure that the patients, surgeons, anaesthesiologist and any other medical personnel are blinded for the randomisation.