This prospective, observational study was approved by the institutional review board, and registered before patient enrollment (the Clinical Trial Registry of Korea: https://cris.nih.go.kr/cris/index.jsp, Identifier: KCT0003125, Principal investigator: Chunwoo Yang, Date of registration: 8.22.2018). Adult inpatients (20—80 years of age, American Society of Anesthesiologists physical status 1—3) scheduled for arthroscopic shoulder surgery were considered eligible for inclusion. Patients with severe respiratory disease, contraindication to regional anesthesia, body mass index > 35 kg/m2,pre-existing neuropathy, allergy to study medications, or pregnancy were excluded. All patients provided written informed consent and were fully informed of the risks and benefits of participating, including the risk of block failure and the potential need to repeat the procedure.
ASA monitoring was applied along with supplemental oxygen upon arrival to the induction room and utilized throughout the procedure. All blocks were performed by the same anesthetist. We used an ultrasound (US) system (Vivid q, GE Healthcare, WI, USA) with a high frequency linear probe (6—13 MHz) for guidance. Blocks were performed with a 50 mm insulated needle (UniPlex NanoLine, Pajunk, Geisingen, Germany) using a nerve stimulator (MultiStim, Pajunk) for localization. All patients received intravenous (IV) midazolam (1—3 mg) and fentanyl (25—50 µg) for sedation and anxiolysis before the block.
The CCB was performed first using a previously described technique . Patients were positioned supine with the head turned to the contralateral side. The US probe was initially placed below the clavicle and over the medial infraclavicular fossa. Subsequently, the probe was tilted slightly cephalad to visualize the costoclavicular space and the three cords of the brachial plexus. After skin infiltration, the needle was advanced under US guidance in-plane and from a lateral-to-medial direction until its tip was located in the middle of all three cords. After negative aspiration, 12 ml ropivacaine 0.5% was slowly injected.
Proximal SSNB was performed using previously described techniques . Patients were positioned supine with the head turned to the contralateral side. Under sterile conditions, the US probe was placed in the lateral side of the neck at the level of the cricoid cartilage. The suprascapular nerve was traced distally from the superior trunk or C5 nerve root to select a puncture site as far lateral as possible to avoid local anesthetic (LA) spread to the supraclavicular brachial plexus. This nerve is usually located underneath the omohyoid muscle at the supraclavicular fossa. After skin infiltration, the needle was advanced in a lateral-to-medial direction using an in-plane technique until the tip was positioned at the suprascapular nerve. After confirming sustained muscle contraction with the nerve stimulator (> 0.2 mA), 8 ml ropivacaine 0.5% was slowly injected after negative aspiration. If the nerve was not visualized or stimulation did not elicit an appropriate motor response, LA was injected underneath the omohyoid muscle.
During block placement, block performance time, number of needle passes, patient discomfort, and any adverse events (such as vascular puncture, LA toxicity, and unintentional paresthesia) were recorded by the anesthesia nurse assisting the anesthetist performing the block. Block performance time was defined as the time from first block needle insertion to the end of the second block LA injection. The initial needle insertion was considered as the first pass. Any subsequent needle advancement that was preceded by a retraction of at least 10 mm counted as an additional pass. Patient discomfort during block placement was assessed using a numerical rating scale (NRS) with range 0—10 (0, no pain; 10, worst imaginable pain).
Motor block (shoulder abduction for axillary nerve and shoulder external rotation for suprascapular nerve) was clinically assessed 30 min after block placement with a three-point scale (0, no block; 1, paresis; and 2, paralysis). Since the suprascapular and subscapular nerve typically do not contain cutaneous afferent fibers , sensory block of all nerves related to the shoulder joint was not tested. A successful block was defined as a patient discomfort rating of 0 in the post-anesthesia care unit (PACU) at 30 min with a block duration of more than 6 hr postoperatively. Block duration was defined as the time interval between the end of the LA injection and the first pain sensation.
Diaphragmatic excursion was assessed before and 30 min after nerve blocks. With the patient in a supine position, a 4-MHz curvilinear US probe was used to perform the scan from a low intercostal or subcostal approach, using the liver on the right or spleen on the left as an acoustic window. Diaphragmatic excursion was measured during deep inspiration using M-mode ultrasonography. Complete, partial, and no diaphragmatic paralysis were individually defined as decrease between 75% and 100% (including the occurrence of paradoxical movement), decrease between 25% and 75%, and a decrease of < 25% in diaphragmatic excursion, respectively.
All patients received general anesthesia using IV propofol (1—2 µg/kg) with endotracheal intubation facilitated by IV cisatracurium (0.1—0.2 µg/kg). Anesthesia was maintained using an air/oxygen mixture and 2—3% sevoflurane. IV fentanyl (1—2 µg/kg) was administered when blood pressure increased by > 20% over the preoperative blood pressure. At the conclusion of surgery, residual paralysis was antagonized with pyridostigmine and glycopyrrolate if required.
In the PACU, resting pain score at 30 min was assessed, and use of supplemental analgesia was recorded. Patients with block failure were offered the option of either rescue ISB or IV fentanyl for adequate pain control. Postoperatively, all patients received 1 g of IV paracetamol every 6 h and 30 mg of IV ketorolac every 12 h for the first 24 h after surgery irrespective of pain status. For rescue analgesia, patients were instructed to request analgesics (meperidine 25 mg IV) if their pain score was greater than 4.
The primary outcome was resting postoperative pain at 30 min in the PACU. Secondary outcomes included procedure-related outcomes, the occurrence of phrenic nerve palsy, motor block, pain score at 6 h and 24 h after surgery, block duration, use of supplemental analgesia in the PACU and surgical ward, patient satisfaction as assessed by a NRS (range 0—10; 0, dissatisfied; 10, very satisfied), and any adverse events (paresthesia, dyspnea, and handgrip weakness).
Since most distal nerve blocks for shoulder surgery usually result in inferior analgesia in the immediate postoperative period, the primary outcome of this study was the patient discomfort score in the PACU at 30 min. Assuming a noninferiority margin of 1.5 points and a standard deviation (SD) of 1.7 based on a previous study , the necessary sample size for α = 0.05 and 80% power was calculated to be 16 patients. To allow for possible dropouts, we included 20 patients.
Descriptive statistics were used to summarize the data, which are presented as means (SD), medians (interquartile range), or numbers (percent) where appropriate. Statistical analyses were performed using SPSS 19.0 version software (IBM, Armonk, NY, USA).