The aim of this study was to assess the out-of-plane versus the in-plane approaches for the interscalene brachial plexus block; as regards the performance time, the onset, the progression and the recovery of sensory block, the onset and progression of the motor block as well as, the postoperative pain score and the duration of analgesia for arthroscopic shoulder surgery. A total of 60 patients of American Society of Anesthesiologists (ASA) physical status I-II were randomly divided to receive either the in-plane approach (Group I), or the out-of-plane approach (Group O).

60 patients of ASA physical status I - II, greater than or equal to 30 years old and smaller than or equal to 60 years old, scheduled to undergo arthroscopic shoulder surgery in the lateral position; under ultrasound -guided interscalene brachial plexus block (ISPB) in this randomized study at Ain-Shams University Hospitals. On arriving to the operating theater, patients had an 18G intravenous cannula inserted in the non-operative upper limb side. All patients received; 0.05 mg/kg IV midazolam hydrochloride and 30 mg pethidine. Intraoperative basic monitors were applied using 5-leads ECG, pulse oximetry, non-invasive blood pressure (NIBP) and capnography (sample tube inserted under the O2 mask).A simple O2 mask at a flow of 6L/min was applied. Infusion of Ringer's solution was then started at a rate of 5mL/kg/h throughout the surgery. Patients were placed in the supine position with their heads rotated towards the non-operative side. Iodine solution was used as an antiseptic on the operative neck side and then the patient head, neck and chest were draped. Local infiltration of the skin at the point of needle insertion was carried out with 2 ml lidocaine hydrochloride 1%, then a sterile 50-mm 22-G insulated needle was used for performance of the block.The ultrasound with a high frequency linear transducer was used, with the depth setting of 2-4 cm. Distal to proximal (Trace back) approach was used; the supraclavicular fossa was scanned first to identify the subclavian artery as it passes over the first rib; by placing the probe against the clavicle and scanning in a caudate direction. The brachial plexus was easily identified as bunch of grapes supero-lateral to the artery. The plexus was followed medially and cephalad along its course by keeping the nerves in the center of the screen, to identify the brachial plexus roots between the anterior and the middle scalene muscles at the level of the sixth cervical vertebra deep to the sternocleidomastoid muscle.

Patients were then divided into 2 equal groups of 30 patients each:

Group I: An in-plane approach was used for the interscalene block. The needle was brought in the same plane as the probe at a shallow angle to the skin, some distance away from the edge of the probe in a lateral to medial direction so that the whole length of the needle can be visualized. After negative aspiration and assurance that high resistance to injection was absent, the LA was injected in a 5 ml increment below the lower root, between the 3 roots and above the upper root.

Group O: An out-of-plane approach was used for the interscalene block. The needle was inserted cranial to the probe and after negative aspiration and assurance that high resistance to injection was absent, the LA was injected in a 10 ml increment; lateral and medial to the nerve roots. The needle appeared as a bright dot on the screen and by tilting the probe, the tip was identified as the point where further tilting leads to no longer visualization of the bright dot on the screen.

After completion of the LA administration, the time was recorded as a baseline for the time interval. The assistant who recorded the data was blind to the patient groups. The sensory block was assessed by a pin-prick test using a 3-point scale. The motor block was assessed according to the shoulder, arm and fingers movement using a 3-point scale. Postoperative pain was measured at rest using the VAS score

Inclusion Criteria:

• ASA physical status I - II
• scheduled to undergo arthroscopic shoulder surgery in the lateral position

Exclusion Criteria:

• body mass index ≥ 35 kg/m2 body surface area
• anticipated difficult airway
• infection at the injection site
• known LA allergy,
• contralateral phrenic nerve dysfunction
• history of cardiac disease
• history of hepatic disease
• history of renal disease
• coagulopathy
• chronic obstructive pulmonary disease
• neuropathy involving the brachial plexus.