Journal für Anästhesie und Intensivbehandlung 2. Ausgabe 1995

Interscalene brachial plexus block

N. E. Sharrock


At our institution, we perform about 1000 interscalene blocks per annum, mainly for shoulder surgery. It is the standard technique used. Blocks are performed seeking paresthesia with 45-55 mL local anesthetic with few complications and over a 95 % success rate. (7)


The interscalene block entails anesthetizing the brachial plexus at the level of the nerve roots of C5-6 or superior trunk as it lies between the anterior and medial scalene muscles in the neck. This technique was developed by Dr. Alon Winnie.(1)


The nerve roots C2 through T1 exit the intervertebral foraminae and lie in a fascial plane created by the anterior and medial scalene muscles. Injection of local anesthetic into this plane results in spread within this layer both rostrally towards C2 and caudally toward T1. Interscalene block is typically performed at the midpoint C5-6 so that spread upward involves the upper cervical plexus (C2-4) and downward affects the brachial plexus (C5-T1).


The essence of this technique is to gain an appreciation of the topical anatomy of the muscles of the neck. The first muscle to locate is the sternocleidomastoid which lies in the anterolateral neck extending from the mastoid process to insert medially on the sternum and laterally on the clavicle. The lateral insertion varies - sometimes being quite lateral. The belly of the sternocleidomastoid should be located with the index finger placed at the posterior margin at the level of the junction of the middle and lower thirds. The finger now lies in the groove between the sternocleidomastoid anteriorly and the anterior scalene posteriorly. The most common error in performing interscalene block is to assume this is the interscalene groove. The belly of the anterior scalene is usually 1/2 - 1 cm wide. The finger is then rolled posteriorly over the anterior scalene to rest in a narrow groove between the anterior and middle scalene muscles. To verify this groove, one can ask the patient to take a deep breath which highlights the groove as the scalene muscles are muscles of respiration and contract during deep inspiration.(2)

Once the groove is located, the index finger remains in the groove and a 23 gauge needle advanced slowly between the muscle bellies (into the middle of the groove). The patient is asked to report any sensation and locate it - whether in the neck, the anterior chest just below the clavicle, to the back over the shoulder blade, to the top of the shoulder, or into the arm. As soon as any sensation to the tip of the shoulder or down the arm is perceived, the needle is stabilized and the local anesthetic injected in 5 mL increments, aspirating between injections to verify absence of intravascular location. If upon injection, the patient experiences discomfort or the local anesthetic is at all difficult to inject, the needle should be withdrawn 1 mm or rotated and the injection continued.

The technique described is performed in a non-sedated awake patient by eliciting a paresthesia to either the tip of the shoulder, (3) arm, or hand. Alternatively, the patient can be sedated and the nerves located using a nerve stimulator to elicit a C6 (biceps) motor response. We prefer to perform this in awake patients, but this requires skill and good communication with the patient. It is important to talk to the patient, to have them relax so that the muscles are not too tense as the platysma may be confused with the scalene muscles. It is also preferred not to rotate the head more than 20° to the contralateral side as this puts too much tension on the sternocleidomastoid.

Winnie described inserting the needle into the groove at 90° to all planes of the neck.(1) This works if the neck is flexed on a pillow. If the head is somewhat extended (no pillow), the scalene muscle are in a plane more parallel to the bed so that the needle should enter the groove parallel to the bed (in the plane of the groove). An appreciation of how the interscalene muscle are lying in the neck helps one direct the needle.

If one obtains a paresthesia to the anterior chest below the clavicle, the needle is most likely in the anterior scalene so the needle should be redirected more posteriorly to enter the interscalene groove. On the other hand, if a paresthesia is obtained to the back of the shoulder, the needle is probably in the medial scalene. The needle should then be redirected more anteriorly to locate the brachial plexus.

The landmarks of the sternocleidomastoid and scalene muscles vary between individuals. Some are thin with long necks and the landmarks are easy to feel. Others have short bull necks and the landmarks are hard to find. Muscle may be hypertrophied in certain patients and in patients with respiratory disease. In these situations, the interscalene groove may lie somewhat beneath the sternocleidomastoid.


Winnie originally described using doses as low as 20-30 mL of local anesthetic. This will reliably anesthetize the superior and middle trunks but not the inferior trunk. I usually inject 45-50 mL l.5 % mepivacaine with epinephrine 150 g plus bicarbonate.(3) This provides a solid brachial plexus block for shoulder surgery in all cases without toxic effects of local anesthetics. Skin infiltration will be required for posterior portals (for arthroscopy) and for surgical incisions which extend toward the axilla as the T2 innervations (of the intercostobrachial nerves) are not anesthetized with this block.

Assessment of Block

Within minutes, the patient cannot raise the arm against gravity and shortly thereafter the elbow cannot be flexed.(3) The ability to move the fingers is retained for much longer. The hand warms up, reflecting the sympathetic block - initially the thumb and with time, the ring and little finger. The effectiveness of the block is readily assessed by these motor and sympathetic responses.

Physiological Effects

Cervical plexus block occurs in all cases so that ipsilateral diaphragm paresis occurs uniformly. (4) This results in an average reduction of 20-40 % in vital capacity. (5) This is well tolerated in most patients. However, we use nasal oxygen during surgery, monitor SaO2 and do not perform the blocks in patients with vital capacity of less than 1.5 - 2 liters. With this approach, we have not seen respiratory insufficiency.

There is a sympathectomy of the head and neck. This results in a unilateral Horner's syndrome with ipsilateral ptosis and stuffy nose (from vasodilation of the nasal mucosa). Most patients also develop a change in voice (so-called hoarseness) to a variable extent. This has been attributed to vocal cord paralysis but is more likely due to vasodilation of one side of the pharynx, altering its ability to vibrate thus creating different oscillation characteristics and a change in voice.

Clinical Uses

Interscalene block is best suited for surgery of the shoulder. It can be also used for surgery of the arm and elbow. Surgery of the forearm and hand is probably easier to perform with axillary block.

Interscalene block can also be used for surgery of the neck (carotid endarterectomy), clavicle, shoulder girdle, and exploration of the brachial plexus.(6)


Intravascular injection of excessive doses of local anesthetic can lead to seizure. Injecting too far caudally with the needle directed laterally can lead to pneumothorax. However, with proper interscalene block technique, it is impossible to get a pneumothorax. Injection close to the intervertebral foramina can result in conduction anesthesia (epidural or subarachnoid spread). This, however, is rare.

Anaesthesie, Plexus brachialis Blockade, interscalenär


Dr. N.E. Sharrock
Dept. Anaesthesia
Hospital for Special Surgery
515-E. 72nd Street
New York
NY 10021

[1] Winnie AP. Interscalene brachial plexus block. Anesth Analg 1970; 49:455-466

[2] Sharrock NE, Bruce G. An improved technique for locating the interscalene groove. Anesthesiology 1976; 44:431-433

[3] Roch JJ, Sharrock NE, Neudachin L. Interscalene brachial plexus block for shoulder surgery: A priximal paresthesia is effective. Anesth Analg 1992; 75:386-388

[4] Urmey WF, Talts KH, Sharrock NE. One hundred percent incidence of hemidiaphragmatic paresis associated with interscalene brachial plexus anesthesia as diagnosed by ultrasonography. Anesth Analg 1991; 72:498-503

[5] Urmey WF, McDonald M. Hemidiaphragmatic paresis during interscalene brachial plexus block: effects on pulmonary function and chest wall mechanics. Anesth Analg 1992; 74:352-357

[6] Sharrock NE, Hotchkiss R, Ennis WJ III, Weiland A. Brachial plexus surgery via the infraclavicular approach performed under interscaldene block. (accepted for publication) J Hand Surg 1995

[7] King RS, Urquhart B, Urquhart B, Sharrock NE. Factors influencing the success of brachial plexus block. Reg Anesth 1991; 16:63

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