Interscalene Brachial Plexus Block
Scott Pearson & Eric Petrunak
(Original Authors: Brown, Novak, Underwood, 2003)
Diagram obtained from Brown, Novak, & Underwood 2003 Anesthesia
Class Project PowerPoint on Interscalene Plexus Block.
Indications
The interscalene approach is used for surgical procedures of the shoulder or upper arm
and blocks brachial plexus nerves. The interscalene block is useful for post-operative pain
control and is commonly utilized in conjunction with general anesthesia but can be used alone.
The interscalene approach to brachial plexus block is most intense in the C5-C7 dermatomes and
least intense in the C8-T1 dermatomes, therefore surgical anesthesia is not optimal for areas of
ulnar innervation. This block can also be used for pain management of shoulder arthrosis,
arthritis, and complex regional pain syndromes.
Drugs
Bupivacaine 0.25% or 0.5% is frequently used. The 0.25% has an onset of 20-30 minutes
and duration of 7-15 hours. The 0.5% has an onset of 10-20 minutes and duration of 9-20 hours.
Epinephrine does not prolong the duration of Bupivacaine. 0.1cc of sodium bicarbonate per 10cc
of local can hasten the onset time. Bupivacaine is frequently used since it has a long duration to
provide post-op analgesia. Other drugs that can be used include: Procaine 2%, Chlorprocaine
2%, Lidocaine 1%, Mepivacaine 1%, and Prilocaine 1%. These other drugs are less frequently
used as they have much shorter duration of actions, even with Epinephrine, therefore are less
optimal for post-op pain control. 20-40 cc of local anesthetic is used depending on extent of
block required, patient condition, and the stature of the patient.
Anatomy
The brachial plexus includes spinal nerves C5-T1. The brachial plexus may contain C4
and T2 as well. Cervical spinal nerves blend into trunks between the anterior and middle scalene
muscles. Brachial plexus cervical nerves pass laterally in a deep groove in the superior surface of
the cervical vertebrae transverse process. This groove separates the transverse process into
anterior and posterior tubercles. These tubercles are the origin of the anterior and medial scalene
muscles. In a normal person the C6 transverse process is superficial and no more than 1.5-2 cm
beneath the skin. The scalene muscles pass under the midpoint of the clavicle and insert on the
1st rib. The subclavian artery runs between the anterior and middle scalene muscles. Refer to the
anatomy website for further shoulder and brachial plexus anatomy.
http://www.pitt.edu/~anat/Extremities/Shoulder/Shoulder.htm
Technique
The patient is supine with the head flexed, not rotated, to the contralateral side. A towel is
placed under the head and the patient is asked to hold the ipsilateral shoulder down as though
reaching for the knee. The external jugular often crosses the interscalene groove at the level of
the cricoid cartilage. The SCM is palpated first. With the patient raising his head in a sniffing
position the scalene muscle stiffens. The interscalene groove between the anterior and medial
scalene is found by rolling the fingers off the lateral edge of the SCM. The groove can be felt at
the peak of deep inspiration as the scalenes are accessory muscles of ventilation. The groove is
palpated as high as possible. The patient can then relax and the level at the cricoid is marked.
The transverse process of C6 can usually be palpated and is directly opposite to the entry point.
The site is cleaned and prepped with a povidone-iodine solution 2 inches in circumference to the
injection site. A skin wheal is performed with plain 0.5% Lidocaine. A 22G 1.5inch B bevel
needle is introduced perpendicular to the skin (not perpendicular to the spinal axis) until a
distinct pop is felt indicating penetration of the fascia. The needle is advanced in medial and
caudal directions until a parethesia or evoked muscle contraction in the arm is elicited. Evoked
muscle contraction can be accomplished by attaching the negative cathode of a PNS to the
needle with an alligator clip. The positive cathode is attached to an EKG electrode on the chest.
Set the PNS to 5-10 mA and advance the needle until cyclic muscle contraction at or distal to the
shoulder is noted. Reduce the current to 0.5-1 mA and slowly advance/withdraw the needle until
maximum contractions are noted. Aspiration is performed first to check for intravascular
penetration then local is injected in small increments to detect intraneural or intraarterial
injection. If bone is encountered without elicitation of parethesias or motor response stimulation
then needle advancement was likely to be too anterior and the needle is redirected. 2-3cc of local
is injected 1st and motor activity fade is observed in 10-15 seconds. Aspiration should be done
every 5cc of injection. After injection the syringe is removed and retrograde flow of local should
be observed for, as this is indicative of proper local anesthetic placement. Proximal pressure can
be applied to favor spread of local distally. 20-40 cc of local anesthetic is used depending on
extent of block required, patient condition, and the stature of the patient. 40cc of local does not
guarantee spread to cover ulnar nervation.
Photo obtained from Brown, Novak, & Underwood 2003 Anesthesia
Class Project PowerPoint on Interscalene Plexus Block.
Photo obtained from Brown, Novak, & Underwood 2003 Anesthesia
Class Project PowerPoint on Interscalene Plexus Block.
Block Assessment
Successful neuraxial blockade relies upon spread of the local anesthetic, therefore
adequate “soak time” of 20-30 minutes after block administration should be allowed to achieve
adequate surgical anesthesia. Care must be taken when assessing block as injuries to the arm or
body can occur if the arm is not supported and allowed to fall onto the patient or down to their
side. Motor blockade occurs before sensory block. Motor and sensory block will occur
proximally in the shoulder 1st and spreads distally. Axillary nerve motor block can be assessed
by asking the patient to abduct his upper arm against resistance. Axillary nerve sensory block can
be assessed by checking for anesthesia of the lateral aspect of the upper arm. Musculocutaneous
nerve motor block is assessed by asking the patient to flex at the elbow. Musculocutaneous nerve
sensory block is assessed by checking for anesthesia of the medial aspect of the forearm. Radial
nerve motor block can be assessed by asking the patient to extend the forearm against resistance.
Radial nerve sensory block can be assessed by checking for anesthesia of the webspace between
the thumb and first finger. Median nerve motor block can be assessed by asking the patient to
make a fist while holding extension pressure on the 1st and 2nd fingers. Median nerve sensory
block can be assessed by checking for anesthesia of the palmar surface of the thumb and 1st two
and half fingers. Ulnar nerve blockade is frequently missed by this block. Ulnar nerve motor
block can be assessed by asking the patient to abduct his “pinky” finger against pressure. Ulnar
nerve sensory block can be assessed by checking for anesthesia of the ring and “pinky” fingers.
Complications
Complications can occur due to the proximity of other anatomical structures. Blockade of
the stellate ganglion can occur with resultant Horner’s syndrome (triad of myosis, ptosis, and
anhidrosis). The phrenic nerve can be blocked with resultant dyspnea. This block is not done
bilaterally to avoid accidentally bilateral blockade of the phrenic nerves. The recurrent laryngeal
nerve can be blocked with resultant hoarseness. Accidental injection into the vertebral artery can
lead to rapid seizures and CNS toxicity. Accidental injection into the cervical epidural,
subarachnoid, or subdural space can lead to epidural anesthesia or a high spinal. Advancement of
the needle to far lateral can result in pneumothorax. Hematoma can occur from accidental
puncture of the vertebral or subclavian artery or the subclavian vein. Direct nerve injury can
occur due to needle trauma. It should be noted that most complications can be avoided by
remaining “superficial”. 1-1.5 cm should be adequate to reach the brachial plexus and illicit a
parasthesia.
References
1. Barash, Cullen, Stoelting. Clinical Anesthesia. 4th ed. Baltimore. Lippincott Williams &
Williams. 2001.
2. Brown, Novak, Underwood. Interscalene Plexus Block. 2003 Anesthesia Class Project.
3. Cousins, Bridenbaugh. Neural Blockade. 3rd ed. Philadelphia. Lippincott – Raven. 1998.
4. Morgan, Mikhail, Murray. Clinical Anesthesiology. 3rd ed. New York. Lange. 2002.
5. Reese. Upper Extremity Blocks. AANA.
Study Questions
1. What nerves come from the brachial plexus?
2. What are some complications of an Interscalene block?
Study Questions
1. What nerves come from the brachial plexus?
Axillary, Musculocutaneous, Radial, Median, & Ulnar nerves
2. What are some complications of an Interscalene block?
Dyspnea from pneumothorax or phrenic nerve blockade
Seizures or CNS toxicity from intravascular injection
Horner’s syndrome from stellate ganglion blockade
Hoarseness from recurrent laryngeal nerve blockade
High spinal from subarachnoid/subdural injection
Hematoma
Nerve injury from needle trauma