Interscalene Block: Nerve Block for Shoulder Surgery
Interscalene Brachial Plexus Block
Interscalene blocks are used to relieve pain during and after surgery on the shoulder. The interscalene block is included in the category of regional anesthesia and is one of the most commonly used types of peripheral nerve blocks. First, the relevant definitions to make it easier to follow the medical-speak.
- Regional anesthesia: refers to the technique of numbing a large area of the body by injecting numbing medicine (local anesthetic) around a nerve or group of nerves that supplies that area of the body. Sometimes epidurals and spinals are included in the category as they numb the lower half of the body.
- Peripheral nerve block: essentially the same as regional anesthesia, but specifically excludes epidurals and spinals. 'Peripheral' refers to nerves outside of the central axis of the nervous system (brain and spinal column).
- Interscalene block: numbing the nerves that supply the shoulder by injection of local anesthetic around the base of those nerves in the side of the neck.
Xray of Cervical Vertebrae
Brachial Plexus Anatomy- The Basics
The brachial plexus is a complex conglomeration of nerves in the upper neck and shoulder area. Nerve endings leave the upper spinal cord, join together, branch apart, divide, and eventually spread out into the individual nerves that travel out to provide sensation and movement to the shoulder and arm.
The vertebrae (backbones) -- and the nerves that exit the spinal cord near them -- are grouped by location:
- seven cervical at the top of the neck (designated C1 to C7)
- twelve thoracic from the top to the low back (T1 to T12)
- 5 lumbar in the low back (L1 to L5)
- then the sacrum and coccyx at the level of the hips and tailbone
The nerves at the origin of the brachial plexus come from the cervical spine, at levels C5, C6, C7 and the first thoracic vertebrae, T1.
A review of the detailed and complex anatomy of the brachial plexus is well beyond the scope of this article. As a quick summary, those cervical and thoracic nerves combine to form nerve trunks, the trunks become divisions with some of the original nerve fibers staying together and some splitting up. Then again, the divisions become cords and then branches which become the peripheral nerves providing sensation and movement to the arms.
Diagram of the Brachial Plexus
The key to understanding how to perform an interscalene block and what to expect from it lies in this complicated anatomy. Injection of the numbing medicine must occur at a place that is accessible and effective for the purpose intended.
Your anesthesiologist has been trained in this technique. The injection will be done with either the nerve stimulator technique or with ultrasound guidance. Either way, you will likely be lightly sedated for the procedure and may or not remember parts of it later.
As with other peripheral nerve blocks, patients say it "feels funny" when the nerve stimulator is used (makes the muscles twitch), but I've not had anyone say that it hurts to have it done.
Remember, that the duration of action of the interscalene block is about 8 to 24 hours with the average being maybe 10 to 12 hours. The interscalene block will not eliminate the need for pain pills (or intravenous medicine if you stay in the hospital). It will decrease the amount you need the first day and delay the hour at which you start taking them. This can be helpful to reduce pain during the drive home from the hospital, but you will likely still need pain meds that evening, night or early the next morning.
Interscalene Block Technique
As stated, the block is done either with a nerve stimulator or by ultrasound guidance. Either way, you will likely receive some sedation and be placed on monitor for your EKG, blood pressure and oxygen levels to be measured. The neck will be cleaned with antiseptic soap and you will be asked to turn your head away from the side getting the block. You may be asked to lift your head or tense your neck muscles briefly to help identify the muscular landmarks used to do the block.
The big muscle running down and diagonally toward the front of your neck is the sternocleidomastoid. Behind this are the scalene muscles. There is a groove between the anterior and middle scalene muscles. This is the interscalene groove, and is the site of injection for this block.
Local anesthetic is usually given to numb the skin where the injection will go. The needle is passed just a centimeter and no more than two into the correct spot on the side of the neck. If a nerve stimulator is used, your arm will start to twitch, but will stop in a few seconds after the anesthesiologist starts to inject the numbing medicine.
What To Expect from an Interscalene Block
- Numb shoulder
- Some arm numbness- be careful around hot or cold items, you may not feel burn or damage from temperature extremes
- Heavy weak arm that may be difficult to lift up and away from the body
- Usually 8 to 24 hours of pain relief (average may be around 12 with currently used medications)
- Maybe Horner's syndrome
- Maybe some feelings of shortness of breath
Interscalene Block Effects
When the brachial plexus is blocked by the interscalene technique, it can be expected to provide anesthesia or analgesia to the shoulder joint and overlying structures.
This block is performed at the level of C6, which is approximately the level just below the Adam's apple in the neck. The block numbs those parts of the shoulder innervated by the nerves originating from C5 to C7.
Functionally, this results in reliable numbing of the shoulder area. Some parts of the upper and lower arm will be numb, but the hand will not. For this reason, interscalene blocks are only recommended for shoulder surgery. It will be difficult to raise the arm from the shoulder as the arm will feel heavy and weak.
Interscalene Block Side Effects
A side effect that may be expected (but may or may not occur) is Horner's syndrome. This is a condition caused by the blockade of sympathetic (part of the autonomic nervous system) nerve fibers involved in the interscalene block. I find this occurs in less than one in ten patients receiving an interscalene block. It is not considered a complication and is a normal variant of the block. It will resolve as the interscalene block wears off.
The resulting symptoms occur on the same side as the block and include:
- Ptosis: This is drooping of the eyelid
- Miosis: Constriction (making smaller) of the pupil
- Anhidrosis: Lack of sweating
The diaphragm (breathing muscle under the lungs) is innervated by the phrenic nerve. The phrenic nerve is supplied by C3, C4 and C5 nerve roots. Therefore, the phrenic nerve and the breathing muscle on the side of the block are paralyzed by an interscalene nerve block. This sounds really bad and dangerous, but unless you have severe lung disease, it usually doesn't create a problem. This nerve is blocked 100 percent of the time when a successful block is placed.
You should know that you may or may not notice a strange feeling of not being able to take a deep breath until the block wears off. Your cough may or may not feel weak. Most people do just fine, with the other side of the diaphragm functioning normally. Oxygen level is not usually affected and this is of no clinical consequence in most people.
Hoarse Voice and Difficulty Swallowing
Because one of the nerves to the larynx (the recurrent laryngeal nerve) may be blocked by normal spread of the local anesthetic, a temporary hoarse voice may also result. Like the above side effects, this is not a complication or a problem, just a normal variant of the block that happens sometimes. Difficulty swallowing may or may not accompany this side effect.
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Interscalene Block Complications
Anytime an injection or medicine is given, there are potential complications. This is to be expected since the purpose of the intervention is to change something about how the body works. An interscalene block is no exception.
Complications can occur as a result of the medication, the needle used or both. These may be more likely in people with certain pre-existing conditions.
The neck has a dense concentration of structures that are important structures. The brachial plexus is only one of them. Other nerves, the carotid artery, the jugular veins, the spinal column, the epidural space, the windpipe… These are all structures near the injection site for interscalene block. Obviously, injection into one of these structures can be catastrophic.
Injections always have a risk of infection or bleeding. Because the blood vessels in the neck are large and important, causing injury to one is potentially dangerous. Luckily, this complication is rare.
If local anesthesia is injected into blood vessels, seizures, cardiac collapse and even death can occur. This also, is very rare.
Drops in blood pressure and heart rate have been reported due to reflexes that affect the part of the nervous system that controls these functions.
Injury to nerves, with or without warning during the procedure, can occur. In other words, some people have reported either temporary or permanent nerve injury after getting a seemingly perfectly performed interscalene block. Most of the time, if numbness or tingling persist after the block has worn off, it will resolve itself over, at most, a few months. Rarely, the nerve damage can be severe or permanent.
It is difficult to find reliable data on the exact percentages of these occurrences, due to differences in reporting or accurate identification of the problem. The risk of any complication from interscalene block has been estimated to be anywhere from 5 to 20 percent. The more serious the complication, the more rare it is.
If you are having shoulder surgery, talk to your surgeon and anesthesiologist about your particular needs and risks, as there is a lot of variability from case to case.
Personally, this author uses them for total shoulder replacement and open rotator cuff repairs, most of the time and quite rarely for any arthroscopic surgery (through the scope) on the shoulder. I work with some surgeons who believe the risk is too high and request that their patients never have them, and some surgeons who request most of their patients get them.