Chapter 18 Carpal Tunnel Decompression of the Median Nerve
ADVANTAGES OF WALANT VERSUS SEDATION AND TOURNIQUET IN CARPAL TUNNEL DECOMPRESSION
When you perform wide awake hand surgery, you do not have to deal with your patient′s medical comorbidities, which would only be a problem if the patient has been sedated. It is safer for your patients to have no sedation. They just get up and go home after surgery, like when they have had a filling at the dentist.
A major advantage of eliminating sedation for carpal tunnel surgery is that you do not need to perform the procedures in the main operating room. You can do all of your carpal tunnel surgeries in minor treatment rooms in the clinic outside the main operating room with evidence-based field sterility (see Chapter 10).
You can easily perform 15 or more carpal tunnel releases in 1 day with only one nurse using field sterility in the office or clinic. You can also see consultation and recheck patients between operations (see Chapter 14).
You avoid tourniquet let-down bleeding.
You do not need to use a cautery, particularly if you inject the epinephrine 30 minutes before the first incision. We have not opened a cautery for over 25 years for carpal tunnel release. Hematoma has not been a problem, even in patients on anticoagulants.
Your patient remains pain free with the median and ulnar nerve block for up to 5 hours using the technique described below.1 Nausea and vomiting do not occur, because you have given the patient no perioperative narcotic agents.
Although patients can “tolerate” 7 minutes of tourniquet control, they will not experience any tourniquet pain at all if you simply use epinephrine with the lidocaine. There is high-level published evidence that the tourniquet hurts twice as much as the injection of a local anesthetic in carpal tunnel surgery.2,3 Patients appreciate the tourniquet-free experience.
Dr. Kerrigan notes: “For years I used to do endoscopic carpal tunnel releases with a local anesthetic and with an upper arm tourniquet. I would often ask patients what bothered them the most, if anything, at the end of the procedure. The most common response I got was that the tourniquet was uncomfortable. Now (since I switched to the WALANT technique) when I ask the question, the most common response I get is, ‘It really wasn′t bad at all, not even as bad as going to the dentist.’”
All of the general advantages listed in Chapter 2 apply to both the surgeon and the patient.
WHERE TO INJECT THE LOCAL ANESTHETIC FOR AN OPEN CARPAL TUNNEL RELEASE
See Chapter 1, Atlas, for more illustrations of the anatomy of diffusion of tumescent local anesthetic in the forearm, wrist, and hand.
SPECIFICS OF MINIMALLY PAINFUL INJECTION OF LOCAL ANESTHETIC IN OPEN CARPAL TUNNEL RELEASE
We inject the anesthetic solution a minimum of 30 minutes before surgery to allow the epinephrine to take optimal effect and provide an adequately dry working field.4
We inject supine patients on stretchers in a waiting area to decrease the risk of their fainting (see Chapter 6).
To minimize the pain of injection, use a fine 27-gauge needle (not a 25-gauge) into the most proximal red dot injection point.
Ask the patient to look away. Press with a fingertip just proximal to the injection site before you put in the needle to add the sensory “noise” of touch and pressure to decrease the pain.
Insert the first needle perpendicularly into the subcutaneous fat. Stabilize the syringe with two hands and have your thumb ready on the plunger to avoid the pain from needle wobble until the skin needle site is numb. Inject the first visible 0.5 ml bleb and then pause. Ask the patient to tell you when the needle pain is all gone. After he tells you the pain is gone, inject the rest of the first 10 ml slowly (over 2 minutes) without moving the needle.
Ask the patient to tell you if he or she feels further episodes of pain during the injection so you can score your injection technique, as outlined in Chapter 5. If the patient feels pain twice, you score an eagle, three times a birdie, four times a bogie, and so on. It takes 5 minutes to perform the injection for a carpal tunnel release and consistently get a hole-in-one, where the patient feels only the stick of the first 27-gauge needle in the injection process.5–7
Inject 10 ml of buffered 1% lidocaine with 1:100,000 epinephrine just ulnar to the palmaris longus at the proximal injection point, as shown in the figure on p. 130. This should be near the median nerve, but never in the nerve. Do not elicit paresthesias (electric shock feeling).
The first 2 ml is injected just subcutaneous in the fat. Notice the location of small subcutaneous veins and avoid them.
Advance slowly and more deeply to get under superficial fascia of the forearm to inject the remaining 8 ml for the median nerve block. This will also numb the ulnar nerve. If you are not under the forearm fascia, you may not block the nerve.
After the initial 10 ml, come back to the subcutaneous plane with the needle tip and slowly infiltrate 10 ml from proximal to distal in an antegrade direction down the palm between the skin and the superficial palmar fascia. Blow the local anesthetic slowly ahead of the needle so there is always at least 1 cm of visible or palpable local anesthetic ahead of the sharp needle tip that the patient would feel if you advanced it into “live” nerves. Follow the rule of “Blow slow before you go.” (See Chapter 5 for further tips on how to inject local anesthetic with minimal pain.)
When reinserting the needle, do so into skin that is within 1 cm of clearly vasoconstricted white skin that has functioning lidocaine and epinephrine so the needle reinsertion is pain free.
To avoid all pain in suturing the wound, be sure to have visible or palpable local anesthetic at least 1 cm on either side and 1 cm past the distal end of the palmar incision.
You can also inject with a blunt-tipped cannula to increase the speed of painless injection compared with sharp needle tip injection (Clip 18-3 shows this blunt-tipped cannula injection for carpal tunnel surgery; also see Chapter 5). The blunt needle tip can push quickly with no pain past “live” unanesthetized nerves by gliding in the fat. Sharp needle tips will pierce nerves and cause pain if the local anesthetic is not bathing the nerve well ahead of the needle tip and if the operator is not moving slowly enough to let the local anesthetic work before the needle tip reaches the nerves. For this operation, insert a 37 mm long 27-gauge cannula into a needle hole created in numbed skin with a 25-gauge needle.
Previous publications have documented the use of 10 ml for the median/ulnar nerve block and then another 10 ml in the palm.6–8 Some surgeons think that 10 ml is an unnecessarily large volume for the median nerve block. Dalhousie New Brunswick medical students have recently performed a level I evidence study in which volunteers had bilateral median nerve blocks with 5 ml on one side and 10 ml on the other side. There were clearly more median nerve block failures in the 5 ml group than the 10 ml group (to be published).
In some patients, the forearm fascia acts as a barrier to local anesthesia diffusion. If you only inject subcutaneously in the wrist, and do not have the needle under the forearm fascia, you may not get a median nerve block as the local may not penetrate the forearm fascia.
Some people only inject under the skin with no intention of getting a median nerve block, and routinely successfully do carpal tunnel surgery under local this way. This works well. However, a possible disadvantage of this approach is that patients sometimes feel “electric jolts” when the live nerve is stimulated during the surgery.
When you perform wide awake carpal and cubital (see Chapter 19) or lacertus tunnel (see Chapter 20) releases at the same time, simply decrease the concentration of the local anesthetic to 0.5% lidocaine with 1:200,000 epinephrine. For a cubital tunnel release, inject 60 ml at the elbow, as described in Chapter 19, and 20 ml in the hand for the carpal tunnel. For a lacertus tunnel release, inject 30 ml over the median nerve at the elbow, as described in Chapter 20, and 20 ml in the carpal tunnel.