To the Editor:—
I wish to thank Dr. Benumof for his interesting but tragic report of four patients in the December 2000 issue of Anesthesiology. 1However, I would like to object to his choice of title, “Permanent Loss of Cervical Spinal Cord Function Associated with Interscalene Block Performed under General Anesthesia.” The procedures performed were obviously not interscalene blocks but rather attempted blocks because the anesthetic solution was not placed in the interscalene sheath.
Winnie 2states that the fascia of the anterior and middle scalene muscles “serves as a sheath of the plexus.” He further comments that the needle is to be advanced slowly and that “a very short distance under the skin the fascia is penetrated.”
I have performed more than 500 interscalene blocks, and most have been continuous blocks. The blocks were performed in awake and unmedicated patients. The plexus is extremely superficial and is the basis for the karate chop to the neck, thereby temporarily immobilizing the upper arm. I have measured the skin to interscalene sheath distance in the average adult and found that it is 0.7–1.5 cm. In very obese patients (300–400 lb), the distance is no more than 2.5 cm. The use of a nerve stimulator may give a false feeling that one is within the sheath. An incomplete block, failed blocks, or increased risk of phrenic or recurrent laryngeal paralysis may result. 2“Walking” the needle at the C6 transverse process, as has been described, 2is not recommended because the needle depth would be greater than 1.5 cm in the average adult. Performing this block during general anesthesia is difficult because the tissues are relaxed, and feeling the “pop” into the sheath would be missed. Further, the elicitation of a paresthesia cannot be achieved. This paresthesia is normally described as a vague sensation in the shoulder, anterior chest wall, or down the arm and is easily and comfortably found. This is an extremely useful block and can give the patient a pain-free intraoperative and postoperative course.
Attempting interscalene blocks during general anesthesia, as Dr. Benumof stated, is contraindicated and, if the anesthetic solution is not placed within the sheath, may lead to disaster.