Orthopedic procedures in the arm may be performed under a variety of brachial plexus blocks, with intravenous regional anesthesia, or by using combinations of individual nerve blocks in the arm. The selection of a particular technique depends on the need for a tourniquet and on the site of anticipated surgery.
The deep structures of the shoulder are largely innervated by the C5 and C6 dermatomes. This is why shoulder surgery can be done under an interscalene block alone. Skin infiltration may be necessary to anesthetize the contribution of the intercostobrachial nerve for the posterior portal for shoulder or if the skin incision extends toward the axilla.
Side Effects of the Beach Chair Position
Open shoulder surgery or arthroscopy performed in the sitting position under interscalene block may be complicated by episodes of bradycardia or hypotension, or both, which occurs in up to 20% of cases. These are believed to be vasovagal reactions that are best prevented by fluid loading and pretreatment with intravenous atropine or beta-blockers.
It has been postulated that this vasovagal reaction is related to venous pooling (caused by the sitting position and epinephrine-induced beta-adrenergic effect) and increased inotropy (also beta-adrenergic effects of epinephrine). Increased epinephrine may occur endogenously from decreased venous return and carotid baroreceptor stimulation, as well as exogenously from epinephrine administered with the local anesthetic for interscalene block, direct wound infiltration, and the irrigation solution. These conditions are similar to those incurred during tilt-table testing in patients with unexplained syncope. Exogenous epinephrine may play a role similar to isoproterenol infusions in tilt testing, which has been shown to increase the frequency with which vasovagal reactions are induced. In this setting, syncope is preceded by a low-volume hypercontractible ventricle, and there is increased sympathetic tone. This causes stimulation of intramyocardial mechanoreceptors C fibers, which is followed by an abrupt withdrawal of sympathetic outflow with vasodilation and an increase in vagal tone with resultant bradycardia, hypotension.
Prophylactic use of beta-blockers has been compared with prophylactic glycopyrrolate administration. Prophylactic beta-blockade, but not prophylactic glycopyrrolate, reduced the frequency of hypotensive bradycardic events. Regardless of the choice to use hydration or pharmacologic prophylaxis, the anesthesiologist must be extremely vigilant and intervene early to prevent progression to asystole. Treatment may include use of ephedrine, atropine, and glycopyrrolate and positioning the patient supine until stable.
Elbow surgery can be performed by interscalene or axillary blocks or by a combination of both. Alkalinization of local anesthetics has been shown to more effectively anesthetize the C8-T1 dermatomes during interscalene blocks. Intercostobrachial blocks (T1-2) in the axilla may be necessary as a supplement to axillary blocks if medial incisions are performed in the upper arm. Hand and forearm surgery can be performed with the use of any of the previous techniques. Axillary blocks may be preferable for surgery of the medial aspect of the hand and forearm (C7-8, T1) because this area is sometimes incompletely blocked by the interscalene approach. The coracoid block is also effective for surgery of the elbow, forearm, or hand. This infraclavicular block has prominent bony landmarks, making it easier to perform with less likelihood of pneumothorax compared with other infraclavicular approaches to the brachial plexus. The site is also ideal for securing a catheter to the anterior chest wall. Continuous axillary blocks may also be used for prolonged cases. Intravenous regional anesthesia is most applicable for shorter cases.
Peripheral nerve blocks at the wrist or hand can be performed with a long-acting anesthetic such as bupivacaine or ropivacaine to provide postoperative pain relief and facilitate discharge after ambulatory surgery.
Regional anesthesia: Brachial plexus