Anesthesia for Hand Surgery

Adequate anesthesia is essential in the proper evaluation and treatment of most hand injuries. The type of anesthesia required is dictated by the level and severity of injury. Prior to administering any anesthetic, a careful neuromuscular examination of the area should be performed. The integrity of the sensory nerves and muscle–tendon units in the region to be anesthetized must be determined to assure these structures are not injured. Local anesthetics should not be given directly into an area that might be infected.

Selection of Anesthetic Agent

The most commonly used local anesthetic agents are lidocaine (1% or 2%) solution and bupivacaine (0.25% or 0.5%) solution. Lidocaine is effective quickly but lasts 1.5 to 3 hours. Bupivacaine is effective over 15 to 30 minutes, but lasts 3 to 10 hours. A 50-50 solution of the two agents is effective in combining the benefits of both agents. Solutions with epinephrine should not be used in blocks around the fingers and hand because of its vasoconstrictive effect. The maximum dose of anesthetic agents is lower when given without epinephrine. The maximum dose of lidocaine is 4.5 mg/kg. For adults, the maximum total dose should not exceed 300 mg. The maximum dose of bupivacaine is 2.5 mg/kg. The maximum total dose of bupivacaine should not exceed 175 mg. The addition of 1 mL of sodium bicarbonate solution per 10 mL of anesthetic alkalinizes the solution and decreases discomfort during injection. As with any injection, it is important to aspirate before injecting to avoid an intravascular injection of the agent. Early symptoms of toxicity from an intravascular injection include headache, ringing in the ears, numbness in the tongue and mouth, twitching of facial muscles, and restlessness. As the systemic levels of the agent increase, convulsions can result, followed by respiratory arrest and arrhythmias.

Types of Blocks

Field Blocks

Direct infiltration into the wound edges is useful for many dorsal wounds and some palmar wounds where exploration of deep structures is not anticipated. It is also commonly used for procedures such as first dorsal compartment and trigger finger releases. When done with a long-acting anesthetic agent, it provides postoperative analgesia after short-acting anesthetics such as Bier blocks or general anesthesia. The technique is simple and may be converted to another type of block if insufficient. The disadvantage is that it makes the soft tissues edematous and sometimes hemorrhagic, thereby further injuring the soft tissue and distorting the anatomy.

When doing the block, a 25-gauge, 1½-in. needle is inserted at one end of wound and advanced parallel along one side of the incision. The anesthetic is injected subcutaneously until the wound edges are seen to swell. The deep spaces may be injected similarly if required.

Digital Blocks

Digital blocks are the preferred type of anesthesia for procedures done distal to the PIP joint. Caution should be used when giving digital blocks after injury to the digital artery that may require revascularization because the digital nerves and arteries run together. Digital blocks should also not be given when there is an infection around the MP joint.

A 25-gauge, 1½-in. needle is inserted distally in the web space where the skin innervation is less dense than in the palm (Fig. 1). The needle is advanced under the dorsal skin to the MP joint and 1 mL of anesthetic is injected into the subcutaneous space. The needle is withdrawn half way and directed palmarly between the MP joints. The needle is advanced until it is almost subcutaneous. Two to three milliliters are injected palmarly. The procedure is then repeated on the other side of the digit.

In the thumb, the two digital nerves are more palmar and closer together than in the digit. The ulnar digital nerve lies just palmar to the first web and the radial digital nerve lies just radial to the midline. Both nerves can be blocked by inserting the needle from ulnar to radial into the first web space at the MP joint. Two to three milliliters of anesthetic are injected transversely along the MP crease. Dorsal injections are given via sites at the radial and ulnar borders of the MP joint. Care should be taken to not give a “ring block,” or circumferential injection at the MP joint. This block may tightly compress the tissues and compromise vascularity of the digit. As with any block in the hand, no effort is made to elicit paresthesias during the injection. The needle should be withdrawn and replaced in order to avoid injection into the nerve if paresthesias are elicited.

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