Introduction

Digital nerve blocks are important tools for the emergency medicine clinician. Injuries or infections of the digits are extremely common. Adequate analgesia is essential to properly address the presenting condition and to minimize the patient's discomfort. Digital blocks are useful in many scenarios in which local infiltration of an anesthetic would require several injections into the already painful site of injury. Furthermore, local infiltration around the wound may create increased swelling, making the repair more difficult. Several techniques are available for performing digital blocks.

Relevant anatomy

Each digit is innervated by 4 digital nerves. In the upper extremity, the digital nerves arise from the median, ulnar, and radial nerves. The 2 palmar digital nerves innervate the palmar aspect of the digit and the nail bed, whereas the dorsal nerves innervate the dorsum of the digit (see images below). The tibial and peroneal nerves branch off into the digital nerves of the lower extremities, which follow a pattern of distribution analogous to those of the upper extremity.

Indications

Digital blocks are indicated for any minor surgery or procedure of the digits. These include, but are not limited to, the following:

• Large irregular lacerations
• Lacerations involving the nail or the nail bed
• Ingrown nails
• Felon or paronychia
• Trephination of subungual hematoma
• Digit dislocations or fractures

Contraindications

• Compromised digit circulation
• Infected injection site
• Known allergy to anesthetic

Anesthesia

Local anesthetic agents have the basic structure of an aromatic and a hydrophilic, separated in the middle by an amino-ester or an amino-amide. This forms the basis of classification of local anesthetics into 2 groups: the ester-type agents (eg, procaine) and the amide-type agents (eg, lidocaine).

The choice of agent is based on the desired duration of analgesia and the patient’s allergy profile. Lidocaine is the most commonly used anesthetic. If longer anesthesia is required, another amide anesthetic, such as bupivacaine, can be used. If the patient is known to be allergic to lidocaine, an ester-type anesthetic, such as procaine, can be substituted. Table 1 summarizes the properties of commonly used agents.

Table 1. Commonly Used Local Anesthetics and Their Properties

*Administer by small incremental doses.

Local anesthetics are to be used without epinephrine in the digits to avoid vasoconstriction of adjacent arteries, which may lead to ischemia or infarction of local tissues. Despite studies that have shown epinephrine to be safe in these circumstances, epinephrine is traditionally avoided in the digits. The block should be performed cautiously in areas where nerve function is compromised. Small volumes of anesthetic should be used to minimize local swelling, especially in cases in which compartment syndrome is being considered.

Equipment

• Sterile gloves, drapes, and gauze pads
• Povidone-iodine (Betadine) solution
• Syringe, 5-10 mL, with an 18-gauge needle for drawing up the anesthetic and a 25- to 30-gauge needle for injection
• Local anesthetic of choice

Positioning

Depending on the technique used, the extremity position varies. See the Technique section below for detailed explanations.