Continuing Education Activity

The digital nerve block is a simple procedure that can be performed to provide immediate anesthesia for a multitude of injuries and procedures, such as fractures, dislocations, laceration repair, fingernail removal, or drainage of infections. It is one of the most commonly performed nerve blocks performed in the emergency department due to its wide variety of uses and efficacy. This activity reviews the technique of a digital nerve block, its indications, contraindications, and potential complications.

Objectives:

• Describe the indications of a digital nerve block.
• Outline the technique of performing a digital nerve block.
• Summarize the potential complications of a digital nerve block.
• Review the importance of improving care coordination among interprofessional team members for patients undergoing a digital nerve block.

Introduction

A digital nerve block is a simple procedure that can be performed to provide immediate anesthesia for a multitude of injuries and procedures, such as fractures, dislocations, laceration repair, fingernail removal, or drainage of infections. It is one of the most commonly performed nerve blocks performed in the emergency department due to its wide variety of uses and efficacy.[1] The digital nerve block is generally superior to local infiltration due to the reduced amount of anesthetic required. This is of importance as only a limited volume of anesthetic is tolerated in the restricted space of the digits.[2] It is also considered to be superior to intravenous and oral medications as it acts locally and therefore has a lower likelihood of systemic adverse effects.

Anatomy and Physiology

In order to properly perform this procedure, healthcare providers must have a thorough knowledge of the regional anatomy. Digital nerve blocks are intended to anesthetize specific nerves that originate at the wrist from the deep branches of the median, radial, and ulnar nerves. If holding the palm downward and looking down the fingertip toward the hand, there are both dorsal and palmar nerves. The dorsal set of nerves run alongside the digit at the 10- and 2-o'clock positions, while the palmar set of nerves travel at the 4- and 8-o'clock positions (see attached image). The palmar cutaneous branch of the median nerve supplies the palmar surface of digits 1-3, the palmar radial surface of digit 4, and the dorsal nailbed of these same digits to approximately the distal interphalangeal (DIP) joint. The palmar cutaneous branch of the ulnar nerve supplies the ulnar half of digit 4 on both the palmar and dorsal surfaces, as well as the entirety of digit 5. These nerves are known as the palmar digital nerves. The superficial branch of the radial nerve supplies the dorsal surface of digits 1-3 to approximately the DIP joint and the dorsal radial surface of digit 4. Anatomical knowledge of digital nerve innervations is of clinical relevance due to multiple nerves providing sensation to each finger, in some instances requiring multiple sites of anesthetic to provide adequate analgesia.[3]

Indications

Indications for digital nerve block include:

• Immediate relief of pain to the digit
• Repair of complex lacerations to the digit
• Reduction of phalangeal dislocation
• Reduction of phalangeal fracture
• Drainage of digital infections such as felon or paronychia
• Removal of the nail plate
• Ring entrapment and removal
• Foreign body removal

Contraindications

Contraindications to digital nerve block include, but are not limited to patient refusal, overlying infection at the site of injection which could result in inoculation of a deeper or intravascular infection, distortion of landmarks, or allergy to local anesthetics. Digital blocks are commonly taught to be performed without epinephrine due to the risk of vasoconstriction leading to distal necrosis. However, recent studies provide no evidence of this occurrence.[4][5]

Equipment

Required equipment for this procedure include:

• Anesthetic agent: selection depends on the intended duration of the block (see below) and the patient's reported allergies
• 27-30 gauge needle for injection
• 18-22 gauge needle for medication draw
• 5 or 10 mL syringe
• Skin cleansing agent, such as alcohol prep pads or chlorhexidine 2% 
• Access to lipid emulsion solution in case of local anesthetic systemic toxicity[6]
• Consider local diphenhydramine if the patient is allergic to both amides and esters local anesthetics

The anesthetic choice should be tailored to the length of the desired analgesia. The most commonly used anesthetics are lidocaine (1.5-2 hours), lidocaine with epinephrine (2-6 hours), bupivacaine (2-4 hours), and mepivacaine (3-5 hours).

Personnel

Digital blocks only require one provider in a cooperative patient. For uncooperative or pediatric patients, providers should consider an assistant to help stabilize.

Preparation

The patient should be educated about the procedure and informed about risks and benefits. Informed consent should be obtained before the start of the procedure. Required equipment should be brought to the bedside.

Technique or Treatment

A dorsal approach is preferred due to the thinness of the skin in this location and decreased sensitivity.[7]

The procedure is performed in the following steps:

1. Have the patient place their hand palm-down on a clean, flat, sturdy surface
2. Using aseptic technique, identify landmarks and clean area using an alcohol wipe or chlorhexidine 2%
3. Insert a 27 gauge needle according to the nerve block desired. The dorsal and palmar nerves on each side can be anesthetized with a single needle puncture.[8][9]
   1. For superficial dorsal nerves - perpendicular to the digit into the dorsal aspect of the web space on one side of the digit slightly distal to the knuckle
   2. For superficial palmar nerves - perpendicular to the digit into the palmar aspect of the web space on one side of the digit slightly distal to the knuckle, taking care not to advance through the palmar skin
4. Advance the needle slightly
5. Aspirate to ensure the needle is not intravascular, then inject 0.5 to 1.5 mL of the local anesthetic solution while withdrawing the needle
6. Firm massage for approximately 30 seconds to enhance the diffusion of the anesthetic
7. Repeat the procedure on the opposite side of the digit to be blocked

Complications

Complications of digital nerve blocks include, but are not limited to infection, bleeding, increased pain, vascular injection of anesthetic, nerve injury including neuropraxia or neurolysis, local anesthetic systemic toxicity (LAST), and allergic reaction.

Clinical Significance

Clinicians have a multitude of ways to provide anesthesia to patients in pain so they may perform maneuvers or procedures effectively while allowing for minimal discomfort to the patient. Anesthesia may be approached in a multimodal manner as there are multiple areas that one may target the transmission of pain as it propagates from the site of injury to the cerebral cortex. One such modality of pain relief is by targeting the peripheral nerve, which serves to transmit pain signaling from tissues. The tissue in which the injury occurred may be targeted by anesthetics to limit the transduction of pain as can the peripheral nerves which innervate the tissue and serve to transmit pain signals to the cerebral cortex.[10]

Targeting the transduction of pain from the level of the tissue may be accomplished by the use of drugs that impede the pain signaling pathway, for example, opioids, nonsteroidal anti-inflammatory drugs (NSAIDs), or local infiltration of the injured tissue with an anesthetic. A disadvantage of using local infiltration is that the anesthetic is injected directly and/or indirectly into tissues and distorts the anatomy that the clinician needs to visualize to perform repairs. This technique is also associated with decreased patient comfort due to the amount of pain experienced during this procedure as a large amount of anesthetic is required for therapeutic effect.

The peripheral nerve may also be targeted by systemic analgesic agents such as opioids, tricyclic antidepressants (TCAs), or other dissociative drugs, but the nerve may also be directly targeted by the use of anesthetic agents in a technique known as a nerve block. Nerve blocks may be utilized proximal to the area of injury to provide a larger region of anesthesia, or they may be used regionally for targeted anesthesia closer to the injured tissue. A regional nerve block, and in particular the digital nerve block, is one such technique that allows for targeted anesthesia and is typically tolerated better by patients than local wound infiltration and allows for a large area of anesthesia in relation to the amount of anesthetic required.[11]

The digital nerve block can be considered for use in the repair of various injuries such as repair of a complex laceration to a digit, reduction of phalangeal dislocation or fracture, drainage of digital infections such as felon or paronychia, the removal of the nail plate, or for ring entrapment and removal. Once a clinician becomes familiar with the anatomy and technique of this procedure, then it may be utilized extensively in practice.

Enhancing Healthcare Team Outcomes

The digital nerve block procedure is one that requires an interprofessional team of professionals in the healthcare field which includes: clinicians, nursing staff, and a pharmacist. It is critical for these patients to receive a full history and physical before the procedure including a history of adverse drug reactions. In particular, this will include a history of local anesthetic use to identify alternatives, if required. A team-based approach to this procedure will limit deleterious events and should include the following before the start of the procedure: assessment of adverse events to local anesthetics and availability of alternative agents, calculation of maximum weight-based dosage of local anesthetic, consult with the pharmacist about the availability of a lipid emulsifying agent in the event of LAST, monitoring the patient for signs and symptoms of LAST such as altered mental status (AMS), metallic taste, seizures, respiratory distress, tachycardia, dysrhythmia, atrioventricular (AV) block, or cardiovascular collapse [Level 3], and availability of ACLS trained staff in the event of cardiovascular symptoms.[12]