Digital Nerve Block

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A digital block is the technique of blocking the nerves of the digits to achieve anesthesia of the finger(s). This technique is simple to perform and essentially devoid of systemic complications. It is a commonly used and effective method of anesthesia for a wide variety of minor surgical procedures on the digits.

Overview

 Indications: arm, elbow, forearm, and hand surgery

 Transducer position: approximately parasagittal, just medial to coracoid     process, inferior to clavicle

 Goal: local anesthetic spread around axillary artery

 Local anesthetic: 20-30 mL


 

General Considerations

A digital block is the technique of blocking the nerves of the digits to achieve anesthesia of the finger(s). This technique is simple to perform and essentially devoid of systemic complications. It is a commonly used and effective method of anesthesia for a wide variety of minor surgical procedures on the digits. As such, this block should be in the armamentarium of every anesthesiologist. Several different techniques of digital block and their modifications are available, in this chapter, we chose to describe the one that is most commonly used in our institution. The figure shows a patient with avulsion of the middle finger, a typical indication for the use of the digital block.


Regional Anesthesia Anatomy




The common digital nerves are derived from the median and ulnar nerves and divide in the distal palm into the volar aspect, tip, and nail bed area.



The main digital nerves, accompanied by digital vessels, run on the ventrolateral aspect of the finger immediately lateral to the flexor tendon sheath. Small dorsal digital nerves run on the dorsolateral aspect of the finger and supply innervation to the back of the fingers as far as the proximal joint.

Patient Positioning

                            The hand is pronated and rested on a flat surface or supported by an attendant.

Equipment




A standard regional anesthesia tray is prepared with the following equipment:

 Sterile towels and 4"x4" gauze packs

 A 10-mL syringe with local anesthetic

 One 1½" 25-gauge needle

Technique

 

Block of Volar and Dorsal Digital Nerves at the Base of the Finger

A 25-gauge 1½" needle is inserted at a point on the dorsolateral aspect of the base of the finger and a small skin wheel is raised. The needle is then directed anteriorly toward the base of the phalanx. The needle is advanced until the it contacts the phalanx, while the anesthesiologist observes for any protrusion from the palmar dermis directly opposite the needle path. One mL of solution is injected as the needle is withdrawn 1 to 2 mm from the bone contact. An additional 1 mL is injected continuously as the needle is withdrawn back to the skin. The same procedure is repeated on each side of the base of the finger to achieve anesthesia of the entire finger.

Transthecal Digital Block

The transthecal digital block is placed by using the flexor tendon sheath for local anesthetic infusion. In this technique, with the patient's hand supinated, the flexor tendon is located. Using a 25 to 27 gauge 1-inch needle, 2 mL of local anesthetic is injected into the flexor tendon sheath at the level of the distal palmar crease. The needle should puncture the skin at a 45-degree angle. Resistance to the injection suggests that the needle tip is against the flexor tendon. Careful withdrawal of the needle results in the free flow of medication as the potential space between tendon and sheath is entered. Proximal pressure is then applied to the volar surface for the duration of the injection for the diffusion of the medication throughout the synovial sheath.



TIPS:

 The advantage of this approach is the provision of anesthesia to the entire digit with a single injection and a reportedly     a higher success rate.

 For more extensive surgery on the finger, it may be advantageous to combine both approaches discussed in this chapter     for a greater success rate and more extensive distribution of anesthesia.


Choice of Local Anesthetic

The choice of the type and concentration of local anesthetic for a digital block is based on the desired duration of blockade. Below, the onset times and duration of anesthesia for some commonly used local anesthetics mixtures.

Local Anesthetic

Onset (min)

Anesthesia (hrs)

Analgesia (hrs)

1.5% Mepivacaine (+ HCO3)

15-20

2-3

3-5

2% Lidocaine (+ HCO3)

10-20

2-5

3-8

0.5% Ropivacaine

15-30

4-8

5-12

0.75% Ropivacaine

10-15

5-10

6-24

0.5 Bupivacaine (or I-bupivacaine)

15-30

5-15

6-30

Block Dynamics and Perioperative Management

A skin wheel at the point of needle insertion significantly reduces the discomfort during the placement of the block. A digital block requires a small dose of a sedative or a narcotic during placement. Typical onset time for this block is 10-20 minutes, depending on the concentration and volume of local anesthetic used.

Complications and How to Avoid Them

The choice of the type and concentration of local anesthetic for a digital block is based on the desired duration of blockade. The onset times and duration of anesthesia for some commonly used local anesthetics mixtures.

Infection

 This should be very rare with use of an aseptic technique.

Hematoma

 Avoid multiple needle insertions.

 Use 25-gauge needle (or smaller) and avoid puncturing superficial veins.

Vascular Puncture

 Avoid puncturing the greater saphenous vein at the medial malleolus

 Intermittent aspiration should be performed to avoid intravascular injection

Other

Instruct the patient to the care of the insensate finger

Gangrene of the digit(s)

 Avoid epinephrine-containing solution for this block

 Limit the injection volume to 2mL on each side

 The mechanical pressure effects of injecting solution into a potentially confined space     should always be borne in mind, particularly in blocks at the base of the digit

 In patients with small vessel disease, perhaps an alternative method should be     sought in addition to avoidance of digital tourniquet

Nerve Injury

 Residual paresthesias are likely due to an inadvertent intraneuronal injection

 Systemic toxicity is rare because of the distal location of the blockade

 Do not inject when the patient complains of pain or when high pressures on injection     are met

Bibliography

1.

Brown DL, Bridenbaugh LD: The Upper Extremity. Somatic Block . In Cousins, M.J., and Bridenbaugh PO (eds): Neuronal Blockade in Clinical Anesthesia and Management of Pain. Philadelphia, J.B. Lippincott-Raven Publishers,1988,pp345-71.

2.

Chiu DTW: Transthecal digital block: flexor tendon sheath used for anesthetic infusion. J Hand Surg 1990; 15: 471-3.

3.

Flarity-Reed K: Methods of digital block. J Emerg Nurs 2002; 28:351.

4.

Freedman RR, Mayes MD, Sabharwal SC: Digital nerve blockade in Raynaud's disease. Circulation 1989; 80:1923.

5.

Kirchhoff R, Jensen PB, Nielsen NS, Boeckstyns ME: Repeated digital nerve block for pain control after tenolysis. Scand J Plast Reconstr Surg Hand Surg 2000; 34:257.

6.

Morrison WG: Transthecal digital block. Arch Emergency Medicine 1993; 10:35-8.

7.

O'Donnell J, Wilson K, Leonard PA: An avoidable complication of digital nerve block. Emerg Med J 2001; 18:316.

8.

Sarhadi NS, Shaw-Dunn J: Transthecal digital nerve block. An anatomical appraisal. J Hand Surg [Br] 1998; 23:490.

9.

Torok PJ, Flinn SD, Shin AY: Transthecal digital block at the proximal phalanx. J Hand Surg 2001; 26:69.

10.

Wilhelmi BJ, Blackwell SJ, Miller JH, Mancoll JS, Dardano T, Tran A, Phillips LG: Do not use epinephrine in digital blocks: myth or truth? Plast Reconstr Surg 2001; 107:393.

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