For distal digital analgesia (used for surgical or diagnostic procedures), the dorsal site is located on the dorsal axis proximal to the interdigital space close to the metacarpal or metatarsal phalangeal joint. The needle should be placed with care (because the proper digital artery can be found at the dorsal site), and 10 mL of 2% lidocaine injected. If the needle is inserted deep into the interdigital space, the nerves of the flexor surface can be reached. This obviates the necessity of a flexor site block for simple procedures. The distribution of the nerve supply to the axial face of the digits of the forelimb is not constant, which makes this technique unreliable for digital analgesia of the forelimb.
The preferred flexor site is a little lower than the dorsal site because it is difficult to pass a needle through the partially cartilaginous palmar/plantar ligament. The medial and lateral sites are located at the level of the dewclaws, and the needle is inserted dorsally (horizontal in the standing animal) from a point 2.5 cm slightly proximal to the dewclaws. For the flexor site and the medial and lateral sites, ~5–8 mL of 2% lidocaine is injected. For surgery of the digit (eg, amputation), the dorsal, palmar/plantar, and medial or lateral sites are used, depending on the claw. For interdigital surgery (eg, removal of corns), both the dorsal and palmar/plantar sites are used. Differential diagnosis can be aided by selective anesthesia of the nerves of the digit.
The diagrams on this page illustrate the sites for four regional nerve blocks in the front and hind feet. The site selected should be perfused with 10 mL of 2% lidocaine using an 18–20 gauge needle.
Intravenous regional analgesia is frequently used for lengthy surgical procedures such as arthrodesis. Sedation and restraint is advised. A tourniquet is applied just below the hock or knee, the hair is clipped, and the skin sterilized from a site over a vein. Lidocaine (10–30 mL) without epinephrine is injected to produce analgesia within ~10 min. The tourniquet should never be kept in place for >60 min. When surgery is complete, the tourniquet should be loosened gradually to prevent a flood of anesthetic suddenly entering the general circulation. Concurrent injection of antibiotic may be helpful.