If you have a swollen, big foot on a bull and you can’t find a vein to administer anesthetics for procedural pain, try an interdigital block, says Meredyth Jones, DVM, MS, Dipl. ACVIM, Kansas State University.
To block a foot where swelling is so extensive that a superficial vein cannot be found, you can take about an 18-gauge 2-3-inch or longer needle and insert into the dorsum of the foot, with the insertion point about ¾ to 1 inch above the level of the coronary band, directed toward the palmar or plantar aspect of the foot.
This needle will be in the interdigital space between the 2nd phalangeal bones. If selective anesthesia of one digit is preferred over the other, the needle can be directed so that it grazes the axial surface of the 2nd phalanx on that digit. “The needle is inserted until it is at least halfway to the palmar/plantar aspect of the foot and 15 mL of lidocaine is injected into the soft tissues as the needle is withdrawn,” Jones says. Then, the procedure is repeated from the palmar/plantar aspect between and dorsal to the heel bulbs, so that the inderdigital space is flooded with lidocaine.
“The most common causes of severely swollen feet are septic arthritis of the distal interphalangeal joint and cellulitis,” Jones explains. “So, this block would be useful for claw amputation, treatment of a severe wound or drilling out and debriding the joint.”
To make finding the vein easier, apply a tourniquet. Jones uses innertubing cut into 2-inch wide strips, about 2 feet long. “They make great tourniquets for either regional anesthesia of lidocaine (Bier block) or for regional intravenous perfusion of antimicrobials,” she says.
The tourniquet is placed mid-cancannon bone and this allows injection into superficial veins of the foot. When regional anesthesia is performed in this way, it causes total anesthesia of the entire foot distal to the tourniquet, which allows aggressive debridement of a sole abscess, amputation of a claw, facilitated ankylosis or other procedures which would otherwise be very painful.
Jones says that lidocaine blocks, in general, have an onset of time of about five minutes and a duration of about 60-90 minutes. “When performing these blocks intravenously with a tourniquet, the anesthesia will last for the duration of the tourniquet, and I recommend limiting tourniquet time to about 30 minutes,” Jones suggests.