Surgery of the foot
In general, intravenous regional anesthesia is preferred for surgery of the foot. A tourniquet is placed proximal to the fetlock
immediately prior to injection (vein will be maximally distended immediately after the tourniquet is placed). Three sites
of injection are available. One vein runs down the center of the dorsal aspect of the pastern. Another vein runs approximately
2 cm dorsal to the dewclaw, on both the lateral and medial sides of the foot. A 20-gauge needle or butterfly catheter is inserted
into one of these veins and 15 cc to 20 cc of local anesthetic agent is administered. Alternatively, a 20-gauge, 1.5-inch
needle is inserted into the dorsal aspect of the pastern, in the groove between the proximal phalanges, just distal to the
fetlock. Many times a vein is entered in the interdigital space and can be used to inject the anesthetic agent. It is only
necessary to administer an anesthetic into one of these veins to provide anesthesia to the entire area distal to the tourniquet.
The tourniquet can be safely left on for up to an hour to provide hemostasis during surgical procedures.
In feet with severe cellulitis, local intravenous anesthesia can be difficult. In these cases, a four-point nerve block or
a simple ring block will also work. The four-point nerve block anesthetizes the area from the pastern distally. To perform
the procedure, a 20-gauge, 1-inch needle is inserted into the dorsal aspect of the pastern, in the groove between the proximal
phalanges, just distal to the fetlock. Five mls of lidocaine is administered deep, and another 5 mls superficially. This injection
is repeated on the palmar/plantar aspect of the pastern, just distal to the dewclaws. Next, palpate the nerve over the lateral
aspect of the fetlock, approximately 2 cm dorsal and proximal to the dewclaw. Administer 5 mls of lidocaine over the nerve
and repeat on the medial side. The two interdigital injections performed in the four-point block can be used for removal of
an interdigital fibroma.
Most bovine practitioners are familiar with the use of lidocaine and/or carbocaine for caudal epidural anesthesia. But other
pharmacologic agents can be used with this technique. Epidural administration of xylazine (0.05 mg/kg) or xylazine/lidocaine
combination offers similar anesthesia to lidocaine but the duration is longer (~4 hours) and systemic effects (sedation, salivation,
ataxia) can occur. Because of the systemic effects, I do not use xylazine caudal epidurals for obstetric work. However, I
have used it successfully in cattle that chronically strain due to rectal or vaginal prolapse, vaginal irritation, etc. Although
the duration of anesthesia is still relatively short, it's my opinion that the systemic sedation effects are helpful in decreasing
straining. I have not experienced problems with this technique; however, Dr. Lyle George reports three cases of demyelination
following xylazine epidural that caused these animals to be permanently paralyzed. He suggests that combination of lidocaine
or carbocaine caudal epidural with systemic administration of xylazine is as effective as xylazine epidural administration
and has less potential for serious side effects.
Epidural administration of opioids is another option for practitioners. Because they cause analgesia, but do not interfere
with motor function, animals are less likely to become ataxic or recumbent. Also, the duration is longer (~12 hours for morphine).
The disadvantages are that the analgesia is not as potent as lidocaine or carbocaine, and maximum effects of a morphine epidural
may not occur for 2 hours to 3 hours or longer. Caudal epidural administration of morphine might be indicated for relief of
pain in the perineum and to help reduce straining. Lumbosacral epidural administration of morphine may reduce pain during
and after standing surgical procedures and may be used for pain relief in the rear limbs and pelvis. For maximum effects during
surgery, lumbosacral epidural administration of morphine should be administered at least 2 hours to 3 hours prior to surgery,
and routine local anesthetic techniques to anesthetize the flank should still be employed. The dose of morphine for epidural
injection is 0.1 mg/kg diluted in 20 mls of sterile saline.
The combination of morphine and xylazine might be synergistic when administered epidurally.
Morphine (40 mg to 100 mg) can be injected directly into a joint, or used in the regional intravenous technique in the foot.
Morphine used in this manner may not totally eliminate pain, but may reduce the amount of other analgesics needed, such as
non-steroidal anti-inflammatory drugs, or NSAIDs.