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An Urban Experience
prior to local anaesthetic injection, should always be performed, as local anaesthetics (with the exception of lidocaine in certain circumstances) should never be given intravascularly. Intravenous administration or overdose
of local anaesthetics can cause cardiotoxic (peripheral vasodilation, hypotension, decreased myocardial contractility and arrythmias) or neurotoxic (sedation, disorientation, ataxia, convulsions) side effects.
Limb blocks
Local blocks are an excellent choice for orthopaedic patients as most aspects of limbs can be desensitized using a number of different regional blocks.
Intra-articular analgesia
This is a simple local anaesthetic block which can be done pre-or post any surgery involving a joint, including arthroscopy. As with all local anaesthetic blocks, it must be done in a strictly aseptic manner to avoid introducing infection into the joint. This technique should be carried out as a ‘one-off’ rather than as a continuous infusion. As with all analgesia, pre-emptive administration is
best, and so ideally the drug should be injected before surgery (often this can be performed once a joint tap has been performed, using the same needle left in place). Alternatively, it can be injected at the end of surgery just before the joint is closed. Bupivacaine is used as the local anaesthetic of choice, but in animals with chronic joint disease morphine can also be added to the local anaesthetic. In such cases of chronic joint in ammation, synovial opioid receptors are upregulated, and morphine should improve the quality and the duration of the analgesia.
Brachial plexus block
Blocking the nerves of the brachial plexus will provide excellent analgesia for procedures below the elbow.
The traditional brachial plexus (axillary) block, injecting approximately 10–15 ml of local anaesthetic (for a 25 kg dog) into the axillary space at the level of the point of the shoulder blocks the lower forelimb, but not the shoulder or the proximal humerus.
1. The patient should be positioned in lateral recumbency with the leg to be blocked placed uppermost, being held in a natural position (perpendicular to the longitudinal axis of the body)
2. The proposed puncture site should be clipped and aseptically prepped
3. lnsert a spinal needle into the axillary region, medial to and at the level of the shoulder joint, directed toward the costochondral junction and parallel to the vertebral column.
4. The needle’s distal end should lie just caudal to the spine of the scapula.
5. As with any local block, aspirate the syringe to avoid intravascular administration, and then inject two-thirds
of the dose. Inject the remaining one-third as you slowly withdraw the needle.
6. Increasing the volume of local anesthetic used by diluting it with sterile saline solution up to 50% can improve the degree of blockade by increasing the volume injected.
Pneumothorax is a potential complication of both of these brachial plexus blocks and aspiration to check for air should be performed before each injection. Bilateral blocks should be avoided due to potential blockade of the phrenic nerve.
Pelvic limb blocks
The sciatic nerve block may be combined with either
a femoral nerve or lumbar plexus block to provide analgesia for pelvic limb surgery. Electro neurolocation is recommended for these techniques to improve accuracy, ensure safety and reduce the dose of local anaesthetic required. It is also unlikely satisfactory local anaesthesia will be gained without electro-neurolocation. The sciatic nerve is blocked at its proximal location caudal to the greater trochanter of the femur. The puncture site is located at the junction of the cranial and middle thirds between a line drawn between the greater trochanter of the femur and the ischial tuberosity. The depth of needle insertion varies depending on the size of patient and may be up to 6cm to 8cm. The femoral nerve is blocked at
its location on the medial aspect of the pelvic limb in the femoral triangle. The femoral artery is palpated within the femoral triangle, held in place with light digital pressure and the femoreal nerve is located and blocked cranial to the artery, usually in a super cial location. An alternative to the femoral nerve block is the lumbar plexus block, which allows for the femoral nerve to be blocked more proximally and avoids the risk of missing the saphenous nerve high within the inguinal region. The saphenous nerve supplies the cutaneous innervation to the sti e and therefore if missed a patient may respond to skin incision. The lumbar plexus block is performed with the patient positioned in lateral recumbency with the side to be blocked uppermost. The dorsal process of L7 is palpated and from this the dorsal process of L5 identi ed. The needle is inserted lateral to L5 (approximately 2cm to 3cm) until the transverse process is contacted. The needle is then walked off bone caudally and a loss
of resistance may be felt as it passes through the intervertebral ligament. Local anaesthetic is then injected after aspiration.

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