/// QUARTERLY BEAT / OCTOBER 2022
QUARTERLY BEAT / OCTOBER 2022 ///
plane of the head. The area desensitized by the block depends on placement of the needle and the volume used. If the local anesthetic is placed outside of the canal, only the ipsilateral skin of the nose and the upper lip are desensitized. If the drug in placed in the canal (by inserting the needle in the canal and/ or by increasing the volume and gentle pressure with the finger on the injection site) some premolar, canine, incisor teeth and associated soft tissues will be desensitized as well. Mental Nerve Block: This block is performed with the animal in lateral recumbency with the side to be blocked facing up. The middle mental foramen can be identified by palpating the root of the second premolar in dogs and the area between the canine and third premolar in cats. A transcutaneous or transmucosal approach can be used. The needle is placed between the finger palpating the foramen and the lateral aspect of the mandible and the local anesthetic is injected. This block only desensitizes the rostral lower lip. If the needle is placed inside the mental canal, the rostral inferior alveolar nerve can be blocked desensitizing also premolar, canine, and incisor teeth. LOCAL BLOCKS FOR THE LIMBS Most blocks can be performed using a nerve locator and/or an ultrasound machine to localize the nerves. Bupivacaine 0.5% or ropivacaine 0.5% are generally used. Doses and volumes may vary depending on the specific nerve and location. Insulated needles are used for nerve stimulation with a nerve locator. Most of these needles can also be seen with an ultrasound; however, if only the ultrasound machine is used to localize the nerve, a spinal needle will be sufficient. Brachial plexus block: This block provides anesthesia to the distal humerus and everything distal to this location. It can be performed with a nerve locator, with an ultrasound or with both techniques. The use of an ultrasound increases the chance of a complete block. When using a nerve stimulator alone, the animals is positioned in lateral recumbency with the affected leg in a non-dependent position. The block is performed by palpating the point of shoulder and the first rib and inserting a long needle parallel to the spinal cord. The index on the non- dominant hand that is palpating the first rib can be used to protect the chest cavity and the needle can be inserted above of the index. Risks include hemorrhage and pneumothorax. When using an ultrasound machine, the animal is placed in dorsal recumbency with the affected leg flexed in neutral position. The linear transducer is positioned in the axillary space and a spinal or insulated needle is inserted in-plane cranio-caudally. The nerve bundle is located cranial to the axillary artery. The total volume of local anesthetic used is approximately 0.3-0.4 ml/kg of 0.5% bupivacaine or ropivacaine.
RUMM block: This block anesthetizes the radial nerve (lateral approach) and the ulnar, musculocutaneous, and median nerves (medial approach). It is indicated for surgical procedures of the thoracic limb distal to the elbow (antebrachium, carpus, and foot). When using a nerve stimulator alone, the needle is inserted in the lateral aspect of the limb between the middle third and the distal third of the line connecting the point of the shoulder and the lateral epicondyle of the humerus. To block the medial nerves (ulnar, musculocutaneous, and median), the needle is inserted in the half-way point of the line connecting the point of the shoulder and the medial epicondyle of the humerus avoiding the biceps brachii muscle. When using the ultrasound, the linear transducer is placed transverse to the longitudinal axis of the humerus (same location described for the nerve locator technique). The needle is inserted in-plane cranio-caudally. The radial nerve is hyperechoic and is located caudal to the humerus between the brachialis and the triceps brachii muscles. To block the medial nerves, the transducer is placed on the medial aspect of the limb at the level of the mid-diaphysis of the humerus. Just caudal to the humerus, the brachial artery can be identified and the brachial vein is located caudal to the artery. The median and ulnar nerves can be found between these two vessels and the musculocutaneous nerve is located cranial to the brachial artery. The volume of local anesthetic used for these blocks is 0.2-0.3 ml/kg of 0.5% bupivacaine or ropivacaine, half for the radial nerve and the other half for the medial nerves. Bier block: This block, also known as intravenous regional anesthesia, is used to anesthetize the thoracic or pelvic limb caudal to the injection site of the local anesthetic. It is paramount to use lidocaine instead of bupivacaine or ropivacaine due to their cardiotoxicity. After prepping the limb, an intravenous catheter is placed proximal to the area of interest and directed distally. An Esmarch bandage is applied starting from the distal portion of the leg until the IV catheter is covered to remove the blood from the limb. A tourniquet is then applied at the proximal end of the bandage to prevent blood from perfusing the distal limb and the bandage is removed. A dose of 6 mg/kg of 2% lidocaine is injected in the IV catheter before the surgical procedure starts. The tourniquet should be removed after 60- 90 minutes from its application to avoid nerve injury. Once the tourniquet is removed, the local anesthesia of the block ends and systemic analgesia should be provided. Sciatic and femoral-saphenous nerve blocks: Both sciatic and femoral-saphenous nerve blocks are required to anesthetize structures distal to the mid femur. When using the nerve locator alone, the patient is positioned in lateral recumbency with the affected leg up. With the non-dominant hand, the operator palpates the greater trochanter of the femur and the ischiatic tuberosity. The insulated needle is inserted halfway between these two points and perpendicular to the skin in the biceps femoris muscle until the contraction/extension of the
WEBINAR HIGHLIGHTS
MICHELE BARLETTA , DVM, MS, PHD, DACVAA University of Georgia, College of Veterinary Medicine, Department of Large Animal Medicine, Athens GA Local Anesthetic Blocks of the Head and Limbs
In this VETgirl anesthesia webinar “Ten Most Popular Local Nerve Blocks in Small Animals,” Michele Barletta, DVM, MS, PhD, DACVAA discusses how to improve your analgesia in your small animal patients with the use of local anesthesia blocks. In these proceedings, he reviews local blocks of the head and limbs. Missed the webinar? Check it out HERE!
margin of the mandible and on its medial side. Avoid the lingual nerve by keeping the needle as close as possible to the mandible. Maxillary nerve block: This block desensitizes the ipsilateral upper lip, skin of the nose, mucosa of soft and hard palate, maxilla including the teeth and associated soft tissues. This block can be performed using 3 approaches: 1. Intraoral: the animal’s mouth is kept open (use mouth gag) and the needle is inserted caudal to the last molar perpendicular to the hard palate. 2. Subzygomatic: the needle is inserted through the skin perpendicular to the median plane of the head. The point of insertion is ventral to the zygomatic arch and between the caudal aspect of the maxilla and the coronoid process of the mandible. 3. Infraorbital: after identification of the infraorbital foramen via palpation (dorsal to the 3rd maxillary premolar, rostroventral to the eye) a thin needle or a catheter is inserted in the infraorbital canal to reach the caudal position and exit the maxillary foramen where the local anesthetic is deposited. There is a higher risk of damaging neurovascular structures in the canal when a needle is use. To avoid nerve damage, use a catheter instead of a needle. Once the catheter is close to the foramen, advance only the catheter in the canal without the stylet. Infraorbital Nerve Block: The identification of the infraorbital canal can be done via palpation (see “Maxillary Nerve Block, infraorbital approach” for location). The needle is inserted through the skin (transcutaneous approach) or the mucosa (transmucosal approach) with the syringe parallel to the median
LOCAL BLOCKS FOR THE HEAD General anesthesia or heavy sedation are required to perform local blocks for dental procedures in small animals. Needle size and volume of the local anesthetic injected vary based on location and size of the animal. Generally, 25- to 30-gauge, 12-25 mm long needles are used. Bupivacaine, ropivacaine or lidocaine are usually selected and volumes injected are between 0.2 and 2.5 ml (total volume per block). Always calculate the maximum dose you can inject and do not exceed that limit. For bupivacaine and ropivacaine stay under 1.5-2 mg/kg in dogs and cats, for lidocaine 6 mg/kg in dogs and 2-3 mg/kg in cats. Once the needle is placed close to the nerve that needs to be desensitized, always aspirate before performing the block to make sure you are not injecting the local anesthetic into a vessel. Inferior alveolar nerve block: This block desensitizes the ipsilateral lower lip, mandibular teeth and associated soft tissues. It can be performed using 2 approaches: 1. Intraoral: the mandibular foramen is palpated just caudal to the last molar while the mouth is kept open. The use of an appropriate mouth gag is recommended to protect the operator’s hand in case the animal is not adequately sedated/anesthetized. The needle is directed ventrocaudally on the medial side of the mandible aiming towards the angle of the mandible. It is important to stay as close as possible to the mandible to avoid blocking the lingual nerve. 2. Extraoral: with the animal in lateral recumbency, the uppermost mandibular foramen is palpated intraorally (use mouth gag). The needle is placed close to the foramen by inserting it through the skin perpendicular to the ventral
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