Local Anesthesia in Dogs and Cats



Local Anesthesia in Dogs and Cats




Overview


Local anesthetic techniques can be used in small animals to perform medical and surgical procedures while avoiding the depressant effects of general anesthesia. Local anesthesia is usually administered in combination with sedation or tranquilization to produce a pain-free, cooperative patient. Local analgesic techniques can also be used to produce postoperative analgesia in animals undergoing general anesthesia and surgery. Ultrasound-guided techniques can be used to identify nerves, reduce the total amount of local anesthetic required to produce a nerve block, and improve safety. Commonly used techniques in small animals include infiltration anesthesia, selected nerve blocks, brachial plexus block, intravenous (IV) regional anesthesia, and continuous epidural anesthesia. Epidural opioid, α2-agonist, or ketamine analgesia; intercostal nerve blocks; and intrapleural analgesia can provide longer-lasting postoperative pain relief (up to 12 hours from a single injection).




Regional Anesthesia of the Head




Anesthesia of the upper lip and nose



Area blocked: upper lip and nose, roof of nasal cavity, and related skin ventral to the infraorbital foramen


Nerve blocked: infraorbital


Site: point of emergence of the nerve from the infraorbital canal (Figs. 7-1, A, and 7-2, A)




Needle: 22- to 25-gauge, 2.5- to 5-cm


Anesthetic: Use 1-2 ml of the chosen anesthetic or anesthetic combination. Do not exceed 1.5 mg of lidocaine/kg of body weight with or without 1.5 mg of bupivacaine or ropivacaine/kg


Method: insert the needle either intraorally or extraorally about 1 cm cranial to the bony lip of the infraorbital foramen; advance the needle to the infraorbital foramen, which can be felt between the dorsal border of the zygomatic process and the gingiva of the canine tooth


II Anesthesia of maxilla, upper teeth, nose, and upper lip



Area blocked: maxilla, upper teeth, nose, and upper lip


Nerve blocked: maxillary


Site: perpendicular portion of the palatine bone between the maxillary foramen and foramen rotundum (Figs. 7-1, B, and 7-2, B)


Needle: 22- to 25-gauge, 2.5- to 5-cm


Anesthetic: 1-2 ml of the chosen anesthetic or anesthetic combination. Do not exceed 1.5 mg of lidocaine/kg with or without 1.5 mg of bupivacaine or ropivacaine/kg


Method: insert the needle through the skin at a 90-degree angle, in a medial direction, ventral to the border of the zygomatic process and about 0.5 cm caudal to the lateral canthus of the eye; advance the needle in close proximity to the pterygopalatine fossa; local anesthetic is administered where the maxillary nerve courses perpendicular to the palatine bone between the maxillary foramen and foramen rotundum


III Anesthesia of the eye



Area blocked: eye, orbit, conjunctiva, eyelids, and forehead skin


Nerves blocked: lacrimal, zygomatic, and ophthalmic (i.e., ophthalmic division of the trigeminal nerve)


Site: at the orbital fissure (Figs. 7-1, C, and 7-2, C)


Needle: 22- to 25-gauge, 2.5-cm


Anesthetic: 1-2 ml of the chosen anesthetic or anesthetic combination . Do not exceed 1.5 mg of lidocaine/kg with or without 1.5 mg of bupivacaine or ropivacaine/kg


Method: insert the needle ventral to the border of the zygomatic process at the lateral canthus of the eye; the needle point should be about 0.5 cm cranial to the anterior border of the vertical portion of the ramus of the mandible; advance the needle medial to the ramus of the mandible in a mediodorsal and somewhat caudal direction until it reaches the orbital fissure


IV Anesthesia of the lower lip



Anesthesia of the mandible and lower teeth




Anesthesia of the Foot





Brachial Plexus Block




Area blocked: distal foot, up to the elbow region


II Nerves blocked: radial, median, ulnar, musculocutaneous, and axillary nerves


III Site: medial to the shoulder joint (Fig. 7-4)



IV Needle: 20- to 22-gauge, 7.5-cm (3.7-cm in cats); a spinal needle or catheter stylet works well


Anesthetic: 5- 10 ml of the chosen anesthetic or anesthetic combination. Do not exceed 1.5 mg of lidocaine/kg with or without 1.5 mg of bupivacaine or ropivacaine/kg


VI Method:



Insert the needle medial to the shoulder joint toward the costochondral junction and parallel to the vertebral column


Inject the anesthetic slowly as the needle is withdrawn; anesthesia can be obtained within 20 minutes and for up to 2 hours (total recovery requires about 6 hours)


Alternatively, use the same needle placement technique but use a nerve locator and insulated needle



Advantages



Disadvantages



Complications




Ultrasound Guided Rear Limb Block (sciatic and femoral nerve blocks)




Area blocked: The femoral nerve innervates the cranial muscles of the thigh. All remaining muscles of the limb are innervated by the sciatic nerve.


II Site: The femoral nerve is imaged at the medial aspect of the thigh. The sciatic nerve is imaged just distal and caudal to the greater trochanter.


III Needle: 22-gauge, 2.5 to 3.7 cm


IV Anesthetic: 2-4 mL (total) of the chosen anesthetic or anesthetic combination. Do not exceed 1.5 mg of lidocaine/kg with or without 1.5 mg of bupivacaine or ropivacaine/kg


Method:



Clip the hair from the sacroiliac region just below the stifle on the dorsal, lateral, and medial aspects of the limb


Clean the skin and apply coupling gel


For the sciatic nerve block, place the dog in lateral recumbency



1. Place the ultrasonic transducer on the transverse plane just distal and caudal to the greater trochanter and then direct it towards the distal aspect of the thigh (Figs. 7-5 and 7-6)




2. The sciatic nerve is imaged from the dorsal aspect. Transverse images can also be obtained by positioning the transducer parallel to the dorsal anatomical plane caudal to the greater trochanter and cranial to the ischiatic tuberosity. Longitudinal images of the sciatic nerve can be obtained by rotating the transducer 90 degrees from the position used to obtain the transverse images. Several acoustic windows are available to approach this nerve along the lateral surface of the thigh.


Approach of the femoral nerve. This description uses a mid-femur approach. The femoral nerve is imaged at the medial aspect of the thigh. Position the dog in lateral recumbency.



Both the sciatic and femoral nerves are approached using the acoustic windows described earlier. The accuracy of the nerve location is confirmed by use of a peripheral nerve stimulator.


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Sep 6, 2016 | Posted by in SUGERY, ORTHOPEDICS & ANESTHESIA | Comments Off on Local Anesthesia in Dogs and Cats

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