Management of Urethral Obstruction in a Cat with Epidural Sacrococcygeal Anesthesia Guided by Electrical Neurostimulation
Background: The treatment for urethral obstruction in cats consists of catheterization, and for this, the cat must be sedated or anesthetized. Sacococcygeal epidural block has the advantage of being close to receptors related to nociception located in the spinal cord and it is safer because it represents lower risk of spinal cord injury or inadvertent application in the subarachnoid space, when compared to the lumbosacral epidural. Nerve stimulation through the neurolocator to identify the epidural space increases the accuracy of this technique. Thus, the objective is to report a case of epidural anesthesia with a sacrococcygeal approach guided by neurostimulation in a cat with urethral obstruction.
Case: A 4-year-old male Siamese cat, weighing 4 kg, was referred to the veterinary care with a history of apathy and anorexia for 2 days. From the physical exam, the clinical diagnosis of urethral obstruction was made, and to desobstruction, we chose to perform sacrococcygeal epidural block. Initially, the patient was anesthetized with propofol (4 mg/kg) and midazolam (0.3 mg/kg). To perform the anesthetic block, the cat was placed in sternal decubitus with the hind limbs extended cranially to perform sacrococcygeal epidural block. The positive pole (cathode) was connected to the skin of the right inguinal region at the caudal aspect of the thigh and the neurostimulator was turned on and adjusted to 0.7 mA of stimulating current intensity, 0.1 ms duration and 1 Hz frequency. The needle for electrical neurolocation was introduced in the dorsal midline, perpendicular to the skin surface, between the spinous processes of S3-Cd1 in the skin. The exact injection point was obtained observed by the muscular response of the middle and distal third of the animal’s tail with the neurostimulator adjusted to 0.3 mA of intensity, in the same duration and frequency as before. The total volume of 0.9 mL (0.22 mL/kg) of solution containing the combination of 0.6 mL of 0.75% levobupivacaine and 0.3 mL of 2% lidocaine was injected. The success of the block was confirmed by the loss of reflexes of the pelvic limbs and anal sphincter 10 min after the administration of the anesthetic solution.
Discussion: In this case, the use of the neurolocator helped to perform an effective sacrococcygeal block, allowing urethral catheterization without the addition of other analgesic agents. This technique desensitizes and relaxes muscles in the regions of the perineum, anus, distal colon and penis, being useful for performing urethral catheterization. The use of smaller anaesthetic volumes to perform sacrococcygeal block makes it possible to achieve a more localized anesthesia, without affecting the motor function of the pelvic limbs. However, in our report, using a combination of levobupivacaine and lidocaine, the pelvic limb block was also verified despite the low volume applied. A hypothesis that could justify the different responses in relation to the pelvic limb block compared to other studies would be due to the different physicalchemical properties of the drugs used. Lidocaine is known to be less fat-soluble than bupivacaine, so it tends to spread more through the epidural space, in order to result in more extensive blocks. The use of a neurostimulator using a fixed electric current of 0.7 mA, pulse 0.1 ms and a frequency of 1 Hz allowed the correct identification of the needle position for the application of the anesthetic.
Keywords: local block, nerve stimulation, levobupivacaine, lidocaine.
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