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Sciatic and femoral nerve blocks in cats: evaluation of bupivacaine distribution under nuclear magnetic resonance and antinociceptive assessment

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Author(s):
Marina Cayetano Evangelista
Total Authors: 1
Document type: Master's Dissertation
Press: São Paulo.
Institution: Universidade de São Paulo (USP). Faculdade de Medicina Veterinária e Zootecnia (FMVZ/SBD)
Defense date:
Examining board members:
Denise Tabacchi Fantoni; Adilson Hamaji
Advisor: Denise Tabacchi Fantoni
Abstract

Peripheral nerve blocks are practic, effective and widely used for the perioperative pain management, however studies in cats are scarce. The aim of this study was to evaluate the distribution of bupivacaine after sciatic (ScN) and femoral nerve (FN) blocks in cats using magnetic resonance imaging (MRI) and to determine the feasibility, effectiveness and duration of antinociception after ScN and FN blocks using bupivacaine alone, or in combination with either dexmedetomidine or buprenorphine. In the first phase of the study, six adult cats were anesthetized with isoflurane and underwent MRI. Transverse and sagittal plan sequences of pelvic limbs were obtained. The ScN and FN blocks were performed using an electric nerve stimulator-guided technique and bupivacaine 0.5% (0.1 mL/kg per site). The MRI sequences were repeated after each block and the images were analyzed according to the distribution (1; in contact with the nerve or 0; not in contact with the target nerve), bupivacaine location and presence or absence of hematomas and nerve injuries. In the second phase of the study, six adult cats were sedated with dexmedetomidine (25 &micro;g/kg) and received the ScN and FN blocks with 0.1 mL/kg of one of the treatments: saline 0.9% (CONTROL), bupivacaine (0.46%; BUPI), bupivacaine and dexmedetomidine (1 &micro;g/kg; BUPI-DEX) or bupivacaine and buprenorphine (2.5 &micro;g/kg; BUPI-BUPRE). Atipamezole (250 &micro;g/kg) was administered for reversal of sedation. Sedation scores, paw withdrawal thresholds, ability to walk and response to toe pinch were evaluated up to 24 hours after the blocks. According to MRI, five out of six ScN injections had distribution score of 1. Mean ± SD length of the ScN in contact with bupivacaine was 25 ± 11 mm. All FN injections had distribution score of 1. In one injection (FN), bupivacaine was administered distal to the bifurcation between the femoral and saphenous nerve and over the motor branch of FN. Nerve injury or acute hemorrhage were not observed. Nerve stimulator-guided ScN and FN injections produced a reliable bupivacaine spread over the target nerves and the volume was considered sufficient. Individual variability in regards to the injectate location may explain differences in sensory and motor blockade in the clinical setting. All local anesthetic-treated animals had motor function impairment and changes in antinociception. Walking ability was impaired in BUPI from 30 min to 2 hours, in BUPI-DEX between 1 and 2 hours and in BUPI-BUPRE at 2h (p < 0.05). Motor blockade was observed between 1 and 3 hours. Analgesia, determined by paw withdraw threshold, was higher from 1 to 6 hours in BUPI compared to CONTROL (p < 0.05) and reached values greater than 2.4 N from 1 to 4 hours in BUPI-DEX and BUPI-BUPRE and from 1 to 8 hours in BUPI. The chosen doses of buprenorphine and dexmedetomidine as adjuvant drugs did not enhance the magnitude and duration of the ScN and NF blocks in cats (AU)

FAPESP's process: 15/01712-0 - Assessment of bupivacaine alone or in combination with dexmedetomidine or buprenorphine for sciatic and femoral nerve blocks in cats
Grantee:Marina Cayetano Evangelista
Support Opportunities: Scholarships in Brazil - Master