Desenvolvimento de técnica para bloqueio dos nervos medianoulnar e radial em patos (Cairina moschata)

Abstract

The success of peripheral nerve blocking techniques requires precise knowledge of the anatomical area to be blocked, thus yielding accurate local anesthetic administration and a reduction on the anesthetic dosage. The aim of this study was to develop a regional anesthesia method for locomotor appendage. We performed anesthetic block of median ulnar and radial nerves in muscovy duck (Cairina moschata) with 2% lidocaine guided by peripheral nerve stimulator, followed by evaluation of effectiveness in ex vivo and in vivo studies. For anatomical study we used six cadaver ducks and in two of these was also performed the radiographic examination of the spine. Based on the anatomical study we defined and described two access points to block the forelimb. In a muscovy duck body methylene blue was injected with subsequent dissection and observation of the nerve and the surrounding regions’ colors. In vivo studies were performed in domestic duck specimens, consisting of an initial pilot study with two animals to determine the electric system for neurolocalization and later evaluation of the motor and nociceptive response to blockage of medianoulnar and radial nerve in six duck specimens, female, adult, middle weight 1,42kg. After induction with isoflurane, animals underwent neurolocalization technique by starting the nerve stimulation with a current of 0.7 mA, frequency of 2 Hz and pulse duration of 300 Seg. We gradually decreased the current to 0.2 mA to induce a motor response, and 0.18 mA to induce no response. Each animal had one wing injected with lidocaine 2% (6 mg/kg), being the Treated Group, and a wing injected with the same volume of saline 0.9%, being the Control Group, in blind technique. Isoflurane was then interrupted. The evaluation of sensory and motor response was expressed as scores and started 3 minutes after extubation, followed by observation at 5, 10, 15 and 20 minutes, and then every 10 minutes untill the end of the block. Radiographic examination of the spine and the anatomical study revealed that the duck has four roots that unite into a single trunk and then originate the major nerves: axillary, radial, medianoulnar and breastplate. During the methylene blue dispersion study, nerves were presented pigmented to a large extent, demonstrating that the application points and the volume of anesthetic applied were satisfactory. The in vivo study showed a statistically significant difference in scores of muscle relaxation between the treated and control groups in times 5-40 minutes and sensory block in times 3-50 minutes. The duration of sensory block ranged between 37-77 minutes (mean 51.67 + 17.28 minutes). We concluded that the medianoulnar and radial nerve block technique guided by peripheral nerve stimulator was effective when using 6 mg/kg of lidocaine, with successful blockade distal to the humerus-radio-ulnar joint.