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Palpation- and ultrasound-guided brachial plexus blockade in Hispaniolan Amazon parrots (Amazona ventralis)
Veterinary Anaesthesia and Analgesia, 2013, 40, 96–102
doi:10.1111/j.1467-2995.2012.00783.x
RESEARCH PAPER
Palpation- and ultrasound-guided brachial plexus blockade in Hispaniolan Amazon parrots (Amazona ventralis) Anderson F da Cunha*, George M Strain , Nathalie Rademacher*, Rodney Schnellbacherà & Thomas N Tully* *Department of Veterinary Clinical Sciences, Louisiana State University, School of Veterinary Medicine, Baton Rouge, LA, USA Department of Comparative Biomedical Sciences, Louisiana State University, School of Veterinary Medicine, Baton Rouge, LA, USA àDepartment of Small Animal Medicine and Surgery, University of Georgia, College of Veterinary Medicine, Athens, GA, USA
Correspondence: Anderson da Cunha, Department of Veterinary Clinical Sciences, Louisiana State University, School of Veterinary Medicine, Baton Rouge, LA, USA 70803. E-mail: [email protected]
Abstract Objective To compare palpation-guided with ultrasound-guided brachial plexus blockade in Hispaniolan Amazon parrots. Study design Prospective randomized experimental trial. Animals Eighteen adult Hispaniolan Amazon parrots (Amazona ventralis) weighing 252–295 g. Methods After induction of anesthesia with isoflurane, parrots received an injection of lidocaine (2 mg kg)1) in a total volume of 0.3 mL at the axillary region. The birds were randomly assigned to equal groups using either palpation or ultrasound as a guide for the brachial plexus block. Nerve evoked muscle potentials (NEMP) were used to monitor effectiveness of brachial plexus block. The palpation-guided group received the local anesthetic at the space between the pectoral muscle, triceps, and supracoracoideus aticimus muscle, at the insertion of the tendons of the caudal coracobrachial muscle, and the caudal scapulohumeral muscle. For the ultrasound-guided group, the brachial plexus and the adjacent vessels were located with B-mode ultrasonography using a 7–15 MHz linear probe. After location, an 8-5 MHz 96
convex transducer was used to guide injections. General anesthesia was discontinued 20 minutes after lidocaine injection and the birds recovered in a padded cage. Results Both techniques decreased the amplitude of NEMP. Statistically significant differences in NEMP amplitudes, were observed within the ultrasoundguided group at 5, 10, 15, and 20 minutes after injection and within the palpation-guided group at 10, 15, and 20 minutes after injection. There was no statistically significant difference between the two groups. No effect on motor function, muscle relaxation or wing droop was observed after brachial plexus block. Conclusions and clinical relevance The onset of the brachial plexus block tended to be faster when ultrasonography was used. Brachial plexus injection can be performed in Hispaniolan Amazon parrots and nerve evoked muscle potentials were useful to monitor the effects on nerve conduction in this avian species. Neither technique produced an effective block at the doses of lidocaine used and further study is necessary to develop a useful block for surgical analgesia. Keywords analgesia, avian, birds, local anesthesia, nerve evoked muscle potentials, pain.
Brachial plexus blockade in Hispaniolan Amazon parrots AF da Cunha et al.
Introduction The blockade of sensory neurons of the brachial plexus has been investigated as a viable technique for providing analgesia for painful lesions of the wing in avian species (Figueiredo et al. 2008; Cardozo et al. 2009; Brenner et al. 2010), prevent pain during surgical treatments (Futema et al. 2002), and an adequate way to avoid central pain sensitization (Tryba 1998) and treat chronic pain (Mukherji et al. 2000). Furthermore, regional anesthesia can be used as a sole technique for anesthesia and analgesia in surgical procedures performed under sedation or light anesthesia and as a postoperative analgesic technique following invasive surgeries (Machin 2005). In avian medicine, brachial plexus blockade has been described in the chicken (Gallus gallus domesticus) (Figueiredo et al. 2008; Cardozo et al. 2009), mallard duck (Brenner et al. 2010) and, in a clinical case presentation, in the cockatiel (Nymphicus hollandicus), a free-ranging striped owl (Asio clamator) and in roadside hawks (Rupornis manirostris) (Vilani et al. 2006). Even though some anatomical and physiological differences are observed between avian and mammalian species, the basic pathophysiology of pain is comparable (Machin 2005). Taking these similarities into consideration, it is appropriate to suggest that brachial plexus blockade is a valuable technique for analgesia of the wings of avian species. An effective brachial plexus nerve block is achieved by injecting a local anesthetic close to the brachial plexus and subsequent diffusion of the drug into the perineural space (Neal et al. 2002; Campoy et al. 2010). However, the anatomic location of the brachial plexus varies greatly among avian species. In this sense a technique described for one species does not necessarily apply to other species. Several techniques have been described to ensure accurate needle placement during the nerve block in different species. Modern tools like ultrasonography have transformed the art of regional anesthesia into a science (Borgeat 2006). The advantages of using ultrasound to guide local anesthetic deposition include: 1) being able to see the needle tip relative to the nerve, artery and vein; 2) visually confirming injection of local anesthetic close to the nerve; and 3) preventing complications such as intra-fascial and intravascular injection of local anesthetic (Marhofer et al. 2005). As a result, ultrasound significantly enhances the effectiveness
of the brachial plexus block technique (Denny & Harrop-Griffiths 2005) and decreases adverse effects (Marhofer et al. 2005). To the authors’ knowledge, ultrasonography has not been described in avian species as a tool to guide brachial plexus blockade. The nerve evoked muscle potential (NEMP) is an electrophysiological technique for monitoring nerve function that makes it possible to assess and quantify the effectiveness of neural blockade by a local anesthetic (Pandin et al. 2006). Brachial plexus sensory nerve conduction velocity and somatosensory evoked potentials have been evaluated in Mallard ducks (Anas platyrhynchos) (Brenner et al. 2008, 2010), but the techniques are technically more challenging to perform, making them less useful clinically. NEMPs are a more useful method of assessing brachial plexus function and have not been previously used to evaluate local anesthesia in psittacine birds. The intent of this study was to compare palpation-guided and ultrasound-guided brachial plexus blockade with lidocaine in Hispaniolan Amazon parrots, examining the time-course of onset of local anesthesia, degree of the muscle relaxation, degree of nociception, and duration of muscle relaxation after brachial plexus blockade. It was hypothesized that the use of ultrasound-guided local anesthesia would improve the accuracy, decrease onset and increase the efficacy of the brachial plexus block. Materials and methods The study was approved by the Institutional Animal Care and Use Committee (IACUC) (Protocol No. 07061). Eighteen adult Hispaniolan Amazon parrots (Amazona ventralis) (mean weight 267 g; range 252–295 g) were obtained from a locally maintained colony. Tap water and food (Kaytee Exact Rainbow Pellets; Kaytee Inc, WI) were available ad libitum. Birds were considered to be healthy on the basis of a general physical examination. In all birds, anesthesia was induced with isoflurane (Isoflo; Abbott Laboratories, IL) in oxygen delivered by face mask. Each bird was intubated with an uncuffed endotracheal tube and connected to a Bain circuit with a flow rate of 200 mL kg)1 minute)1. All birds were positioned in dorsal recumbency on a circulating hot-water blanket (T/Pump; Gaymar industries Inc, NY) and a forced warm air electric cover blanket (Bair Hugger; Arizant Inc, MN), used to provide supplemental heat for the duration of the anesthetic period. Body
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temperature was maintained between 39 and 40 C [the reference interval for body temperature for birds is 39–43 C (West et al. 2007)]. Partial pressure of carbon dioxide in the expired end-tidal gas (PE¢CO2), arterial hemoglobin saturation with oxygen (pulse oximetry, SpO2), heart rate, esophageal temperature, respiratory rate, lead II electrocardiogram (ECG), partial pressure of isoflurane in the expired end-tidal gas (E¢Iso) and inspiratory fraction of oxygen (FiO2) were monitored with the use of a multi-function monitor (Datascope Passport 2; MAQUET, NJ). Once E¢Iso was stable at 1.5% for a minimum of 15 minutes, temperature was between 39 and 40 C and PE¢CO2, ECG, and SpO2 were considered normal, electromyography (EMG) and nerve stimulation electrodes were positioned (Sierra Wave electrodiagnostic system; Cadwell Laboratories, WA). A cathodal stimulating electrode, an insulated 26-gauge needle with insulation stripped from the tip (Uniplex UP, Pajunk Medical Technology, Germany), was inserted between the spinal cord and the brachial plexus near the cervical nerve root outlets, and the anodal electrode was placed subcutaneously within 1 cm of the cathodal electrode. The ground electrode was placed subcutaneously between the stimulating and recording electrodes to minimize stimulus artifact in the EMG recordings. The minimum threshold stimulus current sufficient to elicit a contraction in the distal muscle was recorded as a baseline. Subsequently, stimuli were applied at 1.5· the threshold current. EMGs were recorded between an insulated EMG electrode placed in the belly of a distal limb flexor muscle and a subcutaneous needle reference electrode located over the muscle belly (Fig. 1). Reduction of the muscle evoked potential amplitude following anesthetic injection was used to determine success or failure of the brachial plexus blockade. After instrumentation, baseline measurements were recorded. The birds were randomly assigned to two equal groups (nine birds per group) and received a single injection of 2 mg kg)1 of lidocaine (Xylocaine, AstraZeneca LP, DE) in a total volume of 0.3 mL in the brachial plexus area by either palpation or with the aid of ultrasonography. The injections were done aseptically using a 22-gauge, 3.8 cm insulated needle. In order to be consistent, a total volume of 0.3 mL was achieved by diluting 2 mg kg)1 of 2% lidocaine with 0.9%NaCl. For the palpation-guided group, the injection site was located by palpating the space between the pectoral muscle, 98
triceps and supracoracoideus aticimus muscle, the insertion of the tendons of the caudal coracobrachial muscle, and the caudal scapulohumeral muscle; the needle was inserted at the angle created by these muscles (Fig. 2). Prior to injection, the needle was aspirated in order to confirm that neither an air sac nor blood vessel had been perforated. For the ultrasound-guided group, birds were placed in dorsal recumbency, feathers were plucked in the brachial area caudal to the humerus, and the wing was extended. The brachial plexus and the adjacent vessels were located with B-mode ultrasonography using a 7–15 MHz linear probe or 8-5 MHz
Figure 1 Hispaniolan Amazon parrot with the right wing extended. The arrow represents the site of injection. Letters represent the positioning of the EMG electrodes where A is the recording electrode, B is the ground electrode and C is the anodal electrode. The copper alligator clip on the extended wing is an ECG lead.
Triceps m.
Caudal scapulohumeral m. Site of injection
Pectoral m.
Supracoracoideus aticimus m.
Caudal coracobrachial m.
Figure 2 Diagram of a Hispaniolan Amazon parrot with the right wing extended. The site of injection is the angle created by the pectoral, triceps and supracoracoideus aticimus muscles and the insertion of the tendons of the caudal coracobrachial and the caudal scapulohumeral muscles.
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Brachial plexus blockade in Hispaniolan Amazon parrots AF da Cunha et al.
convex transducer (iU22; Philips, WA). The linear high frequency transducer (7–15 MHz) was used to locate the brachial plexus and a second transducer, a lower frequency (8-5 MHz), lower resolution convex transducer, was used to visualize the injections. The transducer was placed caudally in the brachial area with the transducer head pointed to the contralateral shoulder (Fig. 3). After ultrasonographic identification of the neurovascular bundle (Fig. 4A), a 22-gauge, 3.8 cm insulated needle was inserted and advanced along the longitudinal axis of the ultrasound transducer with the entire shaft of the needle in the path of the beam (Fig. 4B). Lidocaine at a dose of 2 mg kg)1 was then injected into the space. All palpation-guided injections were performed by one investigator (AC), while the ultrasound-guided injections were performed by a second investigator (NR). The amplitudes of the NEMP were recorded prior to the brachial plexus injection at time zero, and at 5, 10, 15, and 20 minutes after injection. After time 20, anesthesia was discontinued and parrots were placed in padded cages for recovery. During recovery the wing position was observed and pinprick of the distal wing was attempted 20 minutes after full recovery. Degree of relaxation of both wings and response to pinprick was recorded. Full recovery was defined as the time at which the parrot was able to perch without imbalance. All EMG amplitudes for each subject were expressed as a percentage of the time 0, to permit comparison. Amplitudes were defined as the difference between onset (O) and peak of response (P) as observed at Figure 5. The NEMP results were analyzed statistically by a one way analysis of variance followed by the Holm-Sidak pairwise
Figure 3 Photograph of a Hispaniolan Amazon parrot in dorsal recumbency, showing the positioning of the ultrasound transducer caudal to the extended wing.
comparison procedure when p £ 0.05 using Sigma Plot 11. (SigmaPlot 11; Systat Software Inc, CA). Results A statistically significant difference in NEMP amplitudes was observed within the palpation-guided group when comparing time 0 to the times of 10, 15, and 20 minutes (Fig. 6). Times 5, 10, 15, and 20 differed significantly from time 0 for the ultrasoundguided group. No statistically significant difference in amplitudes was detected between the two groups at any time (Fig. 6), although amplitudes in the ultrasound-guided group were lower than palpation-guided group at all times after injection. No difference in motor function, muscle relaxation or wing droop was observed between blocked and non-blocked wings. Both techniques produced a dramatic decrease in the amplitude of nerve evoked
(a)
(b)
Figure 4 Gray-scale image of the brachial plexus area with the nerve bundle seen as a hypoechoic area and marked with an asterisk. (a) shows the air sac and is identified as a hyperechoic area with dirty shadowing (arrows). (b) shows the needle in place from caudal area (arrows).
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Neither self-injuries, nor intravenous or air sac injections were observed. The recoveries were unremarkable. Discussion
Figure 5 Example recordings of nerve evoked muscle potentials from an isoflurane anesthetized Hispaniolan Amazon parrot before and at 0, 5 10, 15, and 20 minutes after injection. Each tracing is a single wing muscle evoked potential by stimulation between the spinal cord and the brachial plexus.
Figure 6 Changes in mean ± SD % of nerve evoked muscle potential response amplitude in percentage, compared to time 0 for each bird. Data analyzed statistically by a one way analysis of variance followed by the Holm-Sidak pairwise comparison procedure (*p £ 0.05). The palpationguided group is represented by the line with filled circles and the ultrasound-guided block is represented by the line with open circles. Time 0 represents base line before local anesthesia injection and times 5, 10, 15, and 20 represent time in minutes after injection.
muscle potentials beginning 5 minutes after lidocaine injection (Fig. 6). Nociceptive assessment by pinprick in the distal wing of these parrots was unsuccessful, as the subjects resisted any human interaction preventing us from touching them. 100
In this study, nerve evoked muscle potentials were used as a nerve conduction monitoring tool to evaluate and compare the effectiveness of palpationguided or ultrasound-guided injection of local anesthetic for brachial plexus block in Hispaniolan Amazon parrots. Brachial plexus blockade has the potential to be useful as a regional anesthesia technique, allowing surgical procedures to be performed in the distal extremity of the wing if a reliable and easy to use technique can be developed. The results of the present study indicate a statistically significant decrease in NEMP amplitudes beginning 5 minutes after injection in the ultrasound-guided group and 10 minutes after the injection in the palpation-guided group with no differences among groups at any time point. Based on reduction of the nerve evoked muscle potential, a decrease in motor nerve conduction was observed and, although not measured, a decrease in sensory nerve conduction was assumed. After recovering from general anesthesia the expected muscle relaxation (wing droop) was not observed in any bird. The lack of wing droop in any of the birds of our study may have been due to using an inadequate dose of lidocaine. The effectiveness of a local anesthetic to produce neural blockade is proportional to the concentration and volume of local anesthetic used (Goodman et al. 2006; Stoelting & Hillier 2006). Higher doses of lidocaine have been reported for the brachial plexus block in birds. Brenner et al. (2010) observed inconsistent wing droop using 15 mg kg)1 of lidocaine with epinephrine in Mallard Ducks. Figueiredo et al. (2008) administered 20 mg kg)1 of lidocaine with epinephrine to chickens and observed wing droop in 12 out of 18 subjects (67% success rate). The safety of local anesthetics in birds is controversial because there are no published reports of their effects, especially cardiovascular effects, in any avian species. It is believed that birds are more sensitive than mammals to the cardiovascular effects of local anesthetics, especially small birds (Tranquilli et al. 2007; West et al. 2007), but this perception is based on a report in which budgerigars died after injection with lidocaine at a dose of 67 mg kg)1 (Grono 1961), a dose that would be toxic to any animal. In our
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Brachial plexus blockade in Hispaniolan Amazon parrots AF da Cunha et al.
study, the small body weight of the birds was considered a limiting factor, so for safety we chose a low dose of lidocaine. For consistency all injections were 0.3 mL per bird, and the lidocaine (2%) was diluted with saline; the final concentration of the injections ranged between 1.71 and 1.96 mg mL)1, depending on each bird’s body weight. However, the low concentration of the lidocaine may have been the cause of the lack of muscle relaxation and wing droop observed on recovery. Two possibilities might explain the lack of wing droop in our birds: (1) the low lidocaine concentration and volume may have incompletely blocked the A-beta nerve fibers, or (2) the block may have worn off very quickly. We suggest that the lack of muscle relaxation after the regional block may have some positive benefits as it could decrease the incidence of incoordination and self-injury in birds during recovery. In those studies describing brachial plexus block in birds, wing relaxation was used as an indicator of blockade success (Vilani et al. 2006; Cardozo et al. 2009). In our study, we did not observe wing relaxation following brachial plexus blockade, a finding that accords with the findings of Brenner et al. (2010) who also did not observe wing droop in all of the birds in that study. We believe that the decrease in NEMP after brachial plexus block observed in our study proves that lidocaine had an effect. One limitation of this study is related to the inability to test the sensory components of the block. Thus the results do not prove the full achievement of local anesthesia, and therefore the authors cannot recommend this technique for surgery. Several factors, such as body temperature, general anesthesia, intensity of the electrical stimulus, could add variability to the NEMP results (King & Rampil 1994). We undertook precautions to reduce their influence on the recordings: each bird’s temperature was monitored and maintained within the normal range (39–40 C); the intensity of the electrical stimulus was consistent from parrot to parrot; and isoflurane, the anesthetic of choice for NEMP studies because of its reportedly minimal effect on nerve conduction velocity (King & Rampil 1994; Oh et al. 2010) was used for general anesthesia. The use of ultrasonography to facilitate brachial plexus blocks with local anesthetic has been described previously in other species (Guntz et al. 2009; Campoy et al. 2010), and has been shown to improve the efficacy of the block because the operator can visualize the location of the needle relative to the nerves and the spread of local anesthetic around the
nerves; this reduces complications such as intravascular and intrathoracic injections of local anesthetic (Pandin et al. 2006). The goal of this project was to deposit the lidocaine as close as possible to the brachial plexus, without causing nerve damage, and anesthetize the wing. There was a statistically significant decrease in conduction amplitude between time zero and 5 minutes after injection in the ultrasound-guided group and between time zero and 10 minutes in the palpation-guided group. This difference might suggest a higher accuracy of placement of the drug near the brachial plexus when ultrasound was used, but the lack of statistical difference between groups suggest that similar efficacy between techniques was obtained. Our results agree with Marhofer et al. (2005) who suggested that ultrasonography is a useful tool, with potential to improve the positive outcome of local anesthesia. We add to their conclusions that ultrasonography should be used for loco-regional anesthesia to improve the accuracy of the block in species where the anatomy of the brachial plexus is not well defined in the literature. Furthermore, the amount of local anesthetics could be reduced without changing effectiveness of the sensory block by the aid of the ultrasonography (Marhofer et al. 1998), which is an important factor for small patients where small volumes of local anesthetics have to be used but we were unable to support this assertion with the current study. In this study two ultrasound transducers were used because it was difficult to inject the lidocaine using the linear transducer due to anatomic limitations of the region in these small birds. Linear transducers have better near field resolution, but because of the shape of the thorax and axilla the convex transducer was more appropriate for the injections. No complications such as intravenous injection, thoracic puncture or self-injury during recovery were observed during this study but should always be a concern. The prevention of these common complications was done by aspiration prior to injection to confirm that the needle was not introduced into the vasculature or into the clavicular air sacs, and by allowing recovery from anesthesia in padded cages. Conclusions This study has shown that injection of a dilute lidocaine solution in the region of the brachial plexus in Hispaniolan Amazon parrots has an effect
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on nerve conduction. The onset tended to be faster when using an ultrasound-guided technique but this was not statistically different from the palpation-guided technique. Neither technique, as described in this paper, achieved a complete block and further work needs to be carried out to develop a method that provides surgical analgesia.
References Borgeat A (2006) All roads do not lead to Rome. Anesthesiology 105, 1–2. Brenner DJ, Larsen RS, Pascoe PJ et al. (2008) Somatosensory evoked potentials and sensory nerve conduction velocities in the thoracic limb of mallard ducks (Anas platyrhynchos). Am J Vet Res 69, 1476– 1480. Brenner DJ, Larsen RS, Dickinson PJ et al. (2010) Development of an avian brachial plexus nerve block technique for perioperative analgesia in mallard ducks (Anas platyrhynchos). J Avian Med Surg 24, 24–34. Campoy L, Bezuidenhout AJ, Gleed RD et al. (2010) Ultrasound-guided approach for axillary brachial plexus, femoral nerve, and sciatic nerve blocks in dogs. Vet Anaesth Analg 37, 144–153. Cardozo LB, Almeida RM, Fiuza LC et al. (2009) Brachial plexus blockade in chickens with 0.75% ropivacaine. Vet Anaesth Analg 36, 396–400. Denny NM, Harrop-Griffiths W (2005) Location, location, location! Ultrasound imaging in regional anaesthesia. Br J Anaesth 94, 1–3. Figueiredo JP, Cruz ML, Mendes GM et al. (2008) Assessment of brachial plexus blockade in chickens by an axillary approach. Vet Anaesth Analg 35, 511– 518. Futema F, Fantoni DT, Auler JOC et al. (2002) A new brachial plexus block technique in dogs. Vet Anaesth Analg 29, 133–139. Goodman LS, Gilman A, Brunton LL et al. (2006) Goodman & Gilman’s the pharmacological basis of therapeutics. McGraw-Hill, NY, USA. Grono LR (1961) Anaesthesia of budgerigars. Aust Vet J 37, 463–464.
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Guntz E, Van den Broeck V, Dereeper E et al. (2009) Ultrasound-guided block of the brachial plexus at the humeral canal. Can J Anaesth 56, 109–114. King BS, Rampil IJ (1994) Anesthetic depression of spinal motor neurons may contribute to lack of movement in response to noxious stimuli. Anesthesiology 81, 1484– 1492. Machin KL (2005) Avian analgesia. Semin Avian Exot Pet 14, 236–242. Marhofer P, Schrogendorfer K, Wallner T et al. (1998) Ultrasonographic guidance reduces the amount of local anesthetic for 3-in-1 blocks. Reg Anesth Pain Med 23, 584–588. Marhofer P, Greher M, Kapral S (2005) Ultrasound guidance in regional anaesthesia. Br J Anaesth 94, 7–17. Mukherji SK, Wagle A, Armao DM et al. (2000) Brachial plexus nerve block with CT guidance for regional pain management: initial results. Radiology 216, 886–890. Neal JM, Hebl JR, Gerancher JC et al. (2002) Brachial plexus anesthesia: essentials of our current understanding. Reg Anesth Pain Med 27, 402–428. Oh SS, Hayes JM, Sims-Robinson C et al. (2010) The effects of anesthesia on measures of nerve conduction velocity in male C57Bl6/J mice. Neurosci Lett 483, 127–131. Pandin P, Salengros JC, d’Hollander A et al. (2006) Somatosensory evoked potentials as an objective assessment of the sensory median nerve blockade after infraclavicular block. Can J Anaesth 53, 67–72. Stoelting RK (2006) Pharmacology and physiology in anesthetic practice. Lippincott-Raven, Philadelphia, PA, USA. Tranquilli WJ, Thurmon JC, Grimm KA et al. (2007) Lumb & Jones’ Veterinary Anesthesia and Analgesia. Blackwell Pub., Ames, Iowa. Tryba M (1998) 6 Prevention of chronic pain syndromes by anaesthetic measures: fact or fiction? Baillie`re’s Clin Anaesthesiol 12, 133–145. Vilani RGDG, Montiani-Ferreira F, Lange RR (2006) Brachial plexus blocks in birds. Exotic DVM 8, 86–91. West G, Heard DJ, Caulkett N (2007) Zoo Animal and Wildlife Immobilization and Anesthesia. Blackwell Pub., Ames, IA, USA. pp. 272. Received 27 May 2011; Accepted 23 September 2011
Published 2012. This article is a U.S. Government work and is in the public domain in the USA, 40, 96–102
doi:10.1111/j.1467-2995.2012.00783.x
RESEARCH PAPER
Palpation- and ultrasound-guided brachial plexus blockade in Hispaniolan Amazon parrots (Amazona ventralis) Anderson F da Cunha*, George M Strain , Nathalie Rademacher*, Rodney Schnellbacherà & Thomas N Tully* *Department of Veterinary Clinical Sciences, Louisiana State University, School of Veterinary Medicine, Baton Rouge, LA, USA Department of Comparative Biomedical Sciences, Louisiana State University, School of Veterinary Medicine, Baton Rouge, LA, USA àDepartment of Small Animal Medicine and Surgery, University of Georgia, College of Veterinary Medicine, Athens, GA, USA
Correspondence: Anderson da Cunha, Department of Veterinary Clinical Sciences, Louisiana State University, School of Veterinary Medicine, Baton Rouge, LA, USA 70803. E-mail: [email protected]
Abstract Objective To compare palpation-guided with ultrasound-guided brachial plexus blockade in Hispaniolan Amazon parrots. Study design Prospective randomized experimental trial. Animals Eighteen adult Hispaniolan Amazon parrots (Amazona ventralis) weighing 252–295 g. Methods After induction of anesthesia with isoflurane, parrots received an injection of lidocaine (2 mg kg)1) in a total volume of 0.3 mL at the axillary region. The birds were randomly assigned to equal groups using either palpation or ultrasound as a guide for the brachial plexus block. Nerve evoked muscle potentials (NEMP) were used to monitor effectiveness of brachial plexus block. The palpation-guided group received the local anesthetic at the space between the pectoral muscle, triceps, and supracoracoideus aticimus muscle, at the insertion of the tendons of the caudal coracobrachial muscle, and the caudal scapulohumeral muscle. For the ultrasound-guided group, the brachial plexus and the adjacent vessels were located with B-mode ultrasonography using a 7–15 MHz linear probe. After location, an 8-5 MHz 96
convex transducer was used to guide injections. General anesthesia was discontinued 20 minutes after lidocaine injection and the birds recovered in a padded cage. Results Both techniques decreased the amplitude of NEMP. Statistically significant differences in NEMP amplitudes, were observed within the ultrasoundguided group at 5, 10, 15, and 20 minutes after injection and within the palpation-guided group at 10, 15, and 20 minutes after injection. There was no statistically significant difference between the two groups. No effect on motor function, muscle relaxation or wing droop was observed after brachial plexus block. Conclusions and clinical relevance The onset of the brachial plexus block tended to be faster when ultrasonography was used. Brachial plexus injection can be performed in Hispaniolan Amazon parrots and nerve evoked muscle potentials were useful to monitor the effects on nerve conduction in this avian species. Neither technique produced an effective block at the doses of lidocaine used and further study is necessary to develop a useful block for surgical analgesia. Keywords analgesia, avian, birds, local anesthesia, nerve evoked muscle potentials, pain.
Brachial plexus blockade in Hispaniolan Amazon parrots AF da Cunha et al.
Introduction The blockade of sensory neurons of the brachial plexus has been investigated as a viable technique for providing analgesia for painful lesions of the wing in avian species (Figueiredo et al. 2008; Cardozo et al. 2009; Brenner et al. 2010), prevent pain during surgical treatments (Futema et al. 2002), and an adequate way to avoid central pain sensitization (Tryba 1998) and treat chronic pain (Mukherji et al. 2000). Furthermore, regional anesthesia can be used as a sole technique for anesthesia and analgesia in surgical procedures performed under sedation or light anesthesia and as a postoperative analgesic technique following invasive surgeries (Machin 2005). In avian medicine, brachial plexus blockade has been described in the chicken (Gallus gallus domesticus) (Figueiredo et al. 2008; Cardozo et al. 2009), mallard duck (Brenner et al. 2010) and, in a clinical case presentation, in the cockatiel (Nymphicus hollandicus), a free-ranging striped owl (Asio clamator) and in roadside hawks (Rupornis manirostris) (Vilani et al. 2006). Even though some anatomical and physiological differences are observed between avian and mammalian species, the basic pathophysiology of pain is comparable (Machin 2005). Taking these similarities into consideration, it is appropriate to suggest that brachial plexus blockade is a valuable technique for analgesia of the wings of avian species. An effective brachial plexus nerve block is achieved by injecting a local anesthetic close to the brachial plexus and subsequent diffusion of the drug into the perineural space (Neal et al. 2002; Campoy et al. 2010). However, the anatomic location of the brachial plexus varies greatly among avian species. In this sense a technique described for one species does not necessarily apply to other species. Several techniques have been described to ensure accurate needle placement during the nerve block in different species. Modern tools like ultrasonography have transformed the art of regional anesthesia into a science (Borgeat 2006). The advantages of using ultrasound to guide local anesthetic deposition include: 1) being able to see the needle tip relative to the nerve, artery and vein; 2) visually confirming injection of local anesthetic close to the nerve; and 3) preventing complications such as intra-fascial and intravascular injection of local anesthetic (Marhofer et al. 2005). As a result, ultrasound significantly enhances the effectiveness
of the brachial plexus block technique (Denny & Harrop-Griffiths 2005) and decreases adverse effects (Marhofer et al. 2005). To the authors’ knowledge, ultrasonography has not been described in avian species as a tool to guide brachial plexus blockade. The nerve evoked muscle potential (NEMP) is an electrophysiological technique for monitoring nerve function that makes it possible to assess and quantify the effectiveness of neural blockade by a local anesthetic (Pandin et al. 2006). Brachial plexus sensory nerve conduction velocity and somatosensory evoked potentials have been evaluated in Mallard ducks (Anas platyrhynchos) (Brenner et al. 2008, 2010), but the techniques are technically more challenging to perform, making them less useful clinically. NEMPs are a more useful method of assessing brachial plexus function and have not been previously used to evaluate local anesthesia in psittacine birds. The intent of this study was to compare palpation-guided and ultrasound-guided brachial plexus blockade with lidocaine in Hispaniolan Amazon parrots, examining the time-course of onset of local anesthesia, degree of the muscle relaxation, degree of nociception, and duration of muscle relaxation after brachial plexus blockade. It was hypothesized that the use of ultrasound-guided local anesthesia would improve the accuracy, decrease onset and increase the efficacy of the brachial plexus block. Materials and methods The study was approved by the Institutional Animal Care and Use Committee (IACUC) (Protocol No. 07061). Eighteen adult Hispaniolan Amazon parrots (Amazona ventralis) (mean weight 267 g; range 252–295 g) were obtained from a locally maintained colony. Tap water and food (Kaytee Exact Rainbow Pellets; Kaytee Inc, WI) were available ad libitum. Birds were considered to be healthy on the basis of a general physical examination. In all birds, anesthesia was induced with isoflurane (Isoflo; Abbott Laboratories, IL) in oxygen delivered by face mask. Each bird was intubated with an uncuffed endotracheal tube and connected to a Bain circuit with a flow rate of 200 mL kg)1 minute)1. All birds were positioned in dorsal recumbency on a circulating hot-water blanket (T/Pump; Gaymar industries Inc, NY) and a forced warm air electric cover blanket (Bair Hugger; Arizant Inc, MN), used to provide supplemental heat for the duration of the anesthetic period. Body
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temperature was maintained between 39 and 40 C [the reference interval for body temperature for birds is 39–43 C (West et al. 2007)]. Partial pressure of carbon dioxide in the expired end-tidal gas (PE¢CO2), arterial hemoglobin saturation with oxygen (pulse oximetry, SpO2), heart rate, esophageal temperature, respiratory rate, lead II electrocardiogram (ECG), partial pressure of isoflurane in the expired end-tidal gas (E¢Iso) and inspiratory fraction of oxygen (FiO2) were monitored with the use of a multi-function monitor (Datascope Passport 2; MAQUET, NJ). Once E¢Iso was stable at 1.5% for a minimum of 15 minutes, temperature was between 39 and 40 C and PE¢CO2, ECG, and SpO2 were considered normal, electromyography (EMG) and nerve stimulation electrodes were positioned (Sierra Wave electrodiagnostic system; Cadwell Laboratories, WA). A cathodal stimulating electrode, an insulated 26-gauge needle with insulation stripped from the tip (Uniplex UP, Pajunk Medical Technology, Germany), was inserted between the spinal cord and the brachial plexus near the cervical nerve root outlets, and the anodal electrode was placed subcutaneously within 1 cm of the cathodal electrode. The ground electrode was placed subcutaneously between the stimulating and recording electrodes to minimize stimulus artifact in the EMG recordings. The minimum threshold stimulus current sufficient to elicit a contraction in the distal muscle was recorded as a baseline. Subsequently, stimuli were applied at 1.5· the threshold current. EMGs were recorded between an insulated EMG electrode placed in the belly of a distal limb flexor muscle and a subcutaneous needle reference electrode located over the muscle belly (Fig. 1). Reduction of the muscle evoked potential amplitude following anesthetic injection was used to determine success or failure of the brachial plexus blockade. After instrumentation, baseline measurements were recorded. The birds were randomly assigned to two equal groups (nine birds per group) and received a single injection of 2 mg kg)1 of lidocaine (Xylocaine, AstraZeneca LP, DE) in a total volume of 0.3 mL in the brachial plexus area by either palpation or with the aid of ultrasonography. The injections were done aseptically using a 22-gauge, 3.8 cm insulated needle. In order to be consistent, a total volume of 0.3 mL was achieved by diluting 2 mg kg)1 of 2% lidocaine with 0.9%NaCl. For the palpation-guided group, the injection site was located by palpating the space between the pectoral muscle, 98
triceps and supracoracoideus aticimus muscle, the insertion of the tendons of the caudal coracobrachial muscle, and the caudal scapulohumeral muscle; the needle was inserted at the angle created by these muscles (Fig. 2). Prior to injection, the needle was aspirated in order to confirm that neither an air sac nor blood vessel had been perforated. For the ultrasound-guided group, birds were placed in dorsal recumbency, feathers were plucked in the brachial area caudal to the humerus, and the wing was extended. The brachial plexus and the adjacent vessels were located with B-mode ultrasonography using a 7–15 MHz linear probe or 8-5 MHz
Figure 1 Hispaniolan Amazon parrot with the right wing extended. The arrow represents the site of injection. Letters represent the positioning of the EMG electrodes where A is the recording electrode, B is the ground electrode and C is the anodal electrode. The copper alligator clip on the extended wing is an ECG lead.
Triceps m.
Caudal scapulohumeral m. Site of injection
Pectoral m.
Supracoracoideus aticimus m.
Caudal coracobrachial m.
Figure 2 Diagram of a Hispaniolan Amazon parrot with the right wing extended. The site of injection is the angle created by the pectoral, triceps and supracoracoideus aticimus muscles and the insertion of the tendons of the caudal coracobrachial and the caudal scapulohumeral muscles.
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Brachial plexus blockade in Hispaniolan Amazon parrots AF da Cunha et al.
convex transducer (iU22; Philips, WA). The linear high frequency transducer (7–15 MHz) was used to locate the brachial plexus and a second transducer, a lower frequency (8-5 MHz), lower resolution convex transducer, was used to visualize the injections. The transducer was placed caudally in the brachial area with the transducer head pointed to the contralateral shoulder (Fig. 3). After ultrasonographic identification of the neurovascular bundle (Fig. 4A), a 22-gauge, 3.8 cm insulated needle was inserted and advanced along the longitudinal axis of the ultrasound transducer with the entire shaft of the needle in the path of the beam (Fig. 4B). Lidocaine at a dose of 2 mg kg)1 was then injected into the space. All palpation-guided injections were performed by one investigator (AC), while the ultrasound-guided injections were performed by a second investigator (NR). The amplitudes of the NEMP were recorded prior to the brachial plexus injection at time zero, and at 5, 10, 15, and 20 minutes after injection. After time 20, anesthesia was discontinued and parrots were placed in padded cages for recovery. During recovery the wing position was observed and pinprick of the distal wing was attempted 20 minutes after full recovery. Degree of relaxation of both wings and response to pinprick was recorded. Full recovery was defined as the time at which the parrot was able to perch without imbalance. All EMG amplitudes for each subject were expressed as a percentage of the time 0, to permit comparison. Amplitudes were defined as the difference between onset (O) and peak of response (P) as observed at Figure 5. The NEMP results were analyzed statistically by a one way analysis of variance followed by the Holm-Sidak pairwise
Figure 3 Photograph of a Hispaniolan Amazon parrot in dorsal recumbency, showing the positioning of the ultrasound transducer caudal to the extended wing.
comparison procedure when p £ 0.05 using Sigma Plot 11. (SigmaPlot 11; Systat Software Inc, CA). Results A statistically significant difference in NEMP amplitudes was observed within the palpation-guided group when comparing time 0 to the times of 10, 15, and 20 minutes (Fig. 6). Times 5, 10, 15, and 20 differed significantly from time 0 for the ultrasoundguided group. No statistically significant difference in amplitudes was detected between the two groups at any time (Fig. 6), although amplitudes in the ultrasound-guided group were lower than palpation-guided group at all times after injection. No difference in motor function, muscle relaxation or wing droop was observed between blocked and non-blocked wings. Both techniques produced a dramatic decrease in the amplitude of nerve evoked
(a)
(b)
Figure 4 Gray-scale image of the brachial plexus area with the nerve bundle seen as a hypoechoic area and marked with an asterisk. (a) shows the air sac and is identified as a hyperechoic area with dirty shadowing (arrows). (b) shows the needle in place from caudal area (arrows).
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Neither self-injuries, nor intravenous or air sac injections were observed. The recoveries were unremarkable. Discussion
Figure 5 Example recordings of nerve evoked muscle potentials from an isoflurane anesthetized Hispaniolan Amazon parrot before and at 0, 5 10, 15, and 20 minutes after injection. Each tracing is a single wing muscle evoked potential by stimulation between the spinal cord and the brachial plexus.
Figure 6 Changes in mean ± SD % of nerve evoked muscle potential response amplitude in percentage, compared to time 0 for each bird. Data analyzed statistically by a one way analysis of variance followed by the Holm-Sidak pairwise comparison procedure (*p £ 0.05). The palpationguided group is represented by the line with filled circles and the ultrasound-guided block is represented by the line with open circles. Time 0 represents base line before local anesthesia injection and times 5, 10, 15, and 20 represent time in minutes after injection.
muscle potentials beginning 5 minutes after lidocaine injection (Fig. 6). Nociceptive assessment by pinprick in the distal wing of these parrots was unsuccessful, as the subjects resisted any human interaction preventing us from touching them. 100
In this study, nerve evoked muscle potentials were used as a nerve conduction monitoring tool to evaluate and compare the effectiveness of palpationguided or ultrasound-guided injection of local anesthetic for brachial plexus block in Hispaniolan Amazon parrots. Brachial plexus blockade has the potential to be useful as a regional anesthesia technique, allowing surgical procedures to be performed in the distal extremity of the wing if a reliable and easy to use technique can be developed. The results of the present study indicate a statistically significant decrease in NEMP amplitudes beginning 5 minutes after injection in the ultrasound-guided group and 10 minutes after the injection in the palpation-guided group with no differences among groups at any time point. Based on reduction of the nerve evoked muscle potential, a decrease in motor nerve conduction was observed and, although not measured, a decrease in sensory nerve conduction was assumed. After recovering from general anesthesia the expected muscle relaxation (wing droop) was not observed in any bird. The lack of wing droop in any of the birds of our study may have been due to using an inadequate dose of lidocaine. The effectiveness of a local anesthetic to produce neural blockade is proportional to the concentration and volume of local anesthetic used (Goodman et al. 2006; Stoelting & Hillier 2006). Higher doses of lidocaine have been reported for the brachial plexus block in birds. Brenner et al. (2010) observed inconsistent wing droop using 15 mg kg)1 of lidocaine with epinephrine in Mallard Ducks. Figueiredo et al. (2008) administered 20 mg kg)1 of lidocaine with epinephrine to chickens and observed wing droop in 12 out of 18 subjects (67% success rate). The safety of local anesthetics in birds is controversial because there are no published reports of their effects, especially cardiovascular effects, in any avian species. It is believed that birds are more sensitive than mammals to the cardiovascular effects of local anesthetics, especially small birds (Tranquilli et al. 2007; West et al. 2007), but this perception is based on a report in which budgerigars died after injection with lidocaine at a dose of 67 mg kg)1 (Grono 1961), a dose that would be toxic to any animal. In our
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Brachial plexus blockade in Hispaniolan Amazon parrots AF da Cunha et al.
study, the small body weight of the birds was considered a limiting factor, so for safety we chose a low dose of lidocaine. For consistency all injections were 0.3 mL per bird, and the lidocaine (2%) was diluted with saline; the final concentration of the injections ranged between 1.71 and 1.96 mg mL)1, depending on each bird’s body weight. However, the low concentration of the lidocaine may have been the cause of the lack of muscle relaxation and wing droop observed on recovery. Two possibilities might explain the lack of wing droop in our birds: (1) the low lidocaine concentration and volume may have incompletely blocked the A-beta nerve fibers, or (2) the block may have worn off very quickly. We suggest that the lack of muscle relaxation after the regional block may have some positive benefits as it could decrease the incidence of incoordination and self-injury in birds during recovery. In those studies describing brachial plexus block in birds, wing relaxation was used as an indicator of blockade success (Vilani et al. 2006; Cardozo et al. 2009). In our study, we did not observe wing relaxation following brachial plexus blockade, a finding that accords with the findings of Brenner et al. (2010) who also did not observe wing droop in all of the birds in that study. We believe that the decrease in NEMP after brachial plexus block observed in our study proves that lidocaine had an effect. One limitation of this study is related to the inability to test the sensory components of the block. Thus the results do not prove the full achievement of local anesthesia, and therefore the authors cannot recommend this technique for surgery. Several factors, such as body temperature, general anesthesia, intensity of the electrical stimulus, could add variability to the NEMP results (King & Rampil 1994). We undertook precautions to reduce their influence on the recordings: each bird’s temperature was monitored and maintained within the normal range (39–40 C); the intensity of the electrical stimulus was consistent from parrot to parrot; and isoflurane, the anesthetic of choice for NEMP studies because of its reportedly minimal effect on nerve conduction velocity (King & Rampil 1994; Oh et al. 2010) was used for general anesthesia. The use of ultrasonography to facilitate brachial plexus blocks with local anesthetic has been described previously in other species (Guntz et al. 2009; Campoy et al. 2010), and has been shown to improve the efficacy of the block because the operator can visualize the location of the needle relative to the nerves and the spread of local anesthetic around the
nerves; this reduces complications such as intravascular and intrathoracic injections of local anesthetic (Pandin et al. 2006). The goal of this project was to deposit the lidocaine as close as possible to the brachial plexus, without causing nerve damage, and anesthetize the wing. There was a statistically significant decrease in conduction amplitude between time zero and 5 minutes after injection in the ultrasound-guided group and between time zero and 10 minutes in the palpation-guided group. This difference might suggest a higher accuracy of placement of the drug near the brachial plexus when ultrasound was used, but the lack of statistical difference between groups suggest that similar efficacy between techniques was obtained. Our results agree with Marhofer et al. (2005) who suggested that ultrasonography is a useful tool, with potential to improve the positive outcome of local anesthesia. We add to their conclusions that ultrasonography should be used for loco-regional anesthesia to improve the accuracy of the block in species where the anatomy of the brachial plexus is not well defined in the literature. Furthermore, the amount of local anesthetics could be reduced without changing effectiveness of the sensory block by the aid of the ultrasonography (Marhofer et al. 1998), which is an important factor for small patients where small volumes of local anesthetics have to be used but we were unable to support this assertion with the current study. In this study two ultrasound transducers were used because it was difficult to inject the lidocaine using the linear transducer due to anatomic limitations of the region in these small birds. Linear transducers have better near field resolution, but because of the shape of the thorax and axilla the convex transducer was more appropriate for the injections. No complications such as intravenous injection, thoracic puncture or self-injury during recovery were observed during this study but should always be a concern. The prevention of these common complications was done by aspiration prior to injection to confirm that the needle was not introduced into the vasculature or into the clavicular air sacs, and by allowing recovery from anesthesia in padded cages. Conclusions This study has shown that injection of a dilute lidocaine solution in the region of the brachial plexus in Hispaniolan Amazon parrots has an effect
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on nerve conduction. The onset tended to be faster when using an ultrasound-guided technique but this was not statistically different from the palpation-guided technique. Neither technique, as described in this paper, achieved a complete block and further work needs to be carried out to develop a method that provides surgical analgesia.
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