Luis Campoy

Ultrasound-guided approach for axillary brachial plexus, femoral nerve, and sciatic nerve blocks in dogs

OBJECTIVE To describe an ultrasound-guided technique and the anatomical basis for three clinically useful nerve blocks in dogs. STUDY DESIGN Prospective experimental trial. ANIMALS Four hound-cross dogs aged 2 +/- 0 years (mean +/- SD) weighing 30 +/- 5 kg and four Beagles aged 2 +/- 0 years and weighing 8.5 +/- 0.5 kg. METHODS Axillary brachial plexus, femoral, and sciatic combined ultrasound/electrolocation-guided nerve blocks were performed sequentially and bilaterally using a lidocaine solution mixed with methylene blue. Sciatic nerve blocks were not performed in the hounds. After the blocks, the dogs were euthanatized and each relevant site dissected. RESULTS Axillary brachial plexus block Landmark blood vessels and the roots of the brachial plexus were identified by ultrasound in all eight dogs. Anatomical examination confirmed the relationship between the four ventral nerve roots (C6, C7, C8, and T1) and the axillary vessels. Three roots (C7, C8, and T1) were adequately stained bilaterally in all dogs. Femoral nerve block Landmark blood vessels (femoral artery and femoral vein), the femoral and saphenous nerves and the medial portion of the rectus femoris muscle were identified by ultrasound in all dogs. Anatomical examination confirmed the relationship between the femoral vessels, femoral nerve, and the rectus femoris muscle. The femoral nerves were adequately stained bilaterally in all dogs. Sciatic nerve block. Ultrasound landmarks (semimembranosus muscle, the fascia of the biceps femoris muscle and the sciatic nerve) could be identified in all of the dogs. In the four Beagles, anatomical examination confirmed the relationship between the biceps femoris muscle, the semimembranosus muscle, and the sciatic nerve. In the Beagles, all but one of the sciatic nerves were stained adequately. CONCLUSIONS AND CLINICAL RELEVANCE Ultrasound-guided needle insertion is an accurate method for depositing local anesthetic for axillary brachial plexus, femoral, and sciatic nerve blocks.

Distribution of a lidocaine-methylene blue solution staining in brachial plexus, lumbar plexus and sciatic nerve blocks in the dog

OBJECTIVE To determine the influence on the distribution of the volume of a local anaesthetic-methylene blue solution at three different nerve block sites in the dog. STUDY DESIGN Randomized, controlled, blinded experimental trial. ANIMALS 23 hound-cross dogs weighing 16-40 kg and aged 2 +/- 0 years (mean +/- SD). METHODS Dogs were anaesthetized and randomly assigned to three groups of seven or eight dogs each, based on volume administered: low, medium and high volume (L, M and H). Using electrolocation, the injection was performed after a positive response was elicited (flexion of the elbow for the brachial plexus block, quadriceps contractions for the lumbar plexus and dorsiflexion/plantar extension of the foot for the sciatic nerve block). At the brachial plexus site, groups L, M and H received 0.075, 0.15 and 0.3 mL kg(-1), respectively. At the lumbar plexus site, groups L, M and H received 0.1, 0.2 and 0.4 mL kg(-1), respectively. At the proximal sciatic nerve site, groups L, M and H received 0.05, 0.1 and 0.25 mL kg(-1), respectively. Necropsies were performed immediately following euthanasia. Staining of > or =2 cm along the nerve was considered sufficient; the proportions sufficient were compared with Fishers exact test. The volume was recommended when all the relevant nerves were stained sufficiently in all or all but one of the dogs within the group. RESULTS In the brachial plexus, only in group H were all the nerves stained sufficiently. In the lumbar plexus site, no statistical difference was found, but we suggest the H group volume to balance sufficient and excessive staining. At the sciatic nerve site, all volumes tested produced sufficient staining in all (or all but one) dogs. CONCLUSIONS AND CLINICAL RELEVANCE Volumes of 0.3 and 0.05 mL kg(-1) produced sufficient distribution for performing brachial plexus, and sciatic nerve blocks, respectively. Additionally, a volume of 0.4 mL kg(-1) might also be adequate for a lumbar plexus block (no statistical significance was reached).

Role of the hypoglossal nerve in equine nasopharyngeal stability

The equine upper airway is highly adapted to provide the extremely high oxygen demand associated with strenuous aerobic exercise in this species. The tongue musculature, innervated by the hypoglossal nerve, plays an important role in airway stability in humans who also have a highly adapted upper airway to allow speech. The role of the hypoglossal nerve in stabilizing the equine upper airway has not been established. Isolated tongues from eight mature horses were dissected to determine the distal anatomy and branching of the equine hypoglossal nerve. Using this information, a peripheral nerve location technique was used to perform bilateral block of the common trunk of the hypoglossal nerve in 10 horses. Each horse was subjected to two trials with bilateral hypoglossal nerve block and two control trials (unblocked). Upper airway stability at exercise was determined using videoendoscopy and measurement of tracheal and pharyngeal pressure. Three main nerve branches were identified, medial and lateral branches and a discrete branch that innervated the geniohyoid muscle alone. Bilateral hypoglossal block induced nasopharyngeal instability in 10/19 trials, and none of the control trials (0/18) resulted in instability (P<0.001). Mean treadmill speed (+/-SD) at the onset of instability was 10.8+/-2.5 m/s. Following its onset, nasopharyngeal instability persisted until the end of the treadmill test. This instability, induced by hypoglossal nerve block, produced an expiratory obstruction similar to that seen in a naturally occurring equine disease (dorsal displacement of the soft palate, DDSP) with reduced inspiratory and expiratory pharyngeal pressure and increased expiratory tracheal pressure. These data suggest that stability of the equine upper airway at exercise may be mediated through the hypoglossal nerve. Naturally occurring DDSP in the horse shares a number of anatomic similarities with obstructive sleep apnea. Study of species with extreme respiratory adaptation, such as the horse, may provide insight into respiratory functioning in humans.

Procedural sedation combined with locoregional anesthesia for orthopedic surgery of the pelvic limb in 10 dogs: case series

HISTORY Ten dogs weighing 36 (21.4-75) kg [median (min-max)] and aged 3 (1-9) years scheduled for orthopedic surgery involving the stifle and structures distal to it. PHYSICAL EXAMINATION Patients were classified as ASA I or II based on physical examination and basic hematology and biochemistry. MANAGEMENT Each dog was managed using combined femoral and sciatic nerve blocks and procedural sedation with an intravenous infusion of propofol (0.07-0.15 mg kg(-1) minute(-1)) and dexmedetomidine (1 μg kg(-1) hour(-1)). None of the patients required conversion to general anesthesia as a result of response to surgical stimulation. The level of sedation was considered adequate in all patients and was characterized by occasional head lifting, thoracic limb stretching, yawning, lingual movements and swallowing. The eye position ranged from central to partial ventromedial rotation and was accompanied by spontaneous blinking. Intra-operative cardiovascular and ventilatory variables were considered within acceptable limits. Muscle relaxation at the surgical field was adequate and surgical conditions were indistinguishable from those produced by general anesthesia. Intraoperatively, no additional analgesics were considered necessary. The quality of the recoveries was considered excellent in all cases. FOLLOW UP No additional pain relief was required in any of the dogs within the 10 hours following blockade. All dogs ate 5.5 (3.5-12) hours after recovery. Ambulation occurred at 4 (2-6) hours. No evidence of esophagitis or aspiration pneumonitis has been reported during a period of 1 year after the procedures in any of the dogs. CONCLUSION When combined with femoral and sciatic nerve blocks, procedural sedation has the potential of being an alternative to general anesthesia for orthopedic surgery involving the stifle and structures distal to it in the dog.

Comparison between acceleromyography and visual assessment of train‐of‐four for monitoring neuromuscular blockade in horses undergoing surgery

OBJECTIVE To compare acceleromyography (AMG) with visual assessment of train-of-four (TOF) for monitoring neuromuscular blockade and detecting residual muscle paralysis in horses receiving atracurium. STUDY DESIGN Prospective, controlled clinical study. ANIMALS Nine adult, client-owned horses weighing 577 (436, 727) kg (median, minimum, maximum) and ASA physical status I-II, admitted for surgery. METHODS An electrical nerve stimulator was used to stimulate the peroneal nerve with TOFs at 1 minute intervals. Before and after atracurium administration (0.15 mg kg(-1), IV), the number of twitches observed (TOF count, or TOFc) was assessed visually. When four twitches were seen (i.e., TOFc = 4) presence or absence of fade by visual assessment was recorded. Simultaneously, the response to each TOF was assessed by AMG; this measured TOFc, and twitch fade using TOF ratio (TOFR; ratio of fourth to first twitch). The anesthetist performing the visual evaluation was blinded to the AMG readings. Recovery from neuromuscular blockade was defined as the absence of fade by visual inspection or a TOFR > or =90% by AMG. RESULTS During onset of action of the drug, fade was first detected 4 (1, 8) minutes earlier by AMG (p = 0.008). Maximal blockade started at 6 (3, 17) minutes by visual assessment and 9 (3, 25) minutes by AMG (not significantly different). Only four horses achieved complete neuromuscular blockade (TOFc of zero by both methods); in those four horses AMG did not detect the start of the return of neuromuscular transmission before visual assessment. Visual assessment indicated the return of four twitches with no fade 12 (8, 42) minutes before AMG gave a TOFR of > or =90% (p = 0.004). CONCLUSION AND CLINICAL RELEVANCE There was no substantial advantage for AMG in detecting the onset of atracurium-induced neuromuscular blockade. However, AMG detected residual blockade when visual assessment of TOF did not. Application of AMG is likely to reduce the incidence of residual blockade.

Twitch potentiation: a potential source of error during neuromuscular monitoring with acceleromyography in anesthetized dogs

OBJECTIVE To measure twitch potentiation (the staircase phenomenon) in anesthetized dogs, and assess its relevance during neuromuscular monitoring with acceleromyography (AMG). STUDY DESIGN Randomized, prospective clinical trial. ANIMALS Sixteen dogs undergoing ovariohysterectomy. METHODS Under isoflurane anesthesia, neuromuscular function was monitored with train-of-four (TOF) stimuli every 15 seconds and quantified by AMG. Neuromuscular blockade (NMB) was produced with 0.15 mg kg(-1) atracurium IV. Dogs were randomly divided into two groups; a potentiation group (PG) in which TOF stimulation was applied for 20 minutes before atracurium was administered; and a control group (CG) where no such time was allowed. In both groups, the AMG was calibrated (at tCAL) just before atracurium was administered. TOF stimulation continued throughout the experiment in all dogs. The height of the first twitch (T(1)) (expressed as a fraction of T(1) at tCAL) and train-of-four ratio (TOFR) were recorded until TOFR returned to ≥90%. RESULTS In PG, T(1) increased significantly (p = 0.0078) from a median of 102% (range, 95, 109) at baseline to 118% (100, 142) at 20 minutes. In PG, no difference was found between T(1) at tCAL (immediately before atracurium administration) and T(1) when neuromuscular transmission returned (p = 0.42). In the CG, T(1) increased significantly between tCAL and the time neuromuscular transmission returned (p = 0.027). TOFR did not increase during twitch potentiation (all p = 0.32). CONCLUSIONS AND CLINICAL RELEVANCE T(1) increased significantly during 20 minutes of uninterrupted TOF stimulation in the absence of NMB, establishing that twitch potentiation occurs in anesthetized dogs. With no time for potentiation, T(1) increased during the course of recovery from NMB; this phenomenon introduces a bias in T(1) measurements and could affect studies reporting potency and duration of NMB based on T(1) or single twitches. TOFR was unaltered by potentiation emphasizing its clinical usefulness for excluding post-operative residual NMB.

Analgesic and gastrointestinal effects of epidural morphine in horses after laparoscopic cryptorchidectomy under general anesthesia

OBJECTIVE To evaluate the hypothesis that epidural morphine (0.1 mg kg(-1) ) decreases pain in horses after laparoscopic surgery without adversely affecting gastrointestinal (GI) motility. STUDY DESIGN Randomized clinical trial. ANIMALS Eighteen horses undergoing laparoscopic cryptorchidectomy under general anesthesia. METHODS Horses were randomly assigned to receive either epidural morphine (0.1 mg kg(-1) ) or no epidural before the start of surgery. Pain behaviors were assessed during the first two post-operative days using a numerical rating scale. Barium-filled spheres were administered through a nasogastric tube before anesthesia. GI motility was assessed by recording manure production, by quantitating the spheres in the manure, and by abdominal auscultation of intestinal sounds. Heart rates and cortisol concentrations were also measured during the post-operative period. RESULTS Pain scores increased for 12 hours after surgery in the control group and were significantly higher than in the morphine group for the first 6 hours. Pain scores remained unaltered in the morphine group throughout the observation period. Heart rate and plasma cortisol concentrations did not differ between groups or with time. No signs of colic were observed in any horse. CONCLUSION AND CLINICAL RELEVANCE Epidural morphine (0.1 mg kg(-1) ) did not adversely affect GI motility in horses after laparoscopic surgery under general anesthesia.

Observations of the potency and duration of vecuronium in isoflurane-anesthetized horses

OBJECTIVE To evaluate the potency and duration of three subparalyzing doses of vecuronium (VEC) in isoflurane-anesthetized horses. STUDY DESIGN Prospective experimental study. ANIMALS Thirteen healthy adult horses undergoing arthroscopic surgery. METHODS During isoflurane anesthesia, horses received one of three doses of vecuronium (25, 50, or 100 μg kg(-1)). Neuromuscular transmission was monitored with acceleromyography (AMG) with train-of-four (TOF) stimulation of the radial nerve. Maximal depression of the first twitch (T1), and onset time were recorded for each dose. Recovery time to a TOF ratio >90% was also evaluated. RESULTS Vecuronium 25 μg kg(-1) produced no observable T1 depression in four horses. VEC 50 μg kg(-1) (n = 5) produced a maximal T1 depression of [median (min, max)] 41 (20, 71) % in four horses, and no neuromuscular block was seen in the fifth. VEC 100 μg kg(-1) was given to four horses and produced a T1 depression of 73 (64, 78) %. Of the four horses in which VEC 50 μg kg(-1) produced a measurable neuromuscular block, three recovered spontaneously 43 (40, 52) minutes after VEC administration; a fourth subject received edrophonium to reverse residual block at the end of the surgery. Spontaneous recovery after VEC 100 μg kg(-1) occurred by 112 minutes in one horse, and had to be facilitated by edrophonium in the remaining three horses, more than 2 hours after VEC had been given. CONCLUSIONS AND CLINICAL RELEVANCE A dose of 100 μg kg(-1) VEC in isoflurane anesthetized horses failed to produce complete paralysis. The partial neuromuscular block lasted at least 2 hours after this dose had been administered. Edrophonium was required to reverse the neuromuscular block in three of four horses. It is likely that more than 100 μg kg(-1) VEC would be necessary for complete neuromuscular blockade in horses, and that this dose will last >2 hours.

Evaluation of oral maropitant as an antiemetic in cats receiving morphine and dexmedetomidine

Objectives The aim of the study was to evaluate the antiemetic effects of maropitant, after oral administration, in cats receiving morphine and dexmedetomidine. Methods This prospective, blinded, randomized controlled trial involved 98 healthy female domestic shorthair cats. Cats were randomly assigned to receive maropitant PO 8 mg total (group M) administered 18 h prior to sedation with intramuscular dexmedetomidine 20 µg/kg and morphine 0.1 mg/kg, or no antiemetic treatment (group C). The occurrence of signs of nausea (sialorrhea and lip-licking), retching and emesis during the 30 mins following administration of dexmedetomidine and morphine was measured for each group. Results Two cats were excluded from the investigation. Cats in group M (n = 46) received an average of 2.5 mg/kg of maropitant PO. Compared with group C (n = 50), cats in group M had lower incidences of emesis (M: 4% vs C: 40%), retching (M: 8% vs C: 40%) and lip-licking (M: 30% vs C: 52%) (all P <0.05). The incidence of sialorrhea was not different between groups (M: 21% vs C: 22%). Conclusions and relevance Maropitant 8 mg total PO was effective in reducing morphine and dexmedetomidine-induced emesis by 10-fold, when administered as early as 18 h in advance to healthy cats. Maropitant PO could be useful for administration the evening prior to a scheduled procedure requiring sedation/anesthesia to decrease the incidence of emesis.

The sensitivity of sheep to vecuronium: an example of the limitations of extrapolation

To the Editor, In the absence of species-specific data and despite the obvious pitfalls, it is common practice for investigators to extrapolate pharmacokinetic and pharmacodynamic information between species. Although sheep are used frequently as a model for research projects, there is a paucity of pharmacological information for many drugs in this species. Our empiric observations suggest that the potency of vecuronium in sheep may be much greater than that in humans. This study measures the potency of vecuronium in sheep under general anesthesia. Following Cornell University Institutional Animal Care and Use Committee approval, fifteen healthy adult female sheep (52–69 kg) were anesthetized for experimental stifle surgery, the results of which are to be published elsewhere. After sedation with intravenous midazolam and morphine, anesthesia was induced with propofol and maintained with isoflurane in oxygen. Neuromuscular monitoring was carried out with acceleromyography (TOF-Watch SX, Organon, Dublin, Ireland), similarly to a previous description in the dog. Train-of-four stimulation was applied to the ulnar nerve every 15 sec (60 mA, 0.2 msec), with the acceleration-sensitive crystal taped to the manus. After baseline stabilization and calibration, a dose of vecuronium (4, 6, or 8 lg kg, randomly allocated) was administered and T1 depression was measured. The averages of three consecutive values at baseline and at maximal depression were used for analysis. The effective doses for 50% and 95% T1 depression (ED50 and ED95) were calculated by the log-dose/logit method as described previously. The mean ED50 (standard deviation [SD]) and mean ED95 (SD) were 3.5 (1.2) lg kg and 13.2 (3.8) lg kg, respectively. The slope of the log-dose/logit linear regression was 2.22. Twitch depression after vecuronium and onset times are presented in the Table. Considering that the ED50 and ED95 of vecuronium in humans are approximately 30 and 45 lg kg, respectively, sheep are substantially more sensitive than humans. Although morphological differences between muscles have been identified to account for unequal responses to vecuronium within a species, further study is needed amongst species to identify the mechanisms responsible for the differences in sensitivity to a given neuromuscular blocking agent (NMBA). There are limitations to this study. First, the study involved a modest number of animals. A recent investigation suggests that at least 24 subjects should be recruited. Second, vecuronium 6 lg kg and 8 lg kg had similar effects (Table). This could be explained by direct muscle stimulation in the presence of complete neuromuscular block; however, this is unlikely considering the pulse duration used (0.2 msec). Furthermore, in pilot studies using this preparation, larger doses ([ 12 lg kg) abolished twitch height completely. It is also possible that the normal variation between subjects combined with a small sample size resulted in the effects of these two doses being indistinguishable. Of importance, the slope for the log-dose/logit relation in these sheep was only 2.22. In humans, the slopes for the log-dose/logit curves of a number of NMBAs approximate 4.5. It is not known whether this is a real difference between species or an artifact created by the small sample size. This question could be answered by collecting data M. Martin-Flores, MV (&) M. D. Pare, DVM L. Campoy, LV R. D. Gleed, BVSc College of Veterinary Medicine, Cornell University, Ithaca, NY, USA e-mail: mm459@cornell.edu