Neuromuscular blocking effects of cisatracurium and its antagonism with neostigmine in a canine model of autosomal-recessive centronuclear myopathy.

BACKGROUND: Centronuclear myopathy (CNM) is a rare congenital condition associated with skeletal muscle weakness. Patients with CNM may have decreased acetylcholine receptor expression and a reduced number of releasable quanta. Such perturbations could affect the time-course of neuromuscular blocking agents (NMBAs) and their antagonism with cholinesterase inhibitors. As a result of the rarity of CNM, prospective data regarding NMBA use in this subpopulation is scarce. We evaluated the neuromuscular blocking effects of cisatracurium and its antagonism with neostigmine in a canine model of CNM. METHODS: Six dogs with congenital autosomal-recessive CNM and six controls received cisatracurium 0.15 mg kg(-1) i.v. under general anaesthesia and intermittent positive pressure ventilation. Neuromuscular function was monitored with acceleromyography.When the second response (T2) to train-of-four (TOF) stimulation returned, neostigmine 0.04 mg kg(-1) (with glycopyrrolate) were administered i.v. The onset time, time to spontaneous return of T2, and the time to reach a TOF ratio ≥0.9 after neostigmine administration were recorded. RESULTS: Onset time was no different between groups. Median (interquartile range) time to return of T2 was 27 (24-31) min for control dogs and 26 (22-31) min for CNM dogs (P=0.93).After neostigmine administration, a TOF ratio ≥0.9 was reached in 12 (10-15) min and 17 (16-19) min in control and CNM, respectively (P=0.005). CONCLUSIONS: The spontaneous return of T2 was not different between groups. However, neostigmine-facilitated recovery was significantly slower in dogs with CNM. Canine autosomal-recessive CNM does not preclude the use of cisatracurium or its antagonism with neostigmine.

TOF-Watch(R) monitor: failure to calculate the train-of-four ratio in the absence of baseline calibration in anaesthetized dogs.

BACKGROUND: TOF-Watch(®) monitors are designed to display train-of-four (TOF) count when neuromuscular block is intense, and to display TOF ratio when it is less intense. In dogs recovering from non-depolarizing neuromuscular block, when all four twitches are easily visible and apparently of similar magnitude, TOF-Watch(®) monitors often display TOF counts and not TOF ratios, as would be expected. We have never encountered this problem when the monitor was calibrated before neuromuscular blocking agent administration. METHODS: Fourteen healthy female dogs undergoing ovariohysterectomy were investigated. Recovery from neuromuscular block was assessed with a calibrated TOF-Watch SX(®) monitor. When the TOF ratio returned to 90%, the TOF-Watch SX(®) was replaced with an uncalibrated TOF-Watch(®) monitor. The output obtained from the uncalibrated TOF-Watch(®) was compared with that of the calibrated device. RESULTS: The median TOF ratio measured by the calibrated TOF-Watch SX(®) unit at recovery was 91 (86-100)% (n=14). The uncalibrated TOF-Watch(®) monitor displayed TOF counts in six dogs [2 (0, 4)] and TOF ratios in the remaining eight dogs [91 (79, 98)%], that is, the uncalibrated device failed to display appropriately >40% of the time. CONCLUSIONS: TOF-Watch(®) monitors must be calibrated before neuromuscular blocking agents are administered to dogs. When these devices are not so calibrated, they default to a reference value for twitch magnitude that was defined in healthy adult people. Even though neuromuscular transmission was restored in these dogs, we surmise that they did not achieve the default reference value, causing the monitor to display TOF counts rather than TOF ratios.

Unilateral cervical plexus block for prosthetic laryngoplasty in the standing horse.

BACKGROUND: Locoregional anaesthetic techniques can facilitate certain surgeries being performed under standing procedural sedation. The second and third spinal cervical nerves (C2, C3) are part of the cervical plexus and provide sensory innervation to the peri-laryngeal structures in people; block of these nerves might permit laryngeal lateralisation surgery in horses. OBJECTIVES: To describe the anatomical basis for an ultrasound-guided cervical plexus block in horses. To compare this block with conventional local anaesthetic tissue infiltration in horses undergoing standing prosthetic laryngoplasty. STUDY DESIGN: Cadaveric study followed by a double-blinded prospective clinical trial. METHODS: A fresh equine cadaver was dissected to characterise the distribution of C2 and C3 to the perilaryngeal structures on the left side. A second cadaver was utilised to correlate ultrasound images with the previously identified structures; a tissue marker was injected to confirm the feasibility of an ultrasound-guided approach to the cervical plexus. In the clinical study, horses were assigned to two groups, CP (n = 17; cervical plexus block) and INF (n = 17; conventional tissue infiltration). Data collection and analyses included time to completion of surgical procedure, sedation time, surgical field conditions and surgeon's perception of block quality. RESULTS: We confirmed that C2 and C3 provided innervation to the perilaryngeal structures. The nerve root of C2 was identified ultrasonographically located between the longus capitis and the cleidomastoideus muscles, caudal to the parotid gland. The CP group was deemed to provide better (P<0.0002) surgical conditions with no differences in the other variables measured. MAIN LIMITATIONS: Further studies with larger numbers of horses may be necessary to detect smaller differences in surgical procedure completion time based on the improved surgical filed conditions. CONCLUSIONS: For standing unilateral laryngeal surgery, a cervical plexus block is a viable alternative to tissue infiltration and it improves the surgical field conditions.

Use of 3D printer technology to facilitate surgical correction of a complex vascular anomaly with esophageal entrapment in a dog.

A 10 week old female intact Staffordshire terrier was presented with a total of five congenital cardio-thoracic vascular anomalies consisting of a patent ductus arteriosus (PDA) with an aneurysmic dilation, pulmonic stenosis, persistent right aortic arch, aberrant left subclavian artery and persistent left cranial vena cava. These abnormalities were identified with a combination of echocardiogram and computed tomography angiography (CTA). The abnormalities were associated with esophageal entrapment, regurgitation, and volume overload of the left heart with left atrial and ventricular enlargement. A 2 cm diameter aneurysmic dilation at the junction of the PDA, right aortic arch and aberrant left subclavian artery presented an unusual surgical challenge and precluded simple circumferential ligation and transection of the structure. A full scale three dimensional model of the heart and vasculature was constructed from the CTA and plasma sterilized. The model was used preoperatively to facilitate surgical planning and enhance intraoperative communication and coordination between the surgical and anesthesia teams. Intraoperatively the model facilitated spatial orientation, atraumatic vascular dissection, instrument sizing and positioning. A thoracoabdominal stapler was used to close the PDA aneurysm prior to transection. At the four-month postoperative follow-up the patient was doing well. This is the first reported application of new imaging and modeling technology to enhance surgical planning when approaching correction of complex cardiovascular anomalies in a dog.

Development of a peripheral nerve stimulator-guided technique for equine pudendal nerve blockade.

The aim of this study was to develop and evaluate a procedure for equine pudendal nerve block using a peripheral nerve locator. In the first experiment, six ponies were used to determine the relationship between elicited muscle contractions (anal, perineal or both) and nerves serving the perineal region (pudendal, caudorectal and perineal nerves) when methylene blue dye was injected using the electrolocation technique. This experiment showed that the pudendal nerve was approached effectively when both anal and perineal twitch were elicited during electrolocation. In a second experiment, seven Thoroughbred horses were used to evaluate the appropriate volume of anaesthetic solution for the nerve block. Immediately after euthanasia, lidocaine/methylene blue solution was injected after positive electrolocation. A stained segment of 2 cm or more of the nerve was considered effective and this was evaluated after dissection. Both 10 and 20 mL per injection site resulted in effective nerve staining. Finally, pudendal nerve block was performed and evaluated in 27 horses admitted for selected reproductive surgical procedures including perineoplasty, urethroplasty, clitorectomy in mares and penile examination, phallectomy and urethrostomy in geldings. Surgical time varied from several minutes to 3 h. The choice between lidocaine, mepivacaine or bupivacaine was based on the duration of analgesia required. In mares and males, a volume of 20 mL and 10 mL, respectively, was injected per site. The use of a peripheral nerve stimulator-guided pudendal nerve block is a feasible, safe and reliable alternative for both epidural and general anaesthesia, to provide peri-operative analgesia in clinical equine patients undergoing specific reproductive surgeries.

Magnetic resonance imaging in the diagnosis and surgical management of sacral osteochondrosis in a mastiff dog.

The clinical, radiographic, magnetic resonance imaging (MRI), surgical and pathological findings related to an osteochondral lesion of the sacrum in a mastiff dog are described. The dog showed chronic signs of pain in its pelvic limbs. Radiography revealed a triangular mineralised opacity at the craniodorsal aspect of the sacrum consistent with sacral osteochondrosis. A T2-weighted spin-echo MRI revealed dorsal and lateral compression of the cauda equina. The osteochondral fragment was removed via a dorsal laminectomy, and the clinical signs resolved. Histological abnormalities in the fragment were consistent with a diagnosis of osteochondrosis.

Kinking of endotracheal tubes during maxima flexion of the atlanto-occipital joint in dogs.

Endotracheal tubes manufactured from red rubber and polyvinyl chloride (PVC) were compared, using radiographic techniques, in dog cadavers, under in vitro conditions and in anaesthetised dogs (in vivo study). All endotracheal tubes were radiographed in 'neutral' and flexed positions and the percentage reduction in the ventrodorsal radiographical diameter of the tube was calculated. The red rubber tubes kinked completely in 40 per cent of the cadavers, 75 per cent of the in vitro study and 40 per cent of anaesthetised dogs. The PVC tubes kinked completely in only one case (in vivo study). However, these tubes had a mean reduction in diameter of 15 per cent in the dog cadaver study, 19 per cent in the in vitro study and 26 per cent in the in vivo study. During procedures in which the trachea is intubated and the atlanto-occipital joint of the patient must be flexed, PVC endotracheal tubes may be less prone to kinking than red rubber tubes.