Use of electrical nerve stimulation to monitor lumbosacral epidural needle placement in cats

ObjectiveTo determine the minimal electrical threshold (MET) necessary to elicit muscle contraction of the pelvic limb or tail when an insulated needle is positioned outside (MET_out) and inside (MET_in) the lumbosacral epidural space in cats.Study designProspective, blinded study.AnimalsTwelve mixed-breed healthy adult cats, scheduled for a therapeutic procedure where lumbosacral epidural administration was indicated.MethodsUnder general anesthesia, an insulated needle was advanced through tissues of the lumbosacral interspace until its tip was thought to be just dorsal to the interarcuate ligament. An increasing electrical current (0.1 ms, 2 Hz) was applied through the stimulating needle in order to determine the MET necessary to obtain a muscle contraction of the pelvic limb or tail (MET_out), and then 0.05 mL kg^?1 of iohexol was injected. The needle was further advanced until its tip was thought to be in the epidural space. The MET was determined again (MET_in) and 0.2 mL kg^?1 of iohexol was injected. The cats were maintained in sternal position. Contrast medium spread was determined through lateral radiographic projections.ResultsThe radiographic study confirmed the correct needle placement dorsal to the interarcuate ligament in all cats. When the needle was placed ventrally to the interarcuate ligament, iohexol was injected epidurally in ten and intrathecally in two cats. The MET_out and MET_in was 1.76 ± 0.34 mA and 0.34 ± 0.07 mA, respectively (p < 0.0001).Conclusion and clinical relevanceNerve stimulation can be employed as a tool to determine penetration of the interarcuate ligament but not the piercing of the dura mater at the lumbosacral space in cats.     

The use of a nerve stimulation test to confirm sacrococcygeal epidural needle placement in cats

ObjectiveTo determine if a nerve stimulation test (NST) could act as a monitoring technique to confirm sacrococcygeal epidural needle placement in cats.Study designProspective experimental trial in a clinical setting.AnimalsTwenty-four adult cats, scheduled for a therapeutic procedure where epidural anesthesia was indicated.MethodsUnder general anesthesia, an insulated needle was inserted through the S₃-Cd₁ intervertebral space guided by the application of a fixed electrical current (0.7 mA) until a motor response was obtained. The NST was considered positive when the epidural nerve stimulation produced a motor response of the muscles of the tail, whereas it was considered negative when no motor response was evoked. In the NST positive cases, 0.3 mL kg⁻¹ of 0.5% bupivacaine was administrated before needle withdrawal. Ten minutes after injection, epidural blockade was confirmed by the loss of perineal (anal), and pelvic limbs reflexes (patellar and withdrawal).ResultsThe use of a fixed electrical stimulation current of 0.7 mA resulted in correct prediction of sacrococcygeal epidural injection, corroborated by post bupivacaine loss of perineal and pelvic limb reflexes, in 95.8% of the cases.Conclusion and clinical relevanceThis study demonstrates the feasibility of using, in a clinical setting, an electrical stimulation test as an objective and in real-time method to confirm sacrococcygeal epidural needle placement in cats.     

Use of electrical stimulation to monitor lumbosacral epidural and intrathecal needle placement in rabbits

Objective-To determine the minimal electric threshold of neurostimulation dorsally and ventrally to the interarcuate ligament in the lumbosacral area necessary to cause muscle contraction of the hind limb or tail and determine whether a continuous electrical stimulation applied to an insulated needle during lumbosacral epidural needle placement could be used to distinguish the epidural from the intrathecal space in rabbits. Animals-24 New Zealand white rabbits. Procedures-Rabbits received iohexol (0.2 mL/kg) either dorsally (group 1) or ventrally to the interarcuate ligament in the lumbosacral area (groups 2 and 3). Correct placement of the needle was determined by use of the loss of resistance to injection technique (group 2) or a continuous electrical stimulation (group 3) and confirmed by examination of the iohexol distribution pattern on radiographs. Results-In all rabbits of group 1, iohexol was injected in the lumbosacral area, outside the epidural space. In groups 2 and 3, iohexol was injected intrathecally. No pure iohexol epidural migration of iohexol was observed. Mean ± SD minimal electric threshold to elicit a motor response was 1.2 ± 0.3 mA, 0.3 ± 0.1 mA, and 0.3 ± 0.1 mA in groups 1, 2, and 3, respectively. Conclusions and Clinical Relevance-Neurostimulation was a useful technique to determine correct intrathecal needle placement in rabbits but failed to detect the lumbosacral epidural space when the common technique, used in dogs and cats for the lumbosacral epidural approach, was used.     

Identification of the sacrococcygeal epidural space using the nerve stimulation test or the running-drip method in dogs

ObjectiveTo compare the nerve stimulation test (group NS) with the running-drip method (group RUN) for successful identification of the sacrococcygeal (SCo) epidural space prior to drug administration in dogs.AnimalsA total of 62 dogs.Study designA randomized clinical study.MethodsDogs requiring an epidural anaesthetic as part of the multimodal anaesthetic plan were randomly allocated to one of the two study groups. In group NS, the epidural space was located using an insulated needle connected to a nerve stimulator; in group RUN, the epidural space was identified using a Tuohy needle connected to a fluid bag elevated 60 cm above the spine via an administration set. The success of the technique was assessed 5 minutes after epidural injection by the disappearance of the patella reflex. Data were checked for normality, nonparametric data was analysed using a Mann–Whitney U test and success rate was analysed using a Fisher’s exact test. The significance level was set at p < 0.05, and the results are presented in absolute values, percentage (95% confident interval) and median (range).ResultsThe success in identification of the epidural space did not differ between groups NS and RUN [87.1% (70.2%–96.4%) versus 90.3% (74.2%–98%); p = 1.000]. The time required for identification of the epidural space was shorter in group RUN [26 (15–53) seconds] than in group NS [40 (19–137) seconds] (p = 0.0225). No other differences were found in any studied variables.Conclusionand clinical relevance In this study, both RUN and NS techniques were successful in identifying the epidural space at the SCo intervertebral space. RUN requires no specialised equipment, can be performed rapidly and offers an alternative to the NS for use in general veterinary practice.     

Evaluation of repetitive nerve stimulation in young dogs

Evaluation of neuromuscular transmission requires a complete electrodiagnostic evaluation including repetitive nerve stimulation. Supra-maximal stimulation of the peroneal nerve and recording of the compound muscle action potentials from the cranial tibial muscle were under-taken in 25 young dogs of two to 18 months of age. Proximal stimulation in the trochanteric fossa and distal stimulation in the popliteal fossa were chosen for small and large breeds, respectively. Highly consistent results were obtained when the examined muscle was kept at a constant temperature and the limb was firmly fixed. Neither sex- (14 females, 11 males) nor age- related (mean = 4·4 months] differences in neuromuscular transmission were found, but frequency-dependent phenomena were observed. These became more distinct with high frequency stimulation. Pseudofacilitation (n = 16/15 Hz; n = 7/50 Hz), was found to range within certain limits (6 to 26 per cent/15 Hz; 13 to 31 per cent/50 Hz). Its mean values at 50 Hz stimulation were apparently higher (26·88 per cent) than those at 15 Hz stimulation (11·3 per cent). Decremental responses occurred mainly with application of tetanic stimulation frequency (n = 1/15 Hz; n = 12/50 Hz) and may represent blocking of neuromuscular transmission. Each of these reaction patterns usually started to occur at the fourth potential of a series (81 per cent/15 Hz; 94 per cent/50 Hz) and remained constant during the second half of the stimulation train in most cases. The occurrence of post-tetanic phenomena in healthy dogs is poorly understood. Post-tetanic potentiation observed in the present material (24 per cent) may represent pseudofacilitation following high stimulation frequency (50 Hz/100 pulses).     

Electrical stimulation of lumbar spinal nerve roots in dogs

The aim of this study was to test the applicability of electrical stimulation of lumbar spinal nerve roots and obtain normative electrical root stimulation (ERS) data for L7 nerve root and sciatic nerve in dogs. For that purpose ERS and sciatic nerve stimulations were performed consecutively, in totally 40 healthy dogs. ERS was applied in the L7/S1 intervertebral space via monopolar needle electrodes. Muscle responses were recorded from the gastrocnemius muscles on the left and right hind limbs. Sciatic nerve stimulation was performed at the greater trochanter level on the left hind limb, with records obtained from the left gastrocnemius muscle. Mean root latencies of the left and right side were 5.22?±?0.49 ms and 5.29?±?0.53 ms, respectively. There was no significant difference in root latency between the right and left sides. The mean terminal latency was 3.82?±?0.46 ms. The proximal motor nerve conduction velocity of the sciatic nerve was 63.15?±?3.43 m/s. The results of this study show that ERS provides objective data about the integrity of lumbar spinal nerve roots by evaluating the entire population of motor fibres and total length of the motor axon in dogs. ERS can be considered a useful diagnostic method for confirmation of diagnoses of lumbosacral diseases.     

Evaluation of electrical nerve stimulation for epidural catheter positioning in the dog

ObjectiveTo evaluate the accuracy of epidural catheter placement at different levels of the spinal cord guided solely by electrical nerve stimulation and resultant segmental muscle contraction.Study designProspective, experiment.AnimalsSix male and two female Beagles, age (1 ± 0.17 years) and weight (12.9 ± 1.1 kg).MethodsAnimals were anesthetized with propofol and maintained with isoflurane. An insulated epidural needle was used to reach the lumbosacral epidural space. A Tsui epidural catheter was inserted and connected to a nerve stimulator (1.0 mA, 0.1 ms, 2 Hz) to assess positioning of the tip at specific spinal cord segments. The catheter was advanced to three different levels of the spinal cord: lumbar (L2–L5), thoracic (T5–T10) and cervical (C4–C6). Subcutaneous needles were previously placed at these spinal levels and the catheter was advanced to match the needle location, guided only by corresponding muscle contractions. Catheter position was verified by fluoroscopy. If catheter tip and needle were at the same vertebral body a score of zero was assigned. When catheter tip was cranial or caudal to the needle, positive or negative numbers, respectively, corresponding to the number of vertebrae between them, were assigned. The mean and standard deviation of the number of vertebrae between catheter tip and needle were calculated to assess accuracy. Results are given as mean ± SD.ResultsThe catheter position in relation to the needle was within 0.3 ± 2.0 vertebral bodies. Positive predictive values (PPV) were 57%, 83% and 71% for lumbar, thoracic and cervical regions respectively. Overall PPV was 70%. No significant difference in PPV among regions was found.Conclusion and clinical relevancePlacement of an epidural catheter at specific spinal levels using electrical nerve stimulation was feasible without radiographic assistance in dogs. Two vertebral bodies difference from the target site may be clinically acceptable when performing segmental epidural regional anesthesia.     

The normal response to repetitive motor nerve stimulation in dogs

The responses of certain muscles to stimulation at different frequencies has been studied in normal dogs. Repetitive stimulation at 10 and 20 Hz resulted in a smooth, progressive decremental response when the compound muscle action potential (CMAP) was recorded from the plantar, and to a lesser extent the palmar, interosseous muscles. In contrast, there was a slight incremental response when the CMAP was recorded from the cranial tibial muscle. Studies using a competitive neuromuscular blocking agent have suggested that the plantar interosseous muscles have a greater proportion of low efficacy synapses in comparison with the other muscles studied. The cranial tibial muscle may therefore be more suitable for assessing neuromuscular transmission than the distal limb muscles.     

Cortical averaged evoked potentials produced by pudendal nerve stimulation in dogs

Averaged evoked potentials were recorded from the scalp of 22 dogs after repetitive stimulation of the pudendal nerve. Four experimental procedures were used: (1) percutaneous needle-stimulating electrodes with dogs tranquilized with xylazine; (2) percutaneous needle-stimulating electrodes with dogs tranquilized with acepromazine; (3) percutaneous needle-stimulating electrodes with dogs anesthetized with alpha-chloralose; and (4) Sherrington type stimulating electrodes applied directly to nerves with dogs anesthetized with alpha-chloralose. The average evoked potentials were similar with all treatments. Three peaks (N1, P1, and N2) with consistent latency and amplitude were generally present, followed by additional peaks with variable latencies and amplitudes. The mean latency for N1 after direct stimulation was significantly longer than the mean latency for N1 in the 3 other groups (95% confidence intervals). There were no other significant differences in mean latencies among groups for any of the peaks.     

The use of electrical stimulation to guide epidural and intrathecal needle advancement at the L5‐L6 intervertebral space in dogs

ObjectiveTo determine the minimal electrical threshold (MET) necessary to elicit appropriate muscle contraction when the tip of an insulated needle is positioned epidurally or intrathecally at the L_5-6 intervertebral space (phase-I) and to determine whether the application of a fixed electrical current during its advancement could indicate needle entry into the intrathecal space (phase-II) in dogs.Study designProspective, blinded study.AnimalsThirteen (phase-I) and seventeen (phase-II) dogs, scheduled for a surgical procedure where L_5-6 intrathecal administration was indicated.MethodsUnder general anesthesia, an insulated needle was first inserted into the L_5-6 epidural space and secondly into the intrathecal space and the MET necessary to obtain a muscular contraction of the pelvic limb or tail at each site was determined (phase-I). Under similar conditions, in dogs of phase-II an insulated needle was inserted through the L_5-6 intervertebral space guided by the use of a fixed electrical current (0.8 mA) until muscular contraction of the pelvic limb or tail was obtained. Intrathecal needle placement was confirmed by either free flow of cerebrospinal fluid (CSF) or myelography.ResultsThe current required to elicit a motor response was significantly lower (p < 0.0001) when the tip of the needle was in the intrathecal space (0.48 ± 0.10 mA) than when it was located epidurally (2.56 ± 0.57). The use of a fixed electrical stimulation current of 0.8 mA resulted in correct prediction of intrathecal injection, corroborated by either free flow of CSF (n = 12) or iohexol distribution pattern (n = 5), in 100% of the cases.Conclusion and clinical relevanceNerve stimulation may be employed as a tool to distinguish epidural from intrathecal insulated needle position at the L_5-6 intervertebral space in dogs. This study demonstrates the feasibility of using an electrical stimulation test to confirm intrathecal needle position in dogs.     

Influence of electrical stimulation on regeneration of the radial nerve in dogs

The effects of biphasic electric fields on nerve regeneration that follows injury to the left radial nerve were studied in dogs by electromyography (EMG). Left and right radial nerves were crushed with a serrated haemostat. Stimulating electrodes were positioned proximally and distally to the site of the injury. The left nerves received rectangular, biphasic and current pulses (30 microA, 0.5 Hz) through the injury for two months. The right radial nerves were treated as controls and regenerated without electrical stimulation. EMG activities were recorded intramuscularly from the left and right musculus extensor digitalis communis (MEDC). Results obtained at the end of the two-month stimulation period showed a significant difference in EMG activity between the left (stimulated) and the right (non-stimulated) MEDC, suggesting that electrical treatment enhanced nerve regeneration.     

犬的硬膜外麻醉

麻醉效果的好坏直接影响到相应的手术及其操作的成败。本文通过对硬膜外麻醉机理、犬脊椎解剖结构、硬膜外麻醉药物的介绍,对临床上硬膜外麻醉的适用情况、药物选择进行介绍。     

Effects of epidural xylazine on EEG responses to surgical stimulation during isoflurane anaesthesia in dogs

The effects of epidural administration of 250 μg/kg xylazine on EEG responses to surgical stimulation of 5 different intensities were evaluated during isoflurane anaesthesia for an experimental orthopaedic procedure in dogs. The dogs were assigned randomly to one of 2 treatment groups receiving either xylazine (n = 4) or equal volumes of sterile water (n = 4) (control group) epidurally. Intense surgical stimulation during removal of a bone graft from the dorsoiliac spine of the ileum was associated with a significantly (P = 0.0339) higher increase in EEG alpha/delta ratio after epidural administration of sterile water than after epidural injection of 250 μg/kg of xylazine. In addition, the preincision baseline values for 80% spectral edge frequency were significantly (P = 0.0339) lower in the xylazine group compared to control dogs. Our results suggest that epidural administration of 250 μg/kg of xylazine during orthopaedic procedures in dogs exerts antinociceptive effects which may be in part mediated by a supraspinal effect of xylazine.     

Ultrasound-guided fine needle aspiration in the diagnosis of peripheral nerve sheath tumors in 4 dogs

Ultrasound-guided fine needle aspiration was used in establishing the diagnosis in 4 cases of malignant peripheral nerve sheath tumor. Sonographic and cytologic characteristics are discussed. Because of its availability and ease of use, axillary ultrasonography with fine needle aspiration can be an initial diagnostic step for suspected brachial plexus tumors.     

Use of vagal nerve stimulation as a treatment for refractory epilepsy in dogs

OBJECTIVE: To evaluate safety and efficacy of vagal nerve stimulation in dogs with refractory epilepsy. DESIGN: Placebo-controlled, double-masked, crossover study. ANIMALS: 10 dogs with poorly controlled seizures. PROCEDURE: A programmable pacemaker-like device designed to deliver intermittent stimulation to the left cervical trunk of the vagus was surgically implanted in each dog. Dogs were assigned randomly to two 13-week test periods, 1 with nerve stimulation and 1 without nerve stimulation. Owners recorded data on seizure frequency, duration, and intensity, as well as adverse effects. RESULTS: No significant difference in seizure frequency, duration, or severity was detected between overall 13-week treatment and control periods. During the final 4 weeks of the treatment period, a significant decrease in mean seizure frequency (34.4%) was detected, compared with the control period. Complications included transient bradycardia, asystole, and apnea during intraoperative device testing, and seroma formation, subcutaneous migration of the generator, and transient Horner's syndrome during the 14-day period between surgery and suture removal. No adverse effects of stimulation were detected, and most owners were satisfied with the treatment. CONCLUSIONS AND CLINICAL RELEVANCE: Vagal nerve stimulation is a potentially safe approach to seizure control that appears to be efficacious in certain dogs and should be considered a possible treatment option when antiepileptic medications are ineffective.     

Spinal epidural empyema in seven dogs

OBJECTIVE: To characterize the clinical signs, diagnostic and surgical findings, and outcome in dogs with spinal epidural empyema (SEE). STUDY DESIGN: Retrospective study. ANIMALS: Seven dogs. METHODS: Dogs with SEE between 1992 and 2001 were identified from a computerized medical record system. Inclusion criteria were: neurologic examination, vertebral column radiographs, myelography, antimicrobial culture and susceptibility of material collected surgically from the vertebral canal, a definitive diagnosis of SEE confirmed by surgery, and microscopic examination of tissue from the vertebral canal. RESULTS: Common signs were lethargy, fever, anorexia, apparent spinal pain, and paraparesis/plegia. Common laboratory abnormalities were peripheral neutrophilia, and neutrophilic pleocytosis in cerebrospinal fluid (CSF). Three dogs had concurrent discospondylitis and 1 of these had vertebral luxation. On myelography, extradural spinal cord compression was focal (2 dogs), multifocal (3), or diffuse (2). Bacteria were isolated not from CSF but from blood, surgical site, pleural fluid, or urine in 6 dogs. Dogs were administered antibiotics and had surgical decompression by hemilaminectomy. Five dogs improved neurologically and had a good long-term outcome. Two dogs were euthanatized, 1 because of worsening of neurologic signs and pneumonia, and the other because of herniation of a cervical intervertebral disc 1 month postoperatively, unrelated to the SEE. CONCLUSION: Dogs with SEE may have a good outcome when treated by surgical decompression and antibiotic administration. CLINICAL RELEVANCE: SEE should be included in a list of possible causes for dogs with fever, apparent spinal pain, and myelopathy.     

Maturation of spinal-evoked potentials to tibial and ulnar nerve stimulation in clinically normal dogs

Spinal-evoked potentials were recorded from 2 litters of clinically normal mixed-breed dogs between 35 and 300 days of age. Summated responses to tibial nerve stimulation were recorded from percutaneous needle electrodes placed at L7-S1, L4-5, T13-L1, C7-T1, and the cisterna cerebellomedullaris. The ulnar nerve was stimulated with recordings at C7-T1 and the cisterna cerebellomedullaris. Amplitudes did not change significantly with age, but were significantly (P less than 0.05) different between various recording sites. On day 35, segmental and overall (L7-cisterna cerebellomedullaris) conduction velocities were less than half of the adult values. Spinal cord conduction velocities increased with age, reaching adult values at approximately 9 months of age. It was determined that quadratic equations best predicted the conduction velocities during maturation.     

Electrical nerve stimulation as an aid to the placement of a brachial plexus block

Most local anaesthetic blocks are placed blindly, based on a sound knowledge of anatomy. Very often the relationship between the site of deposition of local anaesthetic and the nerve to be blocked is unknown. Large motor neurons may be stimulated with the aid of an electrical current. By observing for muscle twitches, through electrical stimulation of the nerve, a needle can be positioned extremely close to the nerve. The accuracy of local anaesthetic blocks can be improved by this technique. By using the lowest possible current a needle could be positioned with in 2-5 mm of a nerve. The correct duration of stimulation ensures that stimulation of sensory nerves does not occur The use of electrical nerve stimulation in veterinary medicine is a novel technique that requires further evaluation.     

Cardiovascular effects of epidural blocks in dogs

Cardiovascular and respiratory function was studied after epidural injection of lignocaine hydrochloride (3 mg kg¹) at the lumbosacral space in dogs premedicated with methadone (0–8 mg kg¹), acepromazine (0.3 mg kg¹) and atropine (0.6 to 1.2 mg). Analgesia was produced caudal to the third to fifth thoracic dermatomes; there was no significant change in cardiovascular function, respiratory rate, arterial blood pH or blood gas tensions. Relaxation of the hind leg and abdominal muscles was profound and haemorrhage caused a rapid fall in arterial blood pressure accompanied by tachycardia.