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Combined paravertebral plexus block and parasacral sciatic block in healthy dogs.

OBJECTIVE To evaluate the effectiveness of paravertebral lumbar plexus block combined with parasacral sciatic block to anesthetize one hind limb in awake dogs. STUDY DESIGN Randomized, controlled, blinded experimental study. ANIMALS Eight healthy mongrel dogs weighing 12.4 ± 4.5 kg and aged 7 ± 2.33 years. METHODS After sedation with medetomidine, dogs received B1: bupivacaine 0.25%, 0.2 mL kg(-1), B2: bupivacaine 0.5%, 0.2 mL kg(-1) , B3: bupivacaine 0.25% 0.4 mL kg(-1), P1: NaCl 0.2 mL kg(-1), P2: NaCl 0.4 mL kg(-1) . The lumbosacral plexus was blocked through a paravertebral block of the fourth, fifth and sixth lumbar nerves combined with a parasacral block. The relevant nerves were located using a nerve stimulator and injections of each treatment were administered. Degree and durations of sensory blockade were determined through the response to a Halsted clamp pressure on the skin innervated by the saphenous/femoral and lateral cutaneous femoral nerves (lumbar dermatomes) and by the peroneal and tibial nerves. The degree and duration of motor blockade was assessed evaluating the ability to walk normally and proprioception. RESULTS P1 and P2 treatments did not show any grade of sensory or motor blockade. The B2 treatment produced a higher degree of sensory blockade compared to B1 and B3 for both lumbar and sciatic dermatomes. There was no significant difference in the degree of sensory blockade comparing B1 to B3. The B2 treatment had greater motor blockade compared to B1 and B3. The duration of sensory and motor blockade was longer in B2 compared to B1 and B3. CONCLUSION AND CLINICAL RELEVANCE When the nerve stimulator is used to perform the lumbosacral plexus block, the concentration of the bupivacaine has a more important role than the volume to produce a more solid and longer block.

Femoral nerve block: a novel psoas compartment lateral pre-iliac approach in dogs.

OBJECTIVE To describe a new approach to block the femoral nerve and to evaluate the distribution of a dye injected into the psoas compartment using a new femoral nerve block approach; to assess its clinical application, when combined with a sciatic nerve block, for surgical anaesthesia/analgesia of the pelvic limb in dogs. STUDY DESIGN Prospective anatomical, research and clinical study. ANIMALS Two dog cadavers; two dogs that had to be euthanized for reasons unrelated to this study, and 15 dogs undergoing pelvic limb orthopaedic surgery. METHODS Phase 1: anatomical dissections were performed to determine a simple method to approach the femoral nerve within the psoas compartment. Phase 2: 0.1 mL kg(-1) of a lidocaine-new methylene blue solution was injected bilaterally after successful electrolocation of the femoral nerve in two anaesthetized dogs. Colorant spread was evaluated through femoral nerve dissections after euthanasia. Phase 3: in 15 dogs undergoing pelvic limb orthopaedic surgery under light general anaesthesia with isoflurane, intra-operative analgesic effect (cardiovascular responses) and early post-operative pain score, of the novel femoral nerve block combined with a sciatic nerve block as the sole analgesic protocol, were evaluated. RESULTS Phase 1: a needle inserted from the lateral aspect of the lumbar muscles, cranially to the iliac crest and with a 30-45° caudo-medial direction, reaches the femoral nerve in the caudal portion of the psoas compartment. Phase 2: Four femoral nerves were stained >2 cm. Phase 3: this novel lateral pre-iliac approach, combined with the sciatic nerve block, blunted the intra-operative cardiovascular response to surgical stimulation in 13 out of 15 anaesthetized dogs. In addition, rescue analgesia was not required in the early post-operative 2-hour period. CONCLUSION AND CLINICAL RELEVANCE The lateral pre-iliac femoral nerve block technique may provide adequate intra- and early post-operative pain relief in dogs undergoing pelvic limb surgery.

Stress-related biomarkers in dogs administered regional anaesthesia or fentanyl for analgesia during stifle surgery.

OBJECTIVES To compare the effects of regional anaesthesia and opioid administration on adrenocortical and glycaemic responses, postoperative pain and recovery quality in dogs undergoing stifle surgery. STUDY DESIGN Prospective, blinded clinical study. ANIMALS Forty-five dogs anaesthetized for tibial tuberosity advancement or tibial plateau levelling osteotomy, and 15 healthy dogs undergoing non-invasive orthopaedic diagnostic procedures. METHODS The baseline behaviour of each dog was classified on a descriptive scale before anaesthesia. Dogs were anaesthetized using a standard protocol. Those undergoing surgery were randomly assigned to one of three intraoperative analgesia protocols: 1) peripheral (femoral and sciatic) nerve block (bupivacaine 0.5%; 0.15 mL kg(-1) in each nerve; group PNB); 2) spinal anaesthesia (isobaric bupivacaine 0.5%; 0.05 mL kg(-1); group SPI); and 3) intravenous fentanyl variable rate infusion and postoperative methadone (0.2 mg kg(-1); group FEN). Blood samples were collected for measurement of cortisol and glucose concentrations on arrival (TAR), at induction (TIND), at tracheal extubation (TEXT), and 1 hour post-extubation (TPEX). After extubation, a researcher unaware of the dogs group assignment evaluated pain and recovery quality using the Glasgow Composite Measure Pain Scale (Short-Form) and a descriptive scale, respectively. RESULTS Median recovery quality was significantly worse in group FEN (p < 0.0001) compared with all other groups. Postoperative pain scores were lower in group PNB compared with groups SPI and FEN. Cortisol and glucose concentrations increased significantly from TAR at TEXT and TPEX (p < 0.0001) in group FEN, and were unchanged from TAR in the other groups. CONCLUSIONS AND CLINICAL RELEVANCE Analgesia with a peripheral nerve block or spinal anaesthesia prevented the glycaemic and cortisol responses to surgery, promoted better recovery quality, and decreased postoperative pain scores compared with FEN. In the present study, the regional anaesthesia techniques used were found to be excellent alternatives to fentanyl administration.

Peripheral nerve stimulation under ultrasonographic control to determine the needle-to-nerve relationship

OBJECTIVE To determine the needle-to-nerve distances during electrical nerve location in dogs at different currents and pulse duration using a peripheral nerve stimulator (PNS) under ultrasound control (US), and the minimal electrical thresholds (MET) necessary to obtain a motor response (MR) after achieving needle-to-nerve contact. STUDY DESIGN Prospective in vivo experimental trial in a clinical setting ANIMALS Thirty dogs, scheduled for locoregional anaesthesia of the sciatic nerve. METHODS Needle-to-nerve distance was measured ultrasonographically after obtaining the MR of sciatic nerve with 2, 1 and 0.5 mA and pulse duration 0.1 ms (NS0.1). Thereafter the needle was placed in contact with the nerve and MET was determined. The procedure was repeated with 0.3 ms (NS0.3). Finally the needle was reintroduced to contact the sciatic nerve guided only by US, thus MET-US was determined. Data were analysed using Kruskal-Wallis or Mann-Whitney tests. RESULTS Needle-to-nerve distances were greater when MR was obtained with 2 mA than with 1 and 0.5 mA at 0.1 and 0.3 ms. No significant differences were observed between the needle-to-nerve distances using 0.1 or 0.3 ms. The MET [median (range)] was 0.4 (0.18-1.3) mA in NS0.1, 0.32 (0.12-0.8) mA in NS0.3; while MET-US was 0.7 (0.32-1.5) mA. When the needle contacted the nerve, the MR achieved with currents below 0.3 mA was obtained in 17.2, 40 and 0% of cases using NS0.1, NS0.3 and US respectively. CONCLUSIONS AND CLINICAL RELEVANCE The electrical current necessary to obtain a MR decreased as the needle moved towards the nerve. However when the needle tip contacted the nerve, an MR with low current intensity could not be obtained. Thus the absence of motor response at currents below 0.3 mA cannot rule out needle-epineurium contact. When ultrasound is combined with PNS, it is more important to assess the correct needle position than searching for an MR at low currents.

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.

Anatomical and radiological study of the thoracic paravertebral space in dogs: iohexol distribution pattern and use of the nerve stimulator.

OBJECTIVE To describe the landmarks and methodology to approach the thoracic paravertebral space in dogs; to evaluate if intercostal muscular response could be evoked by a nerve-stimulator; to radiographically assess the distribution pattern of a radio-opaque contrast medium after thoracic paravertebral injections. STUDY DESIGN Randomized, controlled, experimental trial. ANIMALS Two mongrel dog cadavers (anatomical study) and 24 mongrel dogs (experimental study). METHODS For the anatomic study 0.2 mL kg(-1) of new methylene blue (NMB) was injected at the 5th thoracic paravertebral space; for the experimental study dogs were divided into three groups and received 1 (T(5)), 2 (T(4) and T(6)) or 4 (T(4), T(5), T(6) and T(7)) paravertebral injections of iohexol. The paravertebral approach was performed with insulated needles using landmarks and a blind technique. When the needle tip reached the respective thoracic paravertebral space, the nerve-stimulator was switched-on and the presence/absence of intercostal muscular twitch was registered, thus a total volume of 0.2 mL kg(-1) of iohexol, divided into equal parts for each injection point, was administered. Radiological studies were performed with two orthogonal projections at different times. Positive injection was confirmed when the paravertebral space was occupied by iohexol in both projections. RESULTS NMB was distributed in the T(5) paraverterbal space. In the experimental study, when the needle tip reached the respective paravertebral space, intercostal twitching was obtained in 80% of the total injections with a stimulating current of 0.5 mA. The incidence of positive cases when the intercostal twitch was obtained with 0.5 mA was 83.3%. The main distribution pattern observed was cloud like without longitudinal diffusion. CONCLUSION AND CLINICAL RELEVANCE Intercostal muscular responses obtained with a stimulating current of 0.5 mA could be useful to locate thoracic spinal nerves in dogs and in our study the injected solution was confined to one thoracic paravertebral space.

Ultrasound-guided thoracic paravertebral injection in dogs: a cadaveric study

OBJECTIVE To describe ultrasound-visualized anatomy and the spread characteristics of a dye injected in the thoracic paravertebral (TPV) space under ultrasound guidance. STUDY DESIGN Anatomic cadaver study. ANIMALS Seven dog cadavers. METHODS One cadaver was used to observe, identify, and describe the relevant TPV anatomy. In the remaining six, the left fifth TPV space was randomly assigned to be injected with either a low volume (LV; 0.05 mL kg-1) or high volume (HV; 0.15 mL kg-1) of dye. Subsequently, the contralateral side was injected with the alternative volume. Anatomic dissections were conducted to determine the incidence of complete spinal nerve staining (>1 cm circumferential coverage), number of contiguous spinal nerves dyed and the absence or presence of solution in particular locations. RESULTS The ultrasound-visualized anatomy of the TPV space was defined as the intercostal space abaxial to the vertebral body, delimited by the parietal pleura ventrally and the internal intercostal membrane dorsally. The endothoracic fascia divides the paravertebral space into dorsal and ventral compartments. The target nerve was completely dyed in five of six and six of six injections in the LV and HV conditions, respectively. In one LV injection, the nerve was partially dyed. No multisegmental spread affecting contiguous spinal nerves was found in either treatment. Multisegmental spread was found in the ventral compartment of the TPV space, affecting the sympathetic trunk on 3 (0-3) and 3.5 (1-6) vertebral spinal levels in the LV and HV conditions, respectively, but differences between volumes were not significant. No intrapleural, ventral mediastinal or epidural migration was observed. CONCLUSIONS AND CLINICAL RELEVANCE Ultrasound-guided TPV block is a potentially reliable technique. The LV appeared sufficient to dye a single spinal nerve and multiple sympathetic trunk vertebral levels. Multiple TPV injections may be needed to provide adequate thoracic analgesia in dogs undergoing thoracic surgery.

Hypoventilation exacerbates the cardiovascular depression caused by a high volume of lumbosacral epidural bupivacaine in two isoflurane‐anesthetized dogs

This letter reports the cardiopulmonary changes resulting from lumbosacral epidural administration of bupivacaine (0.25%, 0.6 mL kg ) in isofluraneanesthetized dogs. Anesthesia was induced in two healthy, adult, mixed-breed male dogs (A and B) weighing 19.5 kg and 16.3 kg, respectively, with 5% isoflurane (Crist alia Produtos Qu ımicos Farmacêuticos Ltda, SP, Brazil) in oxygen (5 L minute ) administered by facemask. After endotracheal intubation, anesthesia was maintained at an end-tidal isoflurane concentration (FE0Iso) of 1.0 minimum alveolar concentration, previously determined for each dog (1.51% and 1.65%), and inspiratory fraction of oxygen (FIO2) of approximately 98% delivered from a circle breathing system with the dogs breathing spontaneously. With the dogs in lateral recumbency, a 20 gauge cephalic vein catheter and a 22 gauge dorsal pedal artery catheter (Nipro Medical Ltda, SP, Brazil) were placed to facilitate the infusion of lactated Ringer’s solution (3 mL kg 1 hour ) and to measure arterial blood pressure. An 8 Fr catheter introducer (Arrow International, Inc., PA, USA) was placed in the right jugular vein and a 7 Fr pulmonary artery (PA) catheter (Edwards Lifesciences LLC, CA, USA) was introduced. The placement of the tip of the catheter in the PA was confirmed according to the typical pressure waveforms displayed on the monitor (DX 2021; Philips Healthcare, Netherlands). All pressure transducers were calibrated using a mercury manometer and zeroed at the level of the manubrium. Cardiac output (CO) was measured by injection of 5 mL of cold saline solution (0–5 °C). An electrical heating pad was used to maintain body temperature, monitored by the PA thermistor, at 37.5–38.5 °C. The cardiac index (CI), systemic vascular resistance index (SVRI) and stroke volume index (SI) were calculated by normalizing CO and systemic vascular resistance to body surface area and stroke volume to body weight. Heart rate (HR), respiratory frequency (fR), end-tidal carbon dioxide tension (PE0CO2), FE0Iso and FIO2 were measured using a multi-channel monitor (Digicare Biomedical Technology, Inc., FL, USA). Tidal volume (VT) was measured by the ventilator’s pneumotachometer and minute ventilation (V̇E) was calculated as VT 9 fR. After instrumentation (197 and 182 minutes for dogs A and B, respectively), the dogs were placed in sternal recumbency and the lumbosacral area was aseptically prepared. An 18 gauge Tuohy needle (Becton Dickinson & Co., NJ, USA) was introduced in the lumbosacral space; placement in the epidural space was confirmed by the loss of resistance technique and the absence of blood and cerebrospinal fluid at the hub of the needle. Epidural administration of bupivacaine (Crist alia Produtos Qu ımicos Farmacêuticos Ltda) was performed over 2 minutes and cardiopulmonary variables were recorded at 0 (baseline), 5, 15, 30, 60 and 90 minutes. In comparison with baseline values, VT, fR and V̇E decreased, whereas PE0CO2 increased in both dogs at 15 minutes. HR decreased in dog A and MAP, CI and SVRI decreased in both dogs (Table 1). The recommended volume of local anesthetic solution to be injected into the lumbosacral epidural space in dogs is 0.2 mL kg 1 (Torske & Dyson 2000). Higher volumes up to 0.6 mL kg 1 have been investigated as alternatives to extend analgesia more cranially (Freire et al. 2010). In the present study, thoracic spread of epidural bupivacaine seemed to affect intercostal, abdominal and possibly diaphragmatic muscular function, resulting in hypoventilation, which, in the presence of a high sympathetic block, may lead to pronounced cardiovascular depression (Shibata

Regional anesthetic techniques for the thoracic limb and thorax in small animals: A review of the literature and technique description

Veterinary regional anesthesia (RA) has been rapidly increasing in popularity over the last 10 years, as evidenced by the increasing amount of literature available and the continuous development of new techniques in small animals. The introduction of new technologies such as nerve stimulation and ultrasound (which increased the objectivity and precision of the procedure) and the promising beneficial perioperative effects conferred by RA are encouraging clinicians to incorporate these techniques in their daily perioperative anesthetic and analgesic animal care. However, there is a lack of consensus regarding outcomes when RA is used, as well as outcome comparisons between regional anesthetic techniques. Further large-scale clinical studies are still necessary. This article is the first part of a two-part review of RA in small animals, and its aim is to discuss the most relevant studies in the veterinary literature, where objective methods of nerve location have been used, and to illustrate in pictures the currently used techniques for providing RA to the thoracic limb and the thorax in small animals.

Regional anesthetic techniques for the pelvic limb and abdominal wall in small animals: A review of the literature and technique description

Increasing interest in using peripheral nerve blocks in small animals is evident, given the numerous studies published recently on this topic in important veterinary journals. Initially, research was focused on intraoperative analgesia to the pelvic limb, and several descriptions of lumbosacral plexus, femoral and sciatic nerve blocks have been described in studies. There is recent interest in developing techniques for somatosensory blockade of the abdominal wall. This article is the second part of a two-part review of regional anesthesia (RA) in small animals, and its aim is to discuss the most relevant studies in the veterinary literature, where objective methods of nerve location have been used, and to illustrate in pictures the currently used techniques for providing RA to the abdominal wall and the pelvic limb in small animals.