A novel extraoral ultrasound-guided approach for mandibular nerve block in Rahmani sheep.

BACKGROUND: Regional anesthesia is the favored choice in ruminant animals compared to general anesthesia, primarily due to its high safety margin and reduced demand for cost-intensive equipment in addition to its field applicability. Ultrasound-guided nerve block has gained significant attention in the field of veterinary medicine. This study utilized twenty-seven sheep of the native Rahmani breed to both demonstrate and evaluate the effectiveness of the ultrasound guided inferior alveolar nerve block technique. METHODS: The research comprised three phases: Phase 1 involved an anatomical examination of mandibles and sheep heads to locate the mandibular foramen and delineate the mandibular nerve course. Phase 2 included ultrasound-guided injection of methylene blue dye at specific sites along the mandibular nerve in cadaveric sheep heads. In Phase 3, clinical implementation of ultrasound-guided inferior alveolar nerve blocks was conducted in 27 live sheep, assessing efficacy, onset, and duration. RESULTS: Vertical extraoral ultrasound-guided nerve block was achieved successfully in 25 sheep (98%). A preliminary cadaveric study showed good distribution of the injectate at the mandibular nerve site. The mean onset time was 138 ± 18 s, and the mean duration time was 54 ± 4.1 min. Prominent analgesia of the ipsilateral mandible, medial surface of the cheek, and lateral border of the tongue was observed. CONCLUSIONS: Ultrasound-guided mandibular nerve block holds promise as a technique for providing effective and safe anesthesia in sheep undergoing mandibular procedures.

Introducing a novel intraoral mandibular nerve block technique for loco-regional analgesia in camels (Camelus dromedarius): a cadaveric study using computed tomography.

The aim of this study was to introduce a novel intraoral technique for performing mandibular nerve blocks in dromedary camels (Camelus dromedarius). In this study, 18 adult camel skulls of varying ages and breeds were examined to determine the position of the mandibular foramen. Using a Vernier caliper, three dimensions in millimeters were measured: (1) the distance between the mandibular foramen (MF) and the caudal edge of the third molar tooth at the occlusal surface level, (2) the distance between the MF and the rostral edge border of the mandible's ramus (RER) at the occlusal surface level, and (3) the distance between the MF and the ventral margin border of the mandible (VM). The technique was evaluated using five intact camel cadaver heads (n = 5), and a total of ten mandibular nerve blocks were described. An 18-gauge 80-mm Tuohy needle was inserted into the mouth commissure and advanced caudally while injecting a saline-methylene blue solution. The accuracy of the injection was confirmed through the infiltration of the contrast dye into the target area using computed tomography (CT) and post procedural dissection. Anatomical study of the mandibular nerve site was performed to aid the blind insertion of the needle. The findings contribute to the development of veterinary anesthesia techniques and provide anatomical considerations for clinicians performing oral surgeries in sedated camels. The results demonstrated the successful implementation of the intraoral technique, highlighting its efficacy and reliability in achieving local anesthesia for oral surgeries involving the lower jaw and teeth in sedated camels. Further research studies are needed to evaluate the long-term efficacy and safety of the technique and to compare it with existing approaches.

Evaluation of frontal and infratrochlear nerve blocks for standing sedated frontonasal sinusotomy in horses.

OBJECTIVE: To determine if targeted blocking of frontal and infratrochlear nerves provided anesthesia for the approach to a frontonasal sinusotomy. STUDY DESIGN: Two part study: Part 1 randomized crossover design; Part 2 proof of concept. ANIMALS: N = 12; six each in Parts 1 and 2. METHODS: Part 1: Each horse had either frontal and infratrochlear nerve blocks or a line block performed with 2% mepivacaine hydrochloride. Mechanical nociceptive thresholds (MNT) were obtained at five sites along a proposed frontonasal sinusotomy prior to injection, and at 10, 60, and 120 min after blocking. After a 4 day washout period, the opposite procedure was performed. Order of procedure and side of face were randomized. MNTs were analyzed using mixed-model ANOVA with p < .05. Part 2: Frontal and infratrochlear nerve blocks were performed followed by creation of a skin/periosteal incision, which was closed at 2 h. Ability to create and suture the incision, and the size of the incision were recorded. RESULTS: For part 1, both line and targeted blocks resulted in at least two times an increase in median MNT values at each of the five sites, as compared to baseline MNT values (p < .0025). In Part 2, incisions could be completed in five of six horses, with median incision size of 6.5 × 5 cm. CONCLUSION: Following frontal and infratrochlear nerve blocks, MNTs were increased along a proposed frontonasal sinusotomy, and skin incisions could be created in the majority of horses. CLINICAL SIGNIFICANCE: Frontal and infratrochlear nerve blocks provide an alternative technique to create a frontonasal sinusotomy.

Evaluation of the addition of adrenaline in a bilateral maxillary nerve block to reduce hemorrhage in dogs undergoing sharp staphylectomy for brachycephalic obstructive airway syndrome. A prospective, randomized study.

OBJECTIVE: To assess the use of adrenaline (0.00198%) in a bilateral maxillary nerve block to reduce intraoperative hemorrhage in dogs undergoing staphylectomy for the treatment of brachycephalic obstructive airway syndrome (BOAS). STUDY DESIGN: Prospective, randomized, double-blinded controlled study. SAMPLE POPULATION: A total of 32 client owned, clinically affected dogs undergoing a cut and sew sharp staphylectomy for treatment of BOAS. A total of 16 dogs randomly assigned to adrenaline (A) group and 16 to no-adrenaline (NA) group. METHODS: A bilateral maxillary nerve block was performed in all dogs prior to staphylectomy using lidocaine alone (group NA) or a combination of lidocaine and adrenaline (group A). Total hemorrhage was measured by weighing cotton-tipped applicators and swabs used on precision scales. In addition, a semi-quantitative hemorrhage score (1-5) was determined. Dogs were monitored for intraoperative hemodynamic stability during the procedure. RESULTS: Total hemorrhage was significantly (p = .013) lower in group A compared with group NA. The median semi-quantitative hemorrhage score was significantly lower for group A (p = .029) compared with group NA. No significant adverse effects were noted due to adrenaline usage. CONCLUSION: This study demonstrated that the use of adrenaline in a bilateral maxillary nerve block results in significantly lower intraoperative hemorrhage during cut and sew sharp staphylectomy and appeared safe to use. CLINICAL SIGNIFICANCE: Potential clinical advantages include improved visualization, prevention of unnecessary blood loss and reduction in risk of blood aspiration.

Image analysis comparison of nerve staining with food dye, methylene blue or tissue marker.

OBJECTIVE: Novel locoregional techniques use dye studies to confirm successful nerve targeting. The goal was to objectively quantify and compare nerve staining characteristics of dye mixtures commonly reported in the literature using image analysis software. STUDY DESIGN: Prospective, randomized cadaveric study. METHODS: Thirty-six brachial plexus nerves from unpreserved pig cadavers were randomized into three groups of 12: FD (1:10 mixture of blue food dye and bupivacaine 0.5%), MB (methylene blue 1%) and TM (0.1:10 mixture of blue tissue marker and lidocaine 2%). Nerves were immersed in dye for 1, 15, 30 or 60 minutes (n = 3 each). Images of nerves before immersion (baseline) and at each time point with epineurium intact (superficial staining) and after longitudinal bisection (deep staining) were processed using image analysis software. Color saturation values were divided into quartiles (dark, medium-dark, medium-light or light). Percentage of stained nerve area in each quartile was calculated and compared using two-way anova. RESULTS: Superficially, at minute 1, dark saturation covered 40% of nerve area in FD versus 19% in MB (p = 0.04) and 0% in TM (p < 0.0001). In bisected nerves, dark and medium-dark saturations occurred only in FD; medium-light saturation comprised anywhere from 4% to 22.5% over time in FD versus <1% at any time in MB (p = 1.000; p = 0.343; p = 0.383; p = 0.262). Deep staining was not found in TM at any point. CONCLUSION AND CLINICAL RELEVANCE: Food dye rapidly stains superficial and deep nerve layers. Based on these characteristics, investigators can choose the appropriate dye for their study.

Investigation of a maxillary nerve block technique in guinea pigs (Cavia porcellus): A cadaveric study comparing two injectate volumes.

OBJECTIVE: To investigate and describe an extraoral approach to perform a maxillary nerve block in guinea pigs. STUDY DESIGN: Prospective, randomized, blinded, descriptive, cadaveric study. ANIMALS: A total of 14 adult guinea pig cadavers. METHODS: Two cadavers were used for anatomic dissection and determination of maxillary nerve block approach. A maxillary nerve block via infraorbital approach was then performed in 12 cadavers. A low volume (0.1 mL) or high volume (0.2 mL) of diluted methylene blue injectate was randomly assigned to the right or left side, with the other volume used for the contralateral side. The maxillary nerve was dissected after each injection by an investigator blinded to injectate volume. The region of dye distribution was identified, and the degree of staining assigned an accuracy score (0-2). Nerve coverage was considered adequate if ≥6 mm of circumferential staining was present. RESULTS: Accuracy evaluation indicated successful dye deposition in 10/12 [2 (0-2), median (range)] injections in the low volume group and 8/12 [2 (1-2)] injections in the high volume group. The majority (79.2%) of injections resulted in adequate nerve staining. There were no statistically significant differences between injectate volumes for accuracy (p = 0.64) or adequacy (p > 0.99) of staining. CONCLUSIONS: The infraorbital approach is a simple and practical method for maxillary nerve blockade in guinea pigs. An injectate volume of 0.1 mL results in adequate maxillary nerve coverage; however, additional studies are needed to assess the efficacy in clinical use.

Ultrasound-guided and 'blind' sciatic nerve injection techniques: Comparison in rat cadavers.

OBJECTIVE: To compare the success rate and extent of sciatic nerve staining with a bupivacaine-dye solution using two injection techniques: 'blind' or ultrasound-guided approach. STUDY DESIGN: Prospective, experimental, randomized, cadaveric study. ANIMALS: Adult female Wistar rat cadavers [n = 24, mass 352 g (323-374)]. METHODS: Each sciatic nerve was randomly allocated to one of two groups: 'blind' (group B) or ultrasound-guided approach (group US) to injection. Following injection of bupivacaine-dye solution (0.1 mL), gross anatomical dissection was performed to visualize nerve staining, categorizing it as either positive or negative. The length of nerve staining was then measured and visual inspection conducted to identify potential nerve damage. Fisher's exact test was used to compare positive or negative nerve staining, and the Wilcoxon signed rank test used to compare the length of nerve staining between groups. RESULTS: In group B, the bupivacaine-dye solution stained 16/24 sciatic nerves (67% success). In group US, staining was successfully observed in all 24 nerves (100% success, p < 0.004). The length of nerve staining [median (interquartile range)] was 2 (2-3) mm in group B and 5 (4-6) mm in group US (p < 0.001). One sciatic nerve in group B had injectate distributed over 16 mm, suggestive of an intraneural injection. No signs of laceration or nerve damage were visible under 6× magnification in either group. CONCLUSIONS AND CLINICAL RELEVANCE: The ultrasound-guided approach for sciatic nerve injection demonstrated a higher success rate with superior injectate distribution when compared with the 'blind' approach. Ultrasound guidance is recommended over a 'blind' approach for sciatic nerve block in rats when possible.

Physiological variables for the objective detection of nerve block failure in dogs.

OBJECTIVE: To identify physiological variables for objectively detecting nociception indicative of intraoperative peripheral nerve block failure. STUDY DESIGN: A double-blinded randomized clinical study. ANIMALS: A sample of 14 male (40.8 ± 12 kg; mean ± standard deviation) and 16 female (34.3 ± 11.4 kg) client-owned dogs. METHODS: Dogs were randomly assigned to one of three groups for psoas compartment and proximal sciatic nerve blocks (0.2 mL kg-1 per site): guided bupivacaine (GBB), or saline (GSB) block or a blind bupivacaine block (BBB). Guided blocks were performed using an ultrasound-peripheral nerve locator combination. Premedication consisted of medetomidine 0.01 mg kg-1 and morphine 0.3 mg kg-1. General anaesthesia was induced with propofol and maintained with isoflurane in oxygen. Receiver operator characteristic curve analysis was used to compare actual values and change in values of physiological variables between GSB and GBB. The Youden index and associated criterion for each physiological variable were used to determine an objective measure for nociception. Fisher's exact t test, McNemar's test and Cohen's kappa statistical analysis were used to determine association, differences and inter-score reliability between the objective and subjective scoring for BBB. RESULTS: Cardiovascular variables had good discriminating ability to identify a nociceptive response (p < 0.01). The Youden indices for mean (MAP) and diastolic (DAP) arterial pressure were most reliable in detecting nociception. The highest sensitivity was that of ΔMAP (100%) with good agreement between the subjective and objective scores of Δheart rate or systolic arterial pressure (SAP). The use of ΔMAP, ΔSAP, ΔDAP had the best ability in indicating peripheral nerve block failure (p < 0.001). CONCLUSIONS AND CLINICAL RELEVANCE: Blood pressure values can detect a response to surgical stimulus in adequately anaesthetized dogs. The use of ΔMAP, ΔSAP or ΔDAP may be considered as objective measures to detect nerve block failure.

A randomized clinical trial comparing the efficacy of lidocaine administered intravenously, intranasally or as infraorbital nerve block in dogs undergoing rostral rhinosocopy.

OBJECTIVE: To compare the efficacy of lidocaine administered intravenously, intranasally or as an infraorbital nerve block in dogs undergoing rostral rhinoscopy. STUDY DESIGN: Randomized clinical trial. ANIMALS: A total of 43 client-owned dogs. METHODS: After premedication with medetomidine 0.01 mg kg-1 and methadone 0.2 mg kg-1 intramuscularly, anaesthesia was induced with propofol and maintained with isoflurane in oxygen. Dogs were randomly allocated to receive 2 mg kg-1 of 2% lidocaine as a bilateral infraorbital nerve block (INB) via the caudal intraoral approach, via bilateral topical intranasal administration (TIA) or as an intravenous bolus (IVB). At 5 minutes following lidocaine administration, responses to rhinoscopy (RR) and biopsies (RB) were evaluated using a simple scoring system (0: no reaction; 1: reaction). Response to the rhinoscopy in the recovery period (RE) was recorded. Recovery quality was scored using a simple descriptive score. Heart rate, respiratory rate and noninvasive arterial blood pressure were recorded. Intravenous (IV) fentanyl 0.001 mg kg-1 was administered if an increase > 20% in any variable occurred. Gross movement was attenuated using propofol 0.5 mg kg-1 IV. Scores were analysed using the Chi-square test with Monte Carlo method. Cardiorespiratory changes among and overtime between groups were compared using one-way anova and one-way anova for repeated measures, respectively, or the correspondent non-parametric tests; p < 0.05. RESULT: Of the 43 dogs, 42 completed the study. No statistically significant differences were detected in either physical reactions or changes in cardiorespiratory variables for RR, RB, RE or recovery quality, although RB tended to be higher in group TIA (7/10 versus 1/10 INB and 3/13 IVB).Various cardiorespiratory variables changed overtime within groups. CONCLUSIONS AND CLINICAL RELEVANCE: In dogs, all three investigated techniques attenuated responses during rostral rhinoscopy in dogs, although INB and IVB were more efficacious when biopsies were taken.

Ultrasound-guided sciatic nerve block in Wistar rat cadavers: Relevant anatomy and injection distribution.

OBJECTIVE: To investigate the feasibility of an ultrasound-guided sciatic nerve block by describing the sonoanatomy and comparing the distribution of two volumes of bupivacaine dye solution for nerve staining. STUDY DESIGN: Randomized, experimental, assessor-blinded cadaveric study. ANIMALS: A total of 40 adult female Wistar rat cadavers. METHODS: After studying the sonoanatomy of the sciatic nerve and adjacent structures using a high-resolution linear transducer (19-5 MHz), rat cadavers were randomly divided into two groups that were administered either 0.1 mL (group 0.1) or 0.2 mL (group 0.2) of bupivacaine dye solution per nerve, delivered via an in-plane technique. The extent of nerve staining was subsequently evaluated following dissection. Statistical analysis consisted of assessing data distribution using the Shapiro-Wilk test, followed by paired t-tests for continuous data, Mann-Whitney U test and McNemar's test for categorical data. Statistical significance was defined as p < 0.05. RESULTS: The sciatic nerve was identified bilaterally as a double ellipsoid-shaped image, surrounded by a hyperechoic fascia separating the biceps femoris from the adductor muscle. The hypoechoic structure formed by the bupivacaine dye solution around the nerve was effectively visualized using ultrasound imaging. Sciatic nerve staining was successfully achieved in all pelvic limbs, with dye spread of 4.82 ± 1.55 mm and 5.47 ± 2.18 mm in groups 0.1 and 0.2, respectively (p = 0.128). CONCLUSIONS AND CLINICAL RELEVANCE: This study achieved a detailed understanding of the sonoanatomy of the sciatic nerve and its adjacent structures, highlighting the feasibility of the ultrasound-guided technique for injection in Wistar rats. Furthermore, the results show a comparable distribution of dye solution in both groups. Use of the ultrasound-guided sciatic nerve block technique in rats not only exhibits substantial potential for regional anesthesia but also opens avenues for translational studies.

Ultrasound-guided retromammillary injections in dogs: a feasibility, descriptive and anatomical study.

OBJECTIVE: To evaluate the feasibility of an ultrasound-guided technique targeting the medial branches of the dorsal ramus of the spinal nerves (DRSN) by injecting a dye solution at the caudal aspect of the base of lumbar mammillary processes [i.e. the retromammillary (RM) space]. STUDY DESIGN: Feasibility, descriptive, anatomical study. ANIMALS: Eleven canine cadavers. METHODS: Using anatomical dissections, the relationship between the mammillary processes and the branches of the DRSN of the thoracolumbar and lumbar spine was studied in two cadavers. Subsequently, ultrasound-guided RM injections were administered in nine cadavers, randomly assigned to low volume (LV; 0.01 mL kg-1) of a dye solution at multiple points from L3 to L6 on one side, and high volume (HV; 0.4 mL kg-1) at a single L4 point on the contralateral side. Gross anatomical dissections were immediately performed after the injections. The RM injections were feasible if ultrasonographic landmarks were identifiable in at least 80% of cases, and 80% of LV injections showed medial branch staining. A one-sample binomial test was used for testing feasibility. RESULTS: The medial branches emerged shortly after the DRSN exited the intervertebral foramen and traveled towards the caudal aspect of the base of the mammillary process, which served as the target injection point. With LV, 36 out of 36 (100%) injected medial branches were stained, meeting the criteria of feasibility (p < 0.001). The median (range) number of stained medial branches per cadaver were 4 (4-4) and 2 (1-3), with LV and HV, respectively. Although no lateral branches were stained with LV, 1 (0-2) was stained with HV. Neither ventral branch staining nor epidural spread was noted in any cadaver. CONCLUSIONS AND CLINICAL RELEVANCE: Ultrasound-guided RM injections are feasible and allow for selective staining of the medial branch of the DRSN in canine cadavers at the lumbar spine.

Ultrasound-guided trigeminal nerve approach at the level of the pterygopalatine fossa in cat cadavers.

OBJECTIVE: To describe an ultrasound-guided suprazygomatic approach to the trigeminal nerve block in cat cadavers. STUDY DESIGN: Prospective descriptive study. ANIMALS: Ten feline cadaver heads. METHODS: A 25:75 methylene blue-iopamidol mixture (0.1 mL cm-1 cranium length) was injected into 10 cadaver heads using an ultrasound-guided suprazygomatic approach. A computed tomography (CT) scan was performed to identify contrast presence at the orbital fissure, foramen rotundum and ovale, followed by anatomical dissection to identify staining of the pterygopalatine fossa (PPF), extraconal retrobulbar area, mandibular and maxillary nerves. Descriptive statistics were used to summarize results. RESULTS: A total of 20 injections were performed. Of these, 1/20 misinjection occurred and excluded from further reporting. The volume of injectate was 0.9 (0.9-1.1) mL [median (range)]. Staining of the PPF, extraconal space, maxillary and mandibular nerves over more than 6 mm was achieved in 19/19 (100%), 18/19 (95%), 17/19 (89%) and 19/19 (100%) of injections, respectively. CT showed presence of contrast within 5 mm of the orbital fissure, foramen rotundum and ovale in 18/19 (95%), 19/19 (100%) and 19/19 (100%) of the injections, respectively. No intracranial migration was observed. CONCLUSIONS AND CLINICAL RELEVANCE: This cadaver study illustrates that the suprazygomatic ultrasound-guided trigeminal nerve injection technique can successfully stain the PPF, retrobulbar cone extraconally, mandibular and maxillary nerves. Consequently, this technique has the potential to be used in vivo in cats to desensitize areas innervated by the trigeminal nerve.

Ultrasound-guided sciatic nerve block injections in barred owl (Strix varia) cadavers.

OBJECTIVE: To describe an ultrasound-guided approach to the sciatic nerve and the distribution of nerve staining using two injectate volumes of dye in barred owls. STUDY DESIGN: Descriptive, randomized, assessor-blinded, cadaveric study. ANIMALS: Twelve barred owl cadavers. METHODS: The sciatic nerve was visualized with a 13-6 MHz linear ultrasound probe placed on the medial aspect of the proximal femur in barred owl cadavers. A needle was inserted at the proximal caudal thigh, and cranially advanced in-plane until the tip was immediately adjacent and ventral to the sciatic nerve. Eleven owls were injected bilaterally with a 1:1 solution of 1% methylene blue and 0.5% ropivacaine, with high-volume (HV; 0.4 mL kg-1) and low-volume (LV; 0.2 mL kg-1) treatments. Nerve staining ≥ 1 cm circumferentially was determined by dissection 15 minutes post-injection. The coelom was then opened to inspect for aberrant dye spread. In one barred owl cadaver, a 1:1 solution of 1% methylene blue and 74% ioversol contrast was injected, and computed tomography was performed immediately before and 15 minutes after injection for evaluation of injectate spread. RESULTS: The HV treatment (0.4 mL kg-1) resulted in successful nerve staining in 100% of injections, whereas the LV treatment (0.2 mL kg-1) resulted in successful nerve staining in 91% of injections. There was no leakage of injectate into undesired locations (e.g. coelomic cavity) in any cadaver. CONCLUSIONS AND CLINICAL RELEVANCE: In barred owls, the sciatic nerve can be visualized with ultrasound and injecting a ropivacaine/dye solution under ultrasound guidance successfully stained the sciatic nerve in the majority of cases. This technique holds potential for providing analgesia distal to the stifle joint; however, further investigations are necessary to evaluate its practical application in a clinical setting.

Erector spinae plane block in dogs undergoing hemilaminectomy: A prospective randomized clinical trial.

OBJECTIVE: To compare the perioperative cumulative opioid consumption and the incidence of cardiovascular complications in dogs undergoing hemilaminectomy in which either an erector spinae plane (ESP) block or systemic opioids were administered. STUDY DESIGN: Prospective randomized clinical trial. ANIMALS: A total of 60 client-owned dogs. METHODS: Dogs were randomized to one of three groups: an ESP block (group ESP), a constant rate infusion of fentanyl (group FNT, positive control) or a single dose of methadone as premedication (group MTD, negative control). Intraoperative nociceptive response was treated with fentanyl [1 µg kg-1, intravenously (IV)] boli. Before closure of the surgical site, morphine (0.1 mg kg-1) was applied to the dura mater. The cumulative dose of opioids was recorded and compared between groups. The incidence of intraoperative bradycardia and/or hypotension and the time to extubation were compared between groups. The short form of the Glasgow Composite Pain Scale (SF-GCPS) was used to score nociception before anaesthetic induction and 1, 2, 6, 12,18 and 24 hours postoperatively. Methadone 0.2 mg kg-1 was administered IV if the SF-GCPS score was ≥ 5. RESULTS: Group MTD required more intraoperative rescue analgesia than groups ESP (p = 0.008) and FNT (p = 0.001). The total cumulative intraoperative dose of fentanyl was higher in groups FNT (p < 0.0001) and MTD (p = 0.002) than in group ESP. The incidence of cardiovascular complications was similar between groups. Extubation time was longer in group MTD (p = 0.03). Postoperatively, the time to first rescue analgesia was longer in group ESP than in group MTD (p = 0.03). The cumulative postoperative opioid consumption and pain scores were similar between groups. CONCLUSIONS AND CLINICAL RELEVANCE: The ESP block resulted in a reduced intraoperative opioid consumption compared with the control positive and negative groups.

Evaluation of preoperative rectus sheath block with bupivacaine for analgesia in cats undergoing ovariohysterectomy: a cadaveric and randomized clinical study.

OBJECTIVE: Phase 1: to determine the feasibility of desensitizing ventral branches of spinal nerves within the rectus sheath using an ultrasound-guided rectus sheath block (USRSB). Phase 2: to determine the effect of preoperative USRSB on intraoperative responses to surgical stimulation and postoperative pain. STUDY DESIGN: Cadaveric study and prospective, randomized, blinded, parallel-arm clinical trial. ANIMALS: A group of five cat cadavers and 37 shelter-owned cats undergoing ovariohysterectomy. METHODS: Phase 1: anatomical dissection was performed on one uninjected cadaver. Abdominal walls were dissected in four cadavers (eight hemiabdomens) following bilateral USRSB using 1:1 new methylene blue and 0.5% bupivacaine (0.8 mL kg-1 total). Phase 2: preoperative bilateral USRSB was performed with 0.8 mL kg-1 of 0.25% bupivacaine (RSB) or equivalent volume of 0.9% saline (CONTROL). Intraoperative systolic arterial blood pressure (SAP), heart rate (HR), respiratory rate (fR) and vaporizer setting (vap%) were recorded before skin incision, during celiotomy and abdominal wall closure. In recovery, cats were administered robenacoxib (2 mg kg-1; CONTROL) or 0.9% saline (0.1 mL kg-1; RSB) subcutaneously. Postoperative pain was evaluated for 6 hours using the Glasgow Composite Measure Pain Scale. RESULTS: Phase 1: spinal nerves T9-L3 were identified within the rectus sheath, and stained in 0%, 40%, 63%, 75%, 100%, 88%, 50% and 13% of hemiabdomens, respectively. Phase 2: 37 cats were included (RSB, n = 17; CONTROL, n = 20). Intraoperatively, SAP, HR and fR were not significantly different between groups. Vap% was significantly lower in RSB during celiotomy (p = 0.036) and closure (p = 0.044). Postoperatively, RSB cats were 5.3 times (95% CI 1.8-8.3) more likely to require rescue analgesia than CONTROL cats. CONCLUSIONS AND CLINICAL RELEVANCE: During surgery, USRSB with bupivacaine offered minor benefits and provided markedly less postoperative analgesia than robenacoxib, indicating that relying on USRSB provides insufficient postoperative analgesia for ovariohysterectomy in cats.

Retrospective comparison between low-volume high-concentration and high-volume low-concentration levobupivacaine for bilateral erector spinae plane block in dogs undergoing hemilaminectomy.

OBJECTIVE: To compare the analgesic effect of a bilateral ultrasound-guided erector spinae plane block (ESPB) in dogs undergoing hemilaminectomy using either a low-volume high-concentration (LV-HC) or a high-volume low-concentration (HV-LC) local anaesthetic solution. STUDY DESIGN: Retrospective observational equivalence trial. ANIMALS: A total of 391 client-owned dogs undergoing hemilaminectomy. METHODS: Dogs were assigned to group LV-HC or HV-LC depending on whether 0.2-0.25% levobupivacaine (0.4-0.5 mL kg-1) or 0.125-0.15% levobupivacaine (0.8-1 mL kg-1) was used to perform the ESPB, respectively. The number of dogs in which intraoperative rescue fentanyl boluses were administered, the total dose of fentanyl administered, the overall methadone consumption during the first 24 hours postoperatively and anaesthetic complications were recorded. Univariate and multivariate statistical analyses were performed considering p < 0.05 significant. RESULTS: A total of 248 and 143 dogs were assigned to groups LV-HC and HV-LC, respectively. In group HV-LC, the number of dogs requiring fentanyl intraoperatively (64.3%) was higher (p = 0.0001) than that in group LV-HC (43.5%). The overall intraoperative fentanyl consumption was higher in group HV-LC between the first skin incision and the end of the lamina drilling (p = 0.028). According to the regression analysis, the group allocation was the best variable to predict the intraoperative fentanyl consumption (p < 0.001). Antimuscarinic drugs were administered more frequently in group LV-HC (p < 0.02). However, the prevalence of hypotension and other pharmacological cardiovascular interventions did not differ between groups. No differences in methadone consumption during the first 24 hours postoperatively were found between the groups. CONCLUSIONSAND CLINICAL RELEVANCE: When performing a bilateral ESPB in dogs undergoing hemilaminectomy, compared with HV-LC, the use of LV-HC local anaesthetic solution reduces the intraoperative fentanyl consumption without affecting the postoperative methadone requirement.

Perioperative analgesic efficacy of lumbar erector spinae plane block in dogs undergoing hemilaminectomy: a randomized blinded clinical trial.

OBJECTIVE: To evaluate the perioperative analgesic effect of the unilateral lumbar erector spinae plane block (ESPBL) in dogs undergoing hemilaminectomy. STUDY DESIGN: Randomized, blinded clinical study. ANIMALS: A total of 30 client-owned dogs undergoing thoracolumbar or lumbar hemilaminectomy for intervertebral disc extrusion (IVDE). METHODS: Dogs were randomly assigned to receive a unilateral ESPBL, performed either with 0.4 mL kg-1 ropivacaine 0.5% [group ROPI (n = 15)] or with saline solution [CNT group (n = 15)]. Dogs were premedicated intravenously (IV) with acepromazine 5 µg kg-1 and methadone 0.2 mg kg-1, general anaesthesia was induced by administering IV midazolam 0.2 mg kg-1 and propofol to effect and maintained with isoflurane. Fentanyl was administered as rescue analgesia. Bradycardia [heart rate (HR) < 60 beats minute-1] with hypotension was treated with atropine IV. The Short-Form of the Glasgow Composite Pain Scale was used pre- and postoperatively at 1, 2, 4, 8, 12, 16, 20 and 24 hours after extubation, and methadone 0.2 mg kg-1 was administered IV when pain score was ≥ 5/20. HR and end-tidal concentration of isoflurane (Fe'Iso) were compared between groups with anova combined with a Dunnet's post hoc test. Time to the first rescue methadone and total dose of fentanyl (FENtot, µg kg-1 hour-1) and methadone (METtot, mg kg-1) in the first 24 postoperative hours were compared using unpaired Student's t test. Postoperative pain scores were compared with the Mann-Whitney test and atropine administration with a Fisher's exact test; p < 0.05. RESULTS: HR, Fe'Iso, FENtot, METtot and atropine administration were significantly lower in group ROPI compared to CNT. Postoperative analgesic effect was significantly longer, and pain scores were significantly lower in group ROPI for all time points. CONCLUSIONS AND CLINICAL RELEVANCE: Unilateral ESPBL with ropivacaine reduced perioperative opioid consumption and the occurrence of bradycardia in dogs undergoing hemilaminectomy.

Greater ischiatic notch plane versus parasacral block in dogs undergoing pelvic limb surgery: a retrospective noninferiority cohort study on perioperative opioid consumption.

OBJECTIVE: To compare perioperative opioid consumption in dogs undergoing pelvic limb surgeries and receiving a lumbosacral plexus block by combining a lumbar [lateral pre-iliac (LPI)] block with a lumbosacral trunk [i.e. parasacral (PS group) or greater ischiatic notch plane (GIN group)] block. Study design Retrospective, descriptive, exploratory, noninferiority cohort study. METHODS: Medical records of 37 client-owned dogs were analyzed. Intraoperative (primary outcome) and postoperative (24 hours) opioid use, 24 hour cumulative pain scores and prevalence of complications were compared between the two groups. Opioid use was quantified in morphine equivalents (ME, mg kg-1 ). The noninferiority limit for intraoperative opioid consumption was set at 0.05 ME kg-1 hour-1. Demographic data, procedure duration, surgery type and perioperative dexmedetomidine and ketamine use were also collected. A t-test or Wilcoxon rank-sum test, a Fisher's exact test and multivariable linear regression were used. Significance was set at p < 0.05. RESULTS: The GIN and PS groups comprised 17 and 20 dogs, respectively. Total intraoperative ME consumption was 0.17 (0.11-0.21) and 0.22 (0.16-0.30) mg kg-1 hour-1 for the GIN and PS groups, respectively (p = 0.077). The noninferiority analysis adjusted by surgery type and body mass revealed that the mean difference between the groups (GIN - PS) was -0.039 (95% CI -0.11-0.03, p = 0.247) ME mg kg-1 hour-1, indicating that the GIN group was not inferior to the PS group regarding intraoperative ME consumption. Dexmedetomidine and ketamine use, postoperative ME consumption and pain scores were similar between groups. CONCLUSIONS AND CLINICAL RELEVANCE: This retrospective study and preliminary observations support the clinical use of the GIN plane block, demonstrating its noninferiority to the PS block when combined with the LPI block for multimodal perioperative analgesia in dogs undergoing pelvic limb surgeries.

Comparative study between lateral versus latero-ventral quadratus lumborum block for perioperative analgesia in canine laparoscopic ovariectomy.

OBJECTIVE: To compare the perioperative analgesic effect of lateral versus latero-ventral quadratus lumborum block (QLB) in dogs undergoing laparoscopic ovariectomy. STUDY DESIGN: Randomized, blinded clinical study. ANIMALS: A total of 15 client-owned female dogs undergoing laparoscopic ovariectomy. METHODS: Animals were randomly assigned to receive a bilateral QLB, performed with 0.3 mL kg-1 ropivacaine 0.5%, either with lateral (group LQLB, n = 7) or latero-ventral approach (group LVQLB, n = 7). Dogs were premedicated intramuscularly with methadone 0.2 mg kg-1 and dexmedetomidine 3 µg kg-1. General anaesthesia was induced intravenously (IV) with propofol and maintained with isoflurane. Cardiovascular and respiratory variables were continuously monitored and recorded every 5 minutes during surgery. Fentanyl 3 µg kg-1 was administered IV if there was a 20% increase in heart rate and/or mean arterial pressure from previous values recorded 5 minutes before. Meloxicam 0.2 mg kg-1 was administered IV to all dogs during recovery. The short-form of the Glasgow Composite Pain Scale was used hourly for 8 hours post-QLB. Methadone 0.2 mg kg-1 was administered IV when pain score was ≥ 6/24. A chi-square test compared the number of dogs requiring intraoperative rescue fentanyl. A Friedman test with a Dunn's post hoc was used to evaluate the trend in postoperative pain scores within each group, and a Mann-Whitney U test compared scores between the groups at each time point; p < 0.05. RESULTS: Significantly fewer dogs required intraoperative rescue fentanyl in group LQLB than in group LVQLB. No dog required postoperative rescue methadone, and there were no significant differences in pain scores. CONCLUSIONS AND CLINICAL RELEVANCE: Bilateral QLB performed with lateral approach reduced the number of dogs requiring intraoperative rescue analgesia in comparison with the latero-ventral approach. No differences were detected postoperatively, possibly owing to the confounding effects of methadone, dexmedetomidine and meloxicam.

A comparison of the motor effects and analgesic efficacy following lumbar plexus block combined with sciatic nerve block or epidural in dogs undergoing tibial plateau leveling osteotomy.

OBJECTIVE: To compare motor effects and analgesic efficacy following an ultrasound-guided lateral approach to lumbar plexus blockade at L7 and sciatic nerve blockade (LPSNB) against epidural injection in dogs undergoing tibial plateau leveling osteotomy (TPLO). STUDY DESIGN: Prospective, randomized, blinded clinical trial. ANIMALS: A total of 27 healthy adult dogs undergoing unilateral TPLO surgery. METHODS: Dogs were allocated to either LPSNB (bupivacaine 2 mg kg-1, 0.75%) or epidural (morphine PF 0.1 mg kg-1 and bupivacaine 0.5 mg kg-1, 0.75%). Other aspects of clinical management were identical, including anesthetic drug protocol, area of presurgical clipping and bladder care. Time to perform the block, response to surgical stimuli, pain scores, rescue analgesia, time to stand and walk, motor score and time to first urination were recorded. One evaluator, unaware of treatment status, performed all evaluations. Student's t-test or Mann-Whitney U test was used to compare continuous variables between groups, and Fisher's exact test for categorical variables. RESULTS: Median (range) times to stand and walk were shorter for LPSNB [60 (40-120) minutes and 90 (60-150) minutes, respectively, p = 0.003] than for epidural [150 (120-240) minutes and 180 (120-360) minutes, respectively, p = 0.006]. Four dogs required rescue intraoperatively (three in epidural group, one in LPSNB group, p = 0.438). Pain scores over the 24 hour evaluation period were similar, and not significantly different, for each group. Time to spontaneous urination [LPSNB, 330 (240-360) minutes; epidural, 300 (120-1440) minutes, p = 1.0] did not differ between groups. CONCLUSIONS AND CLINICAL RELEVANCE: An ultrasound-guided lateral paravertebral approach to the lumbar plexus within the psoas compartment at L7, combined with sciatic nerve blockade, allows faster return to normal motor function, with similar pain control and impact on urination when compared with epidural in dogs after TPLO surgery.