Computed tomographic laryngotracheal dimensions in adult domestic rabbits (Oryctolagus cuniculus) are positively associated with body weight and the laryngotracheal lumen is narrowest at the level of the thyroid cartilage.

OBJECTIVE: This retrospective study aimed to measure rabbit laryngotracheal dimensions at different locations on computed tomography (CT), assess the relationship of these measurements with rabbit body weight, determine the most common narrowest measurement and assess its relationship with endotracheal tube (ETT) size and body weight. ANIMALS: 66 adult domestic rabbits (Oryctolagus cuniculus) of different breeds and body weights. PROCEDURES: CT laryngotracheal luminal height, width, and cross-sectional area measurements were made at the rostral thyroid cartilage at the level of the arytenoids, caudal thyroid cartilage/rostral cricoid cartilage, caudal cricoid cartilage/cranial trachea, and trachea at the level of the fifth cervical vertebra. RESULTS: The data for every measurement of luminal airway dimensions revealed robust positive associations with body weight (P < .001). The narrowest laryngotracheal measurement was the width at the level of the caudal thyroid cartilage/rostral cricoid cartilage, and the smallest cross-sectional area was at the rostral thyroid cartilage at the level of the arytenoids. There was a strong association between body weight and the likelihood of appropriate ETT fit. To have at least an 80% chance of appropriate ETT fit with a 2.0, 2.5, and 3.0 mm ETT, the rabbits' weight predicted by the model (lower 95% confidence limit) were at least 2.99 (2.72) kg, 5.24 (4.65) kg, and 5.80 (5.21) kg, respectively. CLINICAL RELEVANCE: The laryngotracheal lumen was narrowest at the level of the caudal thyroid cartilage in rabbits, which indicates this location may be the limiting factor in determining ETT size in rabbits.

Evaluation of ultrasound-guided pecto-intercostal block in canine cadavers.

OBJECTIVE: To describe the technique for performing an ultrasound-guided pecto-intercostal fascial (PIF) block and compare two volumes of injectate in canine cadavers. STUDY DESIGN: Prospective experimental cadaveric study. ANIMALS: A total of 11 canine cadavers (11.8 ± 1.9 kg). METHODS: Parasternal ultrasound-guided injections were performed within the PIF plane, between the deep pectoral and external intercostal muscles, at the intercostal space between ribs four and five. Each hemithorax was injected with 0.25 mL kg-1 (treatment low volume, LV) or 0.5 mL kg-1 (treatment high volume, HV) of 1% methylene blue dye. Treatments were randomly assigned to either right or left hemithorax, with each cadaver injected with both treatments, for a total of 22 injections. Anatomical dissections were performed to determine staining of ventral cutaneous branches of intercostal nerves, surrounding nerves and musculature and spread of injectate. The presence or absence of intrathoracic puncture was also noted. RESULTS: The PIF plane was identified and injected in each hemithorax. No significant differences between treatments LV and HV were found for number of ventral cutaneous nerve branches stained or any other analyzed variable. The ventral cutaneous branches of intercostal nerves (T3-T8) were variably stained, and the most commonly stained nerves were T5 (6 and 10), T6 (8 and 9) and T7 (2 and 7) in treatments LV and HV, respectively. Staining outside the immediate parasternal region was noted in both treatments, with greater spread away from the parasternal region in treatment HV. No intrathoracic staining was found. CONCLUSIONS AND CLINICAL RELEVANCE: Ultrasound-guided PIF injections resulted in staining of ventral cutaneous branches and parasternal musculature; however, the spread observed was inadequate to provide effective analgesia to the sternum. In vivo studies are warranted to investigate this regional anesthetic technique in veterinary patients.

Description of an ultrasound-guided rectus sheath block injection technique and the spread of dye in calf cadavers.

OBJECTIVES: To describe an ultrasound-guided rectus sheath (RS) block technique in calves with injections of methylene blue and assess the extent of injectate spread and nerve staining in calf cadavers. STUDY DESIGN: Prospective, experimental, blinded cadaveric study. ANIMALS: A total of 16 calf cadavers weighing 30.7 ± 7.1 kg. METHODS: Using an ultrasound-guided, in-plane technique, each cadaver was injected with both a low (LV; 0.25 mL kg-1) and high (HV; 0.5 mL kg-1) volume of methylene blue dye. Volumes were randomly assigned to the left or right hemiabdomen. Ultrasound imaging was scored based on landmarks and needle visualization, and duration to perform injections were assessed. Dissections were performed immediately after injections. Staining of ventral branches of spinal nerves and the extent of dye spread were recorded by an anatomist unaware of treatment allocation. RESULTS: The number of nerves stained in treatments LV and HV were 2.3 ± 1.7 and 4.4 ± 1.3, respectively (p = 0.0001). Branches of thoracic nerves T7-13 and lumbar nerves L1-2 were completely stained 6.3%, 6.3%, 31.3%, 62.5%, 56.3%, 37.5%, 31.3%, 6.3% and 0%, respectively, in treatment LV and 0%, 12.5%, 50%, 93.8%, 100%, 93.8%, 62.5%, 25% and 6.3%, respectively, in treatment HV. Ultrasound imaging was scored excellent in most cadavers and needle visualization deemed excellent in all injections. The mean duration to perform RS injections in both treatments was 2 (range, 1-6) minutes. CONCLUSIONS AND CLINICAL RELEVANCE: Nerve staining results from treatment HV suggest that this RS injection technique could be clinically useful in ventral midline surgical procedures, including umbilical procedures, in calves. This study supports future clinical trials in calves.

Sedation and Anesthesia of Lizards.

The field of lizard sedation, anesthesia, and locoregional anesthesia is advancing with new drug protocols being evaluated, and new locoregional techniques being developed and evaluated. Inducing and maintaining effective and safe chemical restraint in lizards can be challenging, particularly in systemically diseased individuals. Understanding the anatomic and physiologic adaptations of lizards, using reversible or partially reversible injectable protocols, and using locoregional anesthesia may increase the quality of chemical restraint, facilitate faster recoveries, and limit anesthesia-related morbidity and mortality.

Neuraxial administration of morphine combined with lidocaine induces regional antinociception in inland bearded dragons (Pogona vitticeps).

OBJECTIVE: To assess the antinociceptive efficacy and safety of neuraxial morphine in inland bearded dragons (Pogona vitticeps). ANIMALS: 10 healthy adult bearded dragons. PROCEDURES: Animals were sedated with alfaxalone (15 mg/kg) SC prior to neuraxial injections. In a randomized, blinded, placebo-controlled, crossover design, animals received preservative-free morphine (0.5 mg/kg) combined with lidocaine (2 mg/kg) or lidocaine (2 mg/kg) only (control treatment). For both treatments, saline (0.9% NaCl) solution was used for dilution to a total volume of 0.3 mL/kg. If the initial injection did not result in motor block of the pelvic limbs or cloaca relaxation within 10 minutes, a second injection was performed. Measurements consisted of bilateral mechanical stimulation of the limbs and at 25%, 50%, and 75% of the trunk's length as well as cloacal tone to assess spread and duration of motor block. Pelvic limb withdrawal latencies in response to a thermal noxious stimulus were measured over a 48-hour period to assess antinociception. RESULTS: Success rate following the first injection was 90% (18/20 injections) and increased to 100% following a second injection. Motor block occurred within 5 minutes with both treatments. Pelvic limb withdrawal latencies were significantly prolonged following neuraxial morphine versus control treatment for at least 12 hours after injection. By 24 hours, no effect of morphine on pelvic limb latencies was detectable. CLINICAL RELEVANCE: These results demonstrated that neuraxial administration of morphine results in regional antinociceptive effects for at least 12 hours and has no clinically relevant adverse effects in healthy bearded dragons. This technique has potential for providing regional analgesia in this species.

Impact of endotracheal tube size and cuff pressure on tracheal and laryngeal mucosa of adult horses.

OBJECTIVE: To assess the effects of two sizes of silicone endotracheal tubes with internal diameter 26 mm (ETT26) and 30 mm (ETT30) inflated to minimum occlusive volume on tracheal and laryngeal mucosa of adult horses anesthetized for 2 hours with isoflurane. STUDY DESIGN: Prospective, randomized, blinded, crossover experimental study. ANIMALS: A total of eight healthy adult mares. METHODS: Upper airway endoscopy and ultrasound measurements of internal tracheal diameter were performed the day before anesthesia. Horses were anesthetized and orotracheally intubated with ETT26 or ETT30. Ease of intubation was scored. The cuff was inflated in 10 mL increments to produce a seal. Final volume of air used and intracuff (IC) pressure (measured by pressure transducer) were recorded. At the end of anesthesia, a manometer was used to measure IC pressure and these measurements compared against measurements from the pressure transducer. Laryngeal and tracheal mucosa were assessed via endoscopy and assigned a score 0-3 before anesthesia, and at 2 and 24 hours following extubation. RESULTS: Data are from seven horses because one horse with laryngeal hemiplegia was excluded. Mean tracheal ultrasound measurement was 3.5 ± 0.4 cm. No significant differences were noted between endotracheal tube sizes for intubation score, IC pressures, inflation volumes or tracheal or laryngeal injury scores at any time point. IC pressure measured by manometer was slightly higher than that by transducer (+1.0 ± 2.8 mmHg). CONCLUSIONS AND CLINICAL RELEVANCE: Results identified no clear advantage of one endotracheal tube size over the other in the population of horses studied, when endotracheal intubation is properly applied and IC pressure is carefully monitored. However, given that ETT26 was associated with the highest observed IC pressures and the only observed incidents of tracheal circumferential erythema, the larger ETT30 may be the better choice in most cases where tracheal size is sufficient.

Evaluation of neuraxial administration of bupivacaine in bearded dragons (Pogona vitticeps).

OBJECTIVE: To assess the success rate, onset, duration and extent of motor/sensory block following neuraxial injection of two dosages of bupivacaine in bearded dragons (Pogona vitticeps). STUDY DESIGN: Prospective, randomized, blinded, crossover experimental study. ANIMALS: A total of 10 adult bearded dragons (0.3 ± 0.1 kg). METHODS: After sedation with alfaxalone (15 mg kg-1 subcutaneously), neuraxial injections were performed with 1 or 2 mg kg-1 bupivacaine hydrochloride (0.5%, treatments BUP-1 and BUP-2, respectively) in a randomized treatment sequence with a 7 day washout period. If the initial bupivacaine injection was not successful within 10 minutes, a second injection was performed at the same dose. Mechanical stimulation of limbs, 25%, 50%, 75% of the trunk's length and cloacal tone were assessed. RESULTS: Success rate following the first neuraxial injection was 95%, which increased to 100% after the second injection. Motor/sensory block were noted by 5 minutes after the injection of bupivacaine at either dose. BUP-2 was associated with more cranial spread. The median (range) duration of cloacal tone loss was longer following treatment BUP-2 [120 (75-225) minutes] than followed treatment BUP-1 [83 (25-135) minutes; p = 0.03]. Duration of pelvic limb motor block was comparable between both doses, lasting a median of 68 minutes in both treatments (p = 0.94). There was a transient, not clinically relevant increase from baseline in heart rate in treatment BUP-1 only. No significant difference from baseline in respiratory rate was noted in either treatment; however, two animals in treatment BUP-2 became apneic (10-20 minutes). CONCLUSIONS AND CLINICAL RELEVANCE: Bupivacaine (1 mg kg-1) is recommended for neuraxial anesthesia in bearded dragons. In treatment BUP-2, extensive cranial spread resulted in apnea and motor block of the thoracic limb in several animals; therefore this dose is not recommended.

Evaluation of supraglottic airway device use during inhalation anesthesia in healthy African pygmy hedgehogs (Atelerix albiventris).

OBJECTIVE: To evaluate a supraglottic airway device (SGAD) designed for rabbits in African pygmy hedgehogs (Atelerix albiventris) during inhalation anesthesia. STUDY DESIGN: Prospective, randomized, blinded experimental study. ANIMALS: A total of 12 adult African pygmy hedgehogs (seven male, five female). METHODS: Hedgehogs were placed in a chamber and anesthesia was induced using isoflurane in oxygen. Oropharyngeal endoscopy was performed and video recorded. The SGAD (v-gel R1) was inserted and connected to a Mapleson D circuit. Capnography, pulse oximetry and physiologic variables were measured during anesthesia, and lung inflation was tested at 10 and 20 cmH2O. With the SGAD temporarily disconnected, anesthetized hedgehogs were randomly positioned into right and left lateral, dorsal and sternal recumbency to evaluate the effect of a change in body position on SGAD placement. Oropharyngeal endoscopy was repeated at the end of anesthesia, and recovery time was recorded. Pre- and post-SGAD placement endoscopy videos were retrospectively reviewed and scored for gross trauma. RESULTS: The median [interquartile range (IQR)] time to successful SGAD placement was 38 (16-68) seconds. The time to SGAD placement decreased as the study progressed. SGAD required repositioning in six hedgehogs, median 2.5 (IQR, 1-3.5) adjustments each, to successfully perform lung inflation or maintain capnography readings. Lung inflation at 10 cmH2O was successfully performed without leakage in nine animals, and in the other three animals after adjusting the SGAD at 1-2 time points. Inflation at 20 cmH2O was rarely achieved without an air leak. Changes in heart and respiratory rates during anesthesia were not clinically relevant. Median endoscopic scores were 0 (no lesions) for both pre-and postplacement. CONCLUSIONS AND CLINICAL RELEVANCE: The SGAD was relatively quickly and easily placed, permitted lung inflation and caused no significant oropharyngeal damage. The SGAD is a practical option for airway management in African pygmy hedgehogs.

Efficacy of greater auricular and auriculotemporal nerve blocks performed in rabbits.

OBJECTIVE: To evaluate the efficacy, duration and safety of greater auricular and auriculotemporal nerve blocks in rabbits. STUDY DESIGN: Prospective, randomized, crossover, experimental study. ANIMALS: A total of 11 healthy adult Dutch-belted rabbits. METHODS: The rabbits underwent general anesthesia and injections of the greater auricular and auriculotemporal nerves using either bupivacaine (0.3 mL kg-1, 0.5%) or the same volume of saline. After anesthesia, the efficacy and duration of nerve blocks were assessed using analgesiometry forceps on the pinna and cotton-tipped applicators within the vertical ear canal. Rabbits were monitored for abnormal carriage of the ear and auriculopalpebral nerve block of the ipsilateral eye. Body weight, food intake, fecal output and fecal pellet diameter were measured daily for 6 days after the nerve blocks were performed and compared with baseline to assess short-term effects. RESULTS: The greater auricular nerve was successfully blocked in 12/16 (75%) ears for mean ± standard deviation duration of 88 ± 52 minutes. In successfully blocked ears, altered ear position was noted in five/16 (31%) cases. The auriculotemporal nerve was blocked in one/16 ears for 120 minutes. The auriculopalpebral nerve was inadvertently blocked in three/16 ears. Food intake and fecal output decreased significantly during the treatment day but returned to pretreatment values after 24 hours. There was no change in body weight or fecal pellet diameter for either treatment. CONCLUSIONS AND CLINICAL RELEVANCE: The results suggest that duration of the greater auricular nerve block with 0.5% bupivacaine was short-lived in the live rabbit. Auriculotemporal nerve block was only achieved in one ear; therefore, further studies are warranted to evaluate the contribution of these blocks in the pain management of rabbits undergoing auricular surgery.

Effect of contrast and local anesthetic on dye spread following transversus abdominis plane injection in dog cadavers.

OBJECTIVE: To determine whether the addition of bupivacaine or contrast medium to methylene blue dye would affect dye distribution following ultrasound (US)-guided transversus abdominis plane (TAP) injections. STUDY DESIGN: Prospective, randomized, blinded cadaveric study. ANIMALS: A total of 29 fresh Beagle dog cadavers. METHODS: Each hemiabdomen (n = 58) was randomized into one of three groups: group M, 1% methylene blue; group MB, 50:50 mixture of 1% methylene blue and 0.5% bupivacaine; group MC, 25:75 mixture of 1% methylene blue and contrast agent (iohexol). TAP injections (0.5 mL kg-1) were performed bilaterally by a trained individual followed by dissection of the abdominal walls. Craniocaudal and dorsoventral spread along tissue planes was measured. Staining of branches of the thoracic and lumbar spinal nerves was considered successful when dye on the nerve was >10 mm. One-way anova with post hoc Tukey test was used to compare craniocaudal and dorsoventral spread and Kruskal-Wallis test to compare incidence of nerve staining among groups. RESULTS: TAP injections were successful in 52 out of 58 hemiabdomens. Dorsoventral spread was greater for group M (60 ± 10 mm) compared with MC (49 ± 9 mm; p = 0.01) but not MB (52 ± 9 mm; p = 0.09). No difference was found in craniocaudal spread or number of nerves stained among groups. CONCLUSION AND CLINICAL RELEVANCE: The significant difference found in spread of tissue staining between methylene blue alone and methylene blue mixed with contrast in the TAP blocks should be kept in mind when interpreting dye-based cadaveric regional anesthesia studies.

Ultrasound-guided rectus sheath block: an anatomic study in dog cadavers.

OBJECTIVES: To describe the ultrasound-guided rectus sheath block technique and the anatomical spread of two volumes of methylene blue injection in dog cadavers. STUDY DESIGN: Blinded, prospective, experimental cadaveric study. ANIMALS: A total of eight dog cadavers weighing 8.9 ± 1.6 kg. METHODS: Ultrasound-guided rectus sheath injections were performed bilaterally 1 cm cranial to the umbilicus using 0.25 mL kg-1 (low volume; LV) and 0.50 mL kg-1 (high volume; HV) of 0.5% methylene blue dye. A total of 16 hemiabdomens were injected. The ultrasound image quality of the muscular and fascial plane landmarks and needle visualization were scored using a standardized scale. Cadavers were dissected to determine the distribution of the dye and to assess staining of ventral branches of the spinal nerves. RESULTS: Fewer ventral spinal nerve branches were stained in the LV group than in the HV group, at 2.00 ± 0 and 2.90 ± 0.83, respectively (p < 0.01). Ventral branches of thoracic (T) and lumbar (L) spinal nerves (T10, T11, T12, T13 and L1) were stained 25%, 100%, 75%, 25% and 0% of the time in LV group and 12.5%, 87.5%, 100.0%, 75.0% and 13.0% in HV group. A lesser extent of cranial-caudal dye distribution was observed in the LV group than in the HV group (7.1 ± 1.8 cm and 9.2 ± 1.8 cm, respectively; p = 0.03). There was no significant difference in medial-lateral spread of dye, number of test doses or ultrasound image quality scores between groups. CONCLUSIONS AND CLINICAL RELEVANCE: The results of this study suggest that, on an anatomical basis, this easily performed block has the potential to provide effective abdominal wall analgesia for the ventral midline. This study supports the potential of the rectus sheath block for abdominal procedures, and further investigations on its clinical efficacy are warranted.

Evaluation of the sedative and physiological effects of intramuscular lidocaine in bearded dragons (Pogona vitticeps) sedated with alfaxalone.

OBJECTIVE: To evaluate if intramuscular (IM) lidocaine potentiates the sedative effects of alfaxalone and results in cardiopulmonary changes in sedated bearded dragons. STUDY DESIGN: Prospective experimental crossover study. ANIMALS: A group of eight adult bearded dragons (Pogona vitticeps) weighing 334 ± 46 g. METHODS: Animals were administered alfaxalone (10 mg kg-1 subcutaneously) and 15 minutes later either lidocaine 2% (4 mg kg-1) or 0.9% sodium chloride (0.2 mL kg-1) was administered IM in the thoracic limb. The treatments were randomized and separated by 7 days. Sedation was scored based on body position, eye closure, jaw tone, swallowing, pick up response, righting reflex and pelvic limb withdrawal reflex. Heart rate (HR) and respiratory rate (fR) were recorded every 5 minutes until recovery from sedation. RESULTS: Lidocaine had no significant effect on duration or depth of alfaxalone sedation. HR increased significantly for <10 minutes following lidocaine administration by a median (interquartile range) of 33% (28-37%; p = 0.024). No clinically significant effects on fR occurred following lidocaine injection. CONCLUSIONS AND CLINICAL RELEVANCE: Administration of lidocaine 2% (4 mg kg-1) IM did not potentiate alfaxalone sedation but resulted in a transient clinically relevant increase in HR.

Description of an ultrasound-guided erector spinae plane block and the spread of dye in dog cadavers.

OBJECTIVES: To describe a technique to perform an ultrasound-guided erector spinae plane (ESP) block and determine the distribution and potential complications after injection of two volumes of methylene blue in dog cadavers. STUDY DESIGN: Prospective experimental cadaveric study. ANIMALS: A total of eight dog cadavers weighing 9.3 ± 1.9 kg. METHODS: Ultrasound-guided injections dorsal to the transverse process and ventral to the erector spinae muscles aimed at the fifth thoracic transverse process were performed bilaterally in each dog using 0.5 and 1.0 mL kg-1 dye solution [low volume (LV) and high volume (HV) treatments, respectively]. Treatments were randomly assigned to the right or left side of each dog, resulting in a total of 16 injections. Anatomical dissections determined dye spread characteristics, including epaxial muscles spread, staining of spinal nerves, dorsal rami, ventral rami (intercostal nerves) and sympathetic trunk spread. Staining indicating potential complications (epidural, mediastinal and intrapleural spread) was recorded. RESULTS: There was complete staining of at least one dorsal ramus following all injections. A more extensive spread was observed along the muscles in the HV compared with LV (p = 0.036). No significant difference between multisegmental dorsal rami spread (six out of eight injections in each treatment) was noted. Out of 16 injections, one in LV treatment resulted in multisegmental spinal nerve staining and one in HV treatment resulted in ventral ramus (intercostal nerve) staining. Use of anatomic landmarks resulted in inaccurate identification of the fifth transverse process in at least six out of 16 injections (38%). No sympathetic trunk, epidural, mediastinal or intrapleural staining was observed. CONCLUSIONS AND CLINICAL RELEVANCE: Ultrasound-guided ESP injections resulted in extensive staining along the epaxial muscles, as well as staining of the dorsal rami in all dogs. The incidence of dorsal rami mutisegmental spread was the same in both treatments.

Evaluation of neuraxial anesthesia in bearded dragons (Pogona vitticeps).

OBJECTIVE: To assess the feasibility, success rate, onset, duration and extent of motor/sensory block following intrathecal injection of lidocaine in bearded dragons (Pogona vitticeps). STUDY DESIGN: Prospective experimental study. ANIMALS: A group of eight adult bearded dragons (0.333 ± 0.048 kg). METHODS: The animals were sedated with alfaxalone (15 mg kg-1) subcutaneously. Neuraxial injections were performed with 1% lidocaine (2 mg kg-1) or 0.9% sodium chloride (0.2 mL kg-1) in all animals with a 7 day interval. If the initial injection did not result in motor block of the pelvic limbs within 10 minutes, a second injection was performed at the same dose. Measurements consisted of bilateral mechanical stimulation of limbs; 25%, 50%, and 75% of the trunk's length; and cloacal tone. Animals were monitored for any untoward side effects by monitoring heart rate (HR), respiratory rate, righting reflex and head position. RESULTS: Success rate following the first injection of lidocaine was 50% (four out of eight animals) and increased to 75% (six out of eight animals) following a second injection. Onset of motor/sensory block occurred within 5 minutes in all successful injections. Duration and extent were variable, with most bearded dragons presenting motor/sensory block of cloaca and pelvic limbs (six out of six) and 25% of the trunk (five out of six) with mean ± standard deviation (range) duration of 49 ± 28 (25-100), 48 ± 25 (25-90) and 40 ± 14 (25-50) minutes, respectively. Confirmation of intrathecal injection by aspiration of cerebrospinal fluid was not possible. Neuraxial lidocaine significantly increased depth and duration of sedation, with a transient increase in HR, compared with saline. CONCLUSION AND CLINICAL RELEVANCE: Neuraxial lidocaine is a feasible technique with moderate success rate and low risk of complication in bearded dragons. This technique has potential for improving the management of anesthesia in this species.

Description of an ultrasound-guided thoracic paravertebral block technique and the spread of dye in dog cadavers.

OBJECTIVES: To describe an ultrasound-guided thoracic paravertebral block and determine the distribution after injection of two volumes of methylene blue in dog cadavers. STUDY DESIGN: Prospective experimental cadaveric study. ANIMALS: Twelve dog cadavers weighing 11 ± 3 kg. METHODS: Ultrasound-guided injections aimed at the fifth thoracic (T5) paravertebral space were performed in randomized order using 0.1 or 0.3 mL kg-1 dye solution (six dogs for each volume). Anatomic dissections determined dye spread characteristics, including the presence and degree of staining of spinal nerves, and the presence of intercostal and sympathetic trunk spread. Staining of mediastinum, epidural, intrapleural and contralateral thoracic paravertebral space was recorded. RESULTS: There was no significant difference in dye distribution between groups. The use of anatomic landmarks resulted in the inaccurate identification of the T5 paravertebral space. The T4, T5 and T6 paravertebral spaces were injected in four, five and three of 12 dogs, respectively. Complete staining of the spinal nerve of the thoracic paravertebral space injected was observed in 11 of 12 dogs, and partial staining in one dog in the low-volume group. Multisegmental distribution was demonstrated with staining of contiguous spinal nerves in one dog in the high-volume group, and multiple segments of intercostal (three dogs) and sympathetic trunk (four dogs) spread in both groups. No mediastinal, epidural, intrapleural or contralateral thoracic paravertebral space staining was observed. CONCLUSIONS AND CLINICAL RELEVANCE: Ultrasound-guided injection at the thoracic paravertebral space resulted in staining of the spinal nerve in all dogs. However, T5 paravertebral space was not accurately identified using anatomic landmarks. Dye distribution was not significantly different between the two groups; therefore, the use of the lower-volume and multiple-site injections would be potentially necessary in clinical cases to achieve ipsilateral blockade of the thoracic wall.

Effects of ketamine, propofol, or thiopental administration on intraocular pressure and qualities of induction of and recovery from anesthesia in horses.

OBJECTIVE: To assess the effects of ketamine hydrochloride, propofol, or compounded thiopental sodium administration on intraocular pressure (IOP) and qualities of induction of and recovery from anesthesia in horses. ANIMALS: 6 healthy adult horses. PROCEDURES: Horses were sedated with xylazine hydrochloride (0.5 mg/kg), and anesthesia was induced with guaifenesin followed by ketamine (2 mg/kg), propofol (3 mg/kg), or thiopental (4 mg/kg) in a crossover study with ≥ 1 week between treatments. For each horse, IOP in the right eye was measured with a handheld applanation tonometer before and after xylazine administration, at the time of recumbency, and every 3 minutes after induction of anesthesia until spontaneous movement was observed. Cardiorespiratory responses and venous blood measurements were recorded during anesthesia. Induction of and recovery from anesthesia were subjectively evaluated by investigators who were unaware of the anesthetic treatment of each horse. Data were analyzed via a repeated-measures ANOVA with Holm-Sidák post hoc comparisons. RESULTS: Compared with findings after xylazine administration (mean ± SD, 17 ± 3 mm Hg), thiopental decreased IOP by 4 ± 23%, whereas propofol and ketamine increased IOP by 8 ± 11% and 37 ± 16%, respectively. Compared with the effects of ketamine, propofol and thiopental resulted in significantly lower IOP at the time of recumbency and higher heart rates at 3 minutes after induction of anesthesia. No other significant differences among treatments were found. CONCLUSIONS AND CLINICAL RELEVANCE: These findings support the use of thiopental or propofol in preference to ketamine for horses in which increases in IOP should be minimized.

Effect of epidural and intravenous use of the neurokinin-1 (NK-1) receptor antagonist maropitant on the sevoflurane minimum alveolar concentration (MAC) in dogs.

OBJECTIVE: To determine the effect of maropitant, an NK-1 receptor antagonist on the minimum alveolar concentration (MAC) of sevoflurane after intravenous and epidural administration to dogs. STUDY DESIGN: Prospective experimental study. ANIMALS: Seven, adult, spayed-female dogs (24.8 ± 1.9 kg). METHODS: Each dog was anesthetized twice with sevoflurane in oxygen, with at least 10 days separating the anesthetic events. The minimum alveolar concentration (MAC) of sevoflurane was determined using the tail-clamp technique. During the first anesthetic event, the MAC of sevoflurane was determined initially and again after intravenous administration of maropitant (5 mg kg(-1)) and an infusion (150 µg kg(-1) hour(-1)). During the second anesthetic event, an epidural catheter was advanced to the 4th lumbar vertebra and MAC was determined after administration of saline and maropitant (1 mg kg(-1)) epidurally. All MAC determinations were done in duplicate. The MAC values were adjusted to sea level and compared using student's t-test. RESULTS: The baseline MAC for sevoflurane was 2.08 ± 0.25%. Intravenous maropitant decreased (p < 0.05) MAC by 16% (1.74 ± 0.17%). In contrast, epidural administration of either saline or maropitant did not change (p > 0.05) the MAC (2.17 ± 0.34% and 1.92 ± 0.12%, respectively). CONCLUSION AND CLINICAL RELEVANCE: Maropitant decreased the MAC of sevoflurane when administered intravenously to dogs but not after epidural administration.

Determination of the sevoflurane sparing effect of methadone in cats.

OBJECTIVE: To determine the magnitude and duration of sevoflurane minimum alveolar concentration (MAC) reduction following a single intravenous (IV) dose of methadone in cats. STUDY DESIGN: Prospective experimental study. ANIMALS: Eight (four females and four males) healthy mixed-breed adult (1-2 years) cats weighing 5.82 ± 0.42 kg. METHODS: Anesthesia was induced and maintained with sevoflurane. Intravenous catheters facilitated administration of methadone and lactated Ringer's solution. After baseline MAC determination in triplicate using a tail clamp technique, 0.3 mg kg(-1) of methadone was administered IV. End-tidal sevoflurane concentration (e'SEVO) was reduced and MAC was redetermined. In an effort to determine the duration of MAC reduction, measurements were repeated in a stepwise manner until MAC values returned to baseline. After the last stimulation, the e'SEVO was increased to 1.2 individual MAC for 15 minutes, then sevoflurane was discontinued and cats were allowed to recover from anesthesia. RESULTS: Baseline sevoflurane MAC was 3.18 ± 0.06%. When compared with baseline the sevoflurane MAC after methadone administration was significantly reduced by 25, 15 and 7% at 26, 76 and 122 minutes, respectively. The final MAC value (3.09 ± 0.07%) determined 156 minutes after methadone administration was not significantly different from baseline. CONCLUSIONS AND CLINICAL RELEVANCE: Intravenous methadone (0.3 mg kg(-1)) significantly decreased MAC of sevoflurane in cats but the effect was short-lived.