Pharmacokinetics and pharmacodynamics of intramuscular alfaxalone in central bearded dragons (Pogona vitticeps): effect of injection site.

OBJECTIVE: To evaluate the pharmacodynamic effects and pharmacokinetics of a single intramuscular (IM) injection of alfaxalone in central bearded dragons (Pogona vitticeps) when injected at a cranial versus a caudal site. STUDY DESIGN: Prospective, masked, randomized crossover study. ANIMALS: A total of 13 healthy bearded dragons weighing 0.48 ± 0.1 kg. METHODS: Alfaxalone (10 mg kg-1) was administered IM to 13 bearded dragons in the triceps muscle (cranial treatment) or the quadriceps muscle (caudal treatment) separated by 4 weeks. Pharmacodynamic variables included movement score, muscle tone score and righting reflex. Blood was obtained from the caudal tail vein using a sparse sampling methodology. Plasma alfaxalone concentrations were determined using liquid chromatography-mass spectrometry, and pharmacokinetic analysis was performed using nonlinear mixed-effects modeling. Differences in variables between injection sites were analyzed using a nonparametric Wilcoxon signed-rank test for paired data with significance set at p ≤ 0.05. RESULTS: Time to loss of righting reflex score was not different, median (interquartile range), between cranial and caudal treatments [8 (5-11) and 8 (4-12) minutes, respectively, p = 0.72]. Time to recovery of righting reflex was also not different between cranial and caudal treatments [80 (44-112) and 64 (56-104) minutes, respectively, p = 0.75]. Plasma alfaxalone concentrations were not significantly different between treatments. The population estimate (95% confidence intervals) for volume of distribution per fraction absorbed was 1.0 (0.79-1.20) L kg-1, clearance per fraction absorbed was 9.6 (7.6-11.6) mL minute-1 kg-1, absorption rate constant was 2.3 (1.9-2.8) minute-1 and elimination half-life was 71.9 (52.7-91.1) minutes. CONCLUSIONS AND CLINICAL RELEVANCE: Regardless of the injection site, IM alfaxalone (10 mg kg-1) produced reliable chemical restraint in central bearded dragons, appropriate for nonpainful diagnostic procedures or anesthetic premedication.

Cuff size, cuff placement, blood pressure state, and monitoring technique can influence indirect arterial blood pressure monitoring in anesthetized bats (Pteropus vampyrus).

OBJECTIVE: Evaluate agreement between 2 non-invasive blood pressure (NIBP) techniques and invasive arterial blood pressure (IBP) in anesthetized bats using various cuff sizes and cuff positioning while also evaluating its performance during hypertension and hypotension. ANIMALS: 8 bats (1.1 ± 0.2 kg). PROCEDURES: Bats were anesthetized with isoflurane in oxygen. NIBP was measured using oscillometric (NIBP-O) and Doppler (NIBP-D) techniques in the pectoral limb (PEC) and pelvic limbs (PEL) using 3 cuff sizes (1, 2, and 3). NIBP measurements were compared with IBP; systolic (SAPinvasive), mean (MAPinvasive), and diastolic arterial blood pressure (DAPinvasive) during normotension, hypertension, and hypotension. Hypotension was induced with isoflurane (3.8 ± 1.2%) and hypertension with norepinephrine (3 ± 0.5 µg/kg/min). Data analysis included Bland-Altman analyses and 3-way ANOVA. Results were reported as mean bias (95% CI). RESULTS: NIBP-O monitor reported 29% errors, and experienced more failures with hypertension, cuff placement on PEC, and using a size 1 cuff. Across states, an agreement between NIBP-D and MAPinvasive with cuff 2 on PEL (-3 mmHg [-8, 1]), and NIBP-D and SAPinvasive with cuff 3 on PEC (2 mmHg [-5, 9 mmHg]) was achieved. NIBP-D over-estimated SAPinvasive and MAPinvasive during hypertension in both limbs with cuffs 1 and 2. Except during hypotension, NIBP-O underestimated MAPinvasive and DAPinvasive using a size 2 cuff on PEL. CLINICAL RELEVANCE: In anesthetized bats, NIBP-O is unreliable for estimating IBP. NIBP-D shows acceptable agreement with MAPinvasive with cuff size 2 on PEL, and with SAPinvasive with cuff size 3 on PEC across a wide range of IBP values.

Successful treatment of prolonged refractory ventricular fibrillation in an anesthetized dog.

OBJECTIVE: To describe a case of successful return of spontaneous circulation in an anesthetized dog that developed spontaneous ventricular fibrillation during CPR that was refractory to multiple defibrillation attempts by utilizing pharmacological antiarrhythmic therapy. CASE SUMMARY: Cardiopulmonary arrest occurred during surgical preparation in a 1-year-old German Shepherd Dog under general anesthesia for fluoroscopic implantation of an Amplatz canine duct occluder for treatment of a patent ductus arteriosus. Pulseless electrical activity was initially diagnosed, and resuscitative efforts were immediately initiated, including basic cardiac life support, discontinuation of anesthesia with administration of reversal agents, and low-dose epinephrine administration (0.01 mg/kg, IV). After 10 minutes of CPR, the patient developed ventricular fibrillation and single-dose monophasic defibrillation attempts of escalating energy were performed. Despite these efforts, return of spontaneous circulation was unable to be achieved. However, administration of magnesium sulfate (20 mg/kg, IV) along with an additional single monophasic defibrillation attempt was successful in achieving return of spontaneous circulation. NEW OR UNIQUE INFORMATION PROVIDED: Under current advanced cardiac life support guidelines, the best resuscitation strategy for refractory ventricular fibrillation, in which the arrhythmia persists despite multiple defibrillation attempts, remains unclear. This is especially true for veterinary patients, where refractory ventricular fibrillation is an uncommon cardiac arrest rhythm. Although guidelines for the use of antiarrhythmic therapy during cardiac arrest are well established in human medicine, evidence-based guidelines to support best practices in companion animals do not exist due to sparse data gathered through experimental studies. Only a few case reports describe successful return of spontaneous circulation following prolonged ventricular fibrillation in clinical veterinary patients. Although the use of magnesium sulfate as an antiarrhythmic agent during refractory ventricular fibrillation has been previously reported in people, this is the first case to our knowledge of refractory ventricular fibrillation in a dog that responded to magnesium sulfate.

Sedation and Anesthesia of Galapagos (Chelonoidis nigra), Aldabra (Aldabrachelys gigantea), and African Spurred Tortoises (Centrochelys sulcata): A Retrospective Review (2009-2019).

Tortoises belong to the taxonomic family Testudinidae, which is considered one of the most imperiled families of the order Testudines. Anesthesia is often required for the medical and surgical management of large tortoises. The objectives of this retrospective study were to review drug regimens used to successfully anesthetize Galapagos (Chelonoidis nigra), Aldabra (Aldabrachelys gigantea) and African spurred (Centrochelys sulcata) tortoises, and to compare the times to effect and to extubation in tortoises administered different premedication protocols. Anesthetic records of giant tortoises admitted to the University of Florida College of Veterinary Medicine between January 2009 and December 2019 were reviewed. A total of 34 tortoises (six Aldabra, 23 Galapagos, and five African spurred) were included, resulting in 64 anesthetic events. Frequently used premedication protocols included an α2-adrenergic agonist and ketamine combined with either midazolam (group α2-adrenergic agonist, midazolam, ketamine, AMK; n = 34), a µ-opioid receptor agonist (group α2-adrenergic agonist, µ-opioid receptor agonist, ketamine, AOK; n = 13), or a µ-opioid receptor agonist and midazolam (group α2-adrenergic agonist, midazolam, µ-opioid receptor agonist, ketamine, AMOK; n = 10). Inhalant anesthetics (isoflurane, n = 21; sevoflurane, n = 23) were frequently used for maintenance of anesthesia following premedication. Out of the 34 total tortoises, 22 had only one anesthetic event, five had two anesthetic events, three had three anesthetic events, and four had four or more anesthetic events. Few adverse effects were observed and there was no mortality reported during the peri-anesthetic period. Sedation and general anesthesia of giant tortoises can be successfully performed with a combination of an α2-adrenergic agonist and ketamine in combination with midazolam and/or a µ-opioid receptor agonist.

The effect of erector spinae plane block on perioperative analgesic consumption and complications in dogs undergoing hemilaminectomy surgery: a retrospective cohort study.

OBJECTIVE: To compare the perioperative use of analgesics and complication rates in dogs administered an erector spinae plane (ESP) block or a traditional opioid-based (OP) treatment as part of analgesic management during hemilaminectomy. STUDY DESIGN: Retrospective cohort study. ANIMALS: Medical records of 114 client-owned dogs. METHODS: General data included demographics, duration of procedure, number of laminae fenestrated, perioperative use of steroid and non-steroidal anti-inflammatory drugs. Intra- and postoperative analgesics used in 48 hours and complications rates were compared between groups. Opioid use was expressed in morphine equivalents [ME (mg kg-1)]. Continuous data were compared using the Mann-Whitney U test and incidence of events with a Fisher's exact tests. Multiple linear regression was used to evaluate association between perioperative ME consumption (dependent variable) with other independent variables. Data are presented as median (range). Differences were considered significant when p < 0.05. RESULTS: Group ESP comprised 42 dogs and group OP 72 dogs. No differences were observed in the general data. Intraoperative ME was 0.65 (0.20-3.74) and 0.79 (0.19-5.60) mg kg-1 in groups ESP and OP, respectively (p = 0.03). Intraoperative infusion of lidocaine was administered intravenously (IV) to 23.8% and 68% of groups ESP and OP, respectively (p < 0.0001). Intraoperative infusion of ketamine was administered IV to 21% and 40% of groups ESP and OP, respectively (p = 0.04). Regression analysis revealed the ESP block as the only independent variable affecting the perioperative ME consumption. Pharmacological intervention to treat cardiovascular complications was administered to 21.4% and 47.2% of dogs in groups ESP and OP, respectively (p = 0.008). There were no differences in postoperative complication rates. CONCLUSIONS AND CLINICAL RELEVANCE: ESP block was associated with reduced perioperative opioid consumption, intraoperative adjuvant analgesic use and incidence of pharmacological interventions to treat cardiovascular complications in dogs undergoing hemilaminectomy.

A DESCRIPTION OF ARTERIAL BLOOD PRESSURE MEASUREMENT IN TWO SPECIES OF FLYING FOXES (PTEROPUS VAMPYRUS AND PTEROPUS HYPOMELANUS).

Blood pressure assessment is valuable during management of chronic conditions with increased risk of developing hypertension and as a standard practice for anesthetic monitoring. Normal arterial blood pressure values have not been well described in megachiropteran species. Following anesthetic induction and maintenance with isoflurane in oxygen, arterial blood pressure was obtained from the posterior tibial artery of eight large flying foxes (Pteropus vampyrus) and six variable flying foxes (Pteropus hypomelanus), two with structural cardiac disease and four in good clinically health. Normal values reported as a median with interquartile range for systolic, diastolic, and mean (MAP) arterial pressures for P. vampyrus were 101 (94, 107), 69 (57, 80), and 86 (75, 93), respectively. Normal MAP for clinically healthy P. hypomelanus was 86 (67, 93). Placement of P. hypomelanus in a vertical head-down position did not alter blood pressure in clinically healthy bats, but significantly increased MAP in two bats with structural cardiac disease. Arterial catheterization of both the posterior tibial and median arteries in these species was easily performed without major complication.

MOTOR NERVE CONDUCTION VELOCITIES OF THE MEDIAN AND SCIATIC-TIBIAL NERVES IN EIGHT NORMAL LARGE FLYING FOXES ( PTEROPUS VAMPYRUS).

Electrodiagnostic testing is an integral part of the evaluation of the motor unit in many neurologic conditions. Literature about the peripheral nervous system of flying foxes ( Pteropus spp) is sparse, and reference range values for motor nerve conduction velocities in vivo have not been established in Chiropterans. The goals of this study were to determine reference range conduction velocities in flying fox for the thoracic and pelvic limb nerve. Eight Pteropus vampyrus, large flying foxes, of varying ages and gender underwent nerve conduction studies of the median nerve and sciatic-tibial nerve. Mean (SD) conduction velocity values were 49.8 (12.7) m/sec for the median nerve and 42.1 (10.2) m/sec for the sciatic-tibial nerve. Median nerve conduction velocities were not significantly faster than sciatic-tibial nerve conduction velocities, although a trend was seen. Differences by sex or age class were not statistically significant. It was also noted that flying foxes rapidly lose body heat under general anesthesia.

INHALANT ANESTHETIC RECOVERY FOLLOWING INTRAMUSCULAR EPINEPHRINE IN THE LOGGERHEAD SEA TURTLE ( CARETTA CARETTA).

Prolonged anesthetic recovery time is a common complication of chelonian inhalant anesthesia and may be exacerbated by right-to-left intracardiac shunting of blood. Epinephrine may decrease intracardiac shunting, which may shorten anesthetic recovery time. The study objective was to assess inhalant anesthetic recovery time following intramuscular epinephrine compared with saline in the loggerhead sea turtle ( Caretta caretta). With the use of a prospective, randomized, blinded, crossover design with a 1-wk washout period, six turtles were anesthetized with intravenous (IV) alfaxalone 3 mg/kg, orotracheally intubated, manually ventilated with 3.5% isoflurane inhalant in 100% oxygen for 90 min, and administered either intramuscular (IM) epinephrine 0.1 mg/kg or IM saline 0.1 ml/kg. Isoflurane administration was immediately discontinued and turtles were manually ventilated with room air until extubation. Physiologic variables, sedation scores, end-tidal carbon dioxide (ETCO2) and isoflurane (ETISO) concentrations, time to first movement, and time to extubation were recorded and two-time-point venous blood gas analyses performed. Data were compared with the use of paired t-tests and repeated-measures analyses of variance (ANOVA) ( P < 0.05). No morbidity, mortality, or adverse events occurred. ETCO2 and ETISO did not significantly change over time during the isoflurane delivery period ( P = 0.990). Mean time to first movement was significantly faster following epinephrine (69.24 ± 12.28 min) compared with saline (87.71 ± 27.05 min, P = 0.047). Although differences were not statistically significant ( P = 0.133), time to extubation was at least 30 min faster (31-123 min) in 4/6 turtles following epinephrine compared with saline. Intramuscular epinephrine significantly reduces time to first movement during isoflurane anesthetic recovery in loggerhead sea turtles.

INTRAMUSCULAR EPINEPHRINE RESULTS IN REDUCED ANESTHETIC RECOVERY TIME IN AMERICAN ALLIGATORS (ALLIGATOR MISSISSIPPIENSIS) UNDERGOING ISOFLURANE ANESTHESIA.

Inhalants are commonly used to anesthetize reptiles, but volatile anesthetics have been associated with prolonged recovery times. The objective of this study was to determine the effects of intramuscular (IM) epinephrine on anesthetic recovery times following isoflurane anesthesia in a population of subadult American alligators ( Alligator mississippiensis ). In this prospective randomized crossover study, five clinically healthy alligators were anesthetized for 90 min with the use of isoflurane. Alligators were randomly assigned into one of two treatment groups: Group E received IM epinephrine (0.1 mg/kg), and Group S received an equal volume of 0.9% saline administered after isoflurane was discontinued. Time from the end of inhalant administration to return of spontaneous ventilation, return of the palpebral reflex, movement in response to a standardized toe pinch, and spontaneous movement was recorded. The time of extubation was noted and occurred following the return of spontaneous ventilation and movement. Pulse rate, surface body temperature, and airway gases including expiratory and inspiratory isoflurane concentrations and end-tidal carbon dioxide were measured every 5 min throughout the study. The time from the end of anesthesia to extubation was significantly faster in Group E (51.2 ± 16.7 min) compared to Group S (107.4 ± 43.7 min). Pulse rate was significantly higher within the first 15 min following epinephrine injection compared to the saline group at these time points. Therefore, IM epinephrine administered at the end of general anesthesia can significantly hasten anesthetic recovery from isoflurane in alligators.

EPINEPHRINE OR GV-26 ELECTRICAL STIMULATION REDUCES INHALANT ANESTHESTIC RECOVERY TIME IN COMMON SNAPPING TURTLES (CHELYDRA SERPENTINA).

Prolonged anesthetic recovery times are a common clinical problem in reptiles following inhalant anesthesia. Diving reptiles have numerous adaptations that allow them to submerge and remain apneic for extended periods. An ability to shunt blood away from pulmonary circulation, possibly due to changes in adrenergic tone, may contribute to their unpredictable inhalant anesthetic recovery times. Therefore, the use of epinephrine could antagonize this response and reduce recovery time. GV-26, an acupuncture point with reported ß-adrenergic and respiratory effects, has reduced anesthetic recovery times in other species. In this prospective randomized crossover study, six common snapping turtles (Chelydra serpentina) were anesthetized with inhalant isoflurane for 90 min. Turtles were assigned one of three treatments, given immediately following discontinuation of isoflurane: a control treatment (0.9% saline, at 0.1 ml/kg i.m.), epinephrine (0.1 mg/kg i.m.), or acupuncture with electrical stimulation at GV-26. Each turtle received all treatments, and treatments were separated by 48 hr. Return of spontaneous ventilation was 55% faster in turtles given epinephrine and 58% faster in the GV-26 group versus saline (P < 0.001). The times to movement and to complete recovery were also significantly faster for both treatments than for saline (P < 0.02). Treated turtles displayed increases in temperature not documented in the control (P < 0.001). Turtles administered epinephrine showed significantly increased heart rates and end-tidal CO(2) (P < 0.001). No adverse effects were noted in the study animals. The mechanisms of action were not elucidated in the present investigation. Nevertheless, the use of parenteral epinephrine or GV-26 stimulation in the immediate postanesthetic period produces clinically relevant reductions in anesthetic recovery time in common snapping turtle. Further research is necessary to evaluate the effects of concurrent GV-26 and epinephrine administration and to assess responses in other reptilian species.

Use of a perfusion index to confirm the presence of sciatic nerve blockade in dogs.

OBJECTIVES: To evaluate perfusion index (PI) as a determinant of regional nerve block success following sciatic nerve blockade with bupivacaine in dogs undergoing stifle surgery. STUDY DESIGN: Prospective clinical trial. ANIMALS: Ten adult dogs, aged 5.6 ± 2.6 years and weighing 36.9 ± 16.8 kg, undergoing a tibial plateau leveling osteotomy. METHODS: Dogs were premedicated with acepromazine (0.03 mg kg-1 ) and hydromorphone (0.1 mg kg-1 ) intramuscularly, and anesthetized with propofol (up to 4 mg kg-1 ) intravenously and isoflurane in oxygen. An ultrasound-guided femoral and sciatic (F+S) nerve block was performed on the surgical limb with bupivacaine (0.75%), 0.2 mL kg-1 at the femoral site and 0.3 mL kg-1 at the sciatic site, with a maximum volume of 10 mL per site. Physiological variables were recorded every 5 minutes throughout anesthesia. A pulse co-oximeter probe was placed between the third and fourth digits of both pelvic limbs, and the PI was recorded 5 minutes before infiltration with bupivacaine, immediately afterwards, and every 5 minutes for 30 minutes. Motor nerve conduction velocity (MNCV) of the sciatic nerve was performed on the surgical limb 5 minutes before and 20 minutes after bupivacaine administration to confirm nerve block. RESULTS: The PI of the surgical limb was significantly greater than the contralateral pelvic limb at 10 minutes (p = 0.03) and 15 minutes (p < 0.01) after F+S nerve blockade. The MNCV performed after sciatic nerve blockade revealed a functional motor blockade for all dogs. There were no significant changes in physiological variables. CONCLUSIONS AND CLINICAL RELEVANCE: The PI provided a reliable indication of successful sciatic nerve blockade in the clinical patients in this study. No increase in the PI by 15 minutes after bupivacaine administration around the sciatic nerve could indicate partial or total failure of anesthetic blockade.

Effects of premedication with sustained-release buprenorphine hydrochloride and anesthetic induction with ketamine hydrochloride or propofol in combination with diazepam on intraocular pressure in healthy sheep.

OBJECTIVE: To determine the effects of diazepam combined with ketamine hydrochloride or propofol for induction of anesthesia (IOA) following premedication with sustained-release buprenorphine hydrochloride (SRB) on intraocular pressure (IOP) in sheep. ANIMALS: 20 healthy adult sheep. PROCEDURES: Diazepam with ketamine or propofol was given IV to each of 10 sheep after premedication with SRB (0.01 mg/kg, SC); after > 4 weeks, each sheep received the other induction combination with no premedication. For both eyes, IOPs were measured before premedication (if given), 10 minutes prior to (baseline) and immediately following administration of ketamine or propofol (time of IOA), after endotracheal intubation, and 5 minutes after IOA. Peak end-tidal P(CO2), globe position, and pupillary diameter were also analyzed. RESULTS: Data were not available for all sheep for all anesthetic episodes. Propofol-diazepam administration alone had no significant effect on IOP, whereas there was a significant decrease in IOP immediately following ketamine-diazepam administration alone. At 5 minutes after ketamine-diazepam administration, SRB-premedicated sheep had significantly higher IOP than unpremedicated sheep. Intraocular pressure was significantly higher at baseline, at intubation, and 5 minutes after IOA in SRB-premedicated sheep receiving propofol-diazepam, compared with unpremedicated sheep. Peak end-tidal P(CO2) at intubation was significantly higher in SRB-premedicated sheep. For sheep receiving either anesthetic treatment, IOPs did not differ significantly with or without SRB premedication. Globe position or pupillary diameter and IOP were not significantly related at any time point. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggested that both ketamine-diazepam and propofol-diazepam combinations were suitable for IOA without increasing IOP in sheep. The use of SRB should be avoided in sheep when increases in IOP are undesirable.