Kate M. Bailey

The efficacy of alfaxalone for immersion anesthesia in koi carp (Cyprinus carpio)

OBJECTIVE To characterize the physiologic and behavioral effects of a single induction dose and two maintenance doses of alfaxalone delivered by water immersion in the anesthesia of koi (Cyprinus carpio). STUDY DESIGN Prospective, within-subject complete crossover design. ANIMALS Six adult koi (Cyprinus carpio) with a median body weight of 344.5 g (range 292.0-405.0 g). METHODS Koi were immersed in water containing 10 mg L(-1) alfaxalone until immobile and then maintained with alfaxalone at either 1 or 2.5 mg L(-1) via a recirculating water system. Times for anesthetic induction and recovery periods were recorded. Physiologic and blood gas parameters were evaluated before, during and after the anesthetic trial. Response to noxious stimuli was also assessed. RESULTS Median anesthesia induction time for all fish was 5.4 minutes. Median recovery time was 11.8 and 26.4 minutes in the 1.0 and 2.5 mg L(-1) doses, respectively, which were significantly different (p = 0.04). Cessation of opercular movement occurred in 0/6 and 4/6 fish exposed to 1.0 and 2.5 mg L(-1) dose respectively. No difference was observed in median heart rate over the duration of the anesthetic events. Response to noxious stimulation was 4/6 and 0/6 in the 1.0 and 2.5 mg L(-1) doses respectively. Oxygenation and ventilation did not change during the experiment, but there was a significant decrease in blood pH along with an increase in blood lactate concentration. CONCLUSION AND CLINICAL RELEVANCE Administration of alfaxalone, via water immersion, as an induction and maintenance anesthesia agent provided rapid and reliable anesthesia of koi with no mortality. The maintenance dose of 2.5 mg L(-1) was sufficient to prevent response to noxious stimuli but was associated with a clinically relevant depression in opercular rate.

Physiologic and biochemical assessments of koi (Cyprinus carpio) following immersion in propofol.

OBJECTIVE To determine efficacy of propofol as an immersion agent to induce general anesthesia in koi (Cyprinus carpio). DESIGN Prospective, crossover study. ANIMALS 10 adult koi (mean ± SD weight, 325 ± 81 g). PROCEDURES Koi were exposed to each of 4 concentrations of propofol (1, 2.5, 5, and 10 mg/L) with a 1-week washout period between trials. In a subsequent trial, koi were anesthetized with propofol (5 mg/L) and anesthesia was maintained with propofol (3 mg/L) for 20 minutes. Response to a noxious stimulus was assessed by means of needle insertion into an epaxial muscle. RESULTS At a propofol concentration of 1 mg/L, koi were sedated but never anesthetized. At propofol concentrations of 2.5, 5, and 10 mg/L, mean ± SD anesthetic induction times were 13.4 ± 3.3, 3.8 ± 1.1, and 2.3 ± 0.9 minutes, respectively; mean recovery times were 12.9 ± 8.3, 11.0 ± 6.3, and 18.1 ± 13.0 minutes; mean heart rates were 57 ± 25, 30 ± 14, and 22 ± 14 beats/min; mean opercular rates were 58 ± 18, 68 ± 15, and 48 ± 22 beats/min; and 1 of 10, 2 of 10, and 0 of 10 fish responded to needle insertion. All fish recovered satisfactorily. Following 20 minutes of anesthesia, 2 fish had recovery times > 4 hours and 1 fish died. CONCLUSIONS AND CLINICAL RELEVANCE Immersion in propofol at concentrations ≥ 2.5 mg/L induced general anesthesia in koi. Maintenance of anesthesia with propofol for 20 minutes was associated with prolonged recovery times in 2 of 9 and death in 1 of 9 koi.

ALFAXALONE ANESTHESIA IN BULLFROGS (LITHOBATES CATESBEIANA) BY INJECTION OR IMMERSION

This project evaluated alfaxalone, a neurosteroid, as an anesthetic in bullfrogs. Eight adult bullfrogs (Lithobates catesbeiana), averaging 593 g (411-780 g) each, were used in a crossover design. Frogs were administered alfaxalone i.m. at 10, 12, 15, or 17.5 mg/kg with a 1-wk washout. Following injection, time to recumbency, first limb movement following induction, and recovery were recorded. Respiratory rate was recorded following injection and then every 15 min following induction. Heart rate was assessed via Doppler every 15 min following induction. At 20 and 40 min, a 25-ga needle was inserted in a thigh muscle to assess response to noxious stimuli. Frogs were also immersed in 2 g/L of alfaxalone for up to 30 min and similarly assessed. At dosages of 10, 12, 15, and 17.5 mg/kg, the median time to recumbency was 15.4, 12.6, 12.3, and 6.6 min, respectively. At dosages of 10, 12, 15, and 17.5 mg/kg, median time to first limb movement was 68.5, 77.5, 89.0, and 115 min, respectively. At dosages of 10, 12, 15, and 17.5 mg/kg, median time to recovery was 90, 68.5, 124.5, 115 min, respectively. Following induction, at 10, 12, 15, and 17.5 mg/kg, median heart rate was 42, 40, 40, and 42, respectively; and median respiratory rate was 44, 36, 29, and 35, respectively. Following administration of 10, 12, 15, and 17.5 mg/ kg, 8/8, 6/8, 7/8, and 8/8 frogs, respectively, responded to needle insertion. None of the frogs dosed by immersion became anesthetized. Intramuscular alfaxalone produced immobilization in frogs but did not provide sufficient anesthesia to prevent response to noxious stimuli. Alfaxalone immersion at 2 g/L for 30 min did not produce immobilization or anesthesia.

Alfaxalone as an intramuscular injectable anesthetic in koi carp (Cyprinus carpio).

Abstract:  Fish are commonly anesthetized with MS-222 (tricaine methanesulfonate), a sodium-channel-blocker used as an immersion anesthetic, but its mechanism of action as a general anesthetic is uncertain. Alfaxalone is a neurosteroid that acts at the GABAA receptors. Alfaxalone has been evaluated and was deemed successful as an immersion agent in koi carp. Alfaxalone is an effective intramuscular anesthetic in multiple species. A reliable intramuscular anesthetic in fish would be useful in multiple settings. The purpose of this study was to investigate alfaxalone as an intramuscular injectable anesthetic agent in koi carp (Cyprinus carpio). Eight koi carp were utilized in a crossover design. In each trial, six fish received 1 mg/kg, 5 mg/kg, or 10 mg/kg of alfaxalone intramuscularly. They were assessed every 15 min for opercular rate and sedation score. The sedation score was based on a visual scale from 0 to 5, 0 indicating no response and 5 indicating absent righting reflex and anesthesia. Anesthetized koi were placed on a fish anesthesia delivery system (FADS). Time to anesthesia/recovery was recorded and heart rate was recorded every 15 min. Anesthesia was achieved in 0/6, 1/6, and 5/6 fish at 1, 5, and 10 mg/kg, respectively. Duration of anesthesia for one fish at 5 mg/kg was 2 hr. At 10 mg/kg, median anesthesia duration was 6.5 (3–10) hr. At 10 mg/kg, prolonged apnea (2–3 hr) was observed in 3/6 fish, 2/3 died under anesthesia, and 1/3 recovered 10 hr post-injection. Median peak sedation scores were 1.5, 2.5, and 5, at 1, 5, and 10 mg/kg, respectively. A dosage of 10 mg/kg alfaxalone resulted in 33% mortality. The duration of anesthesia and opercular rate were unpredictable. Due to variation in response despite consistent conditions, as well as risk of mortality, intramuscular alfaxalone cannot be recommended for anesthesia in koi carp.

EFFICACY OF ALFAXALONE FOR INTRAVASCULAR ANESTHESIA AND EUTHANASIA IN BLUE CRABS (CALLINECTES SAPIDUS)

The objective of this study was to characterize the behavioral effects and changes in heart rate of four doses of alfaxalone delivered by intravascular injection to blue crabs (Callinectes sapidus). Thirty (male, n = 27; female, n = 3) blue crabs were randomly assigned to one of four treatment groups of alfaxalone: eight animals were assigned to each of the 5-, 10-, and 15-mg/kg treatment groups, and the remaining six animals were assigned to the 100-mg/kg group. Times for anesthetic induction and recovery periods were recorded. Righting reflex, defensive posturing, and heart rate were evaluated before, during, and after the anesthetic trial. Anesthesia was induced in all 14 animals consolidated into the high-dosage group (15 mg/kg [n = 8] and 100 mg/kg [n = 6]), which was significantly greater than 8 of 16 animals in the low-dosage group (5 mg/kg [n = 2] and 10 mg/kg [n = 6]). Median anesthesia induction time for all crabs was 0.4 min, with no significant difference in induction time between groups observed. Median recovery time was 9.4 min (n = 2), 6.1 min (n = 5), 11.3 min (n = 8), and 66.1 min (n = 5) for the 5-, 10-, 15-, and 100-mg/kg groups, respectively. Recovery times were significantly longer for crabs exposed to an induction dose of 100 mg/kg compared with the 10- and 15-mg/kg induction doses. A significant decrease in the median heart rate was observed between the baseline value and that observed at both induction and 5 min postinjection in the 100-mg/kg dose trial. Two mortalities were observed during the anesthesia trials (n = 1, 10 mg/kg; n = 1, 100 mg/kg), both associated with the autotomization of limbs. In summary, the intravascular administration of alfaxalone at 15 mg/kg provided rapid and reliable sedation, whereas alfaxalone administered at 100 mg/kg produced rapid and long lasting anesthesia.

Evaluation of the effects of tricaine methanesulfonate on retinal structure and function in koi carp (Cyprinus carpio)

OBJECTIVE To determine whether repeated exposure to clinically relevant concentrations of tricaine methanesulfonate (MS-222) would alter retinal function or induce histologically detectable retinal lesions in koi carp (Cyprinus carpio). DESIGN Prospective, controlled, experimental study. ANIMALS 18 healthy koi carp. PROCEDURES 2 fish were euthanized at the start of the study, and eyes were submitted for histologic evaluation as untreated controls. Anesthesia was induced in the remaining fish with 200 mg of MS-222/L and maintained with concentrations of 125 to 150 mg/L for a total exposure time of 20 minutes daily on 1 to 13 consecutive days. On days 1, 7, and 13, electroretinography of both eyes was performed in all fish remaining in the study, and 2 fish were euthanized immediately after each procedure for histologic evaluation of the eyes. Median b-wave amplitudes were compared among study days for right eyes and for left eyes via 1-way repeated-measures ANOVA with a Bonferroni correction for multiple comparisons. RESULTS Median b-wave amplitudes on days 1, 7, and 13 were 17.7, 20.9, and 17.6 μV, respectively, for right eyes and 15.1, 16.9, and 14.3 μV, respectively, for left eyes. No significant differences in b-wave amplitudes were detected among study days. No histopathologic abnormalities were identified in the retinas of any fish treated with MS-222 or in control fish. CONCLUSIONS AND CLINICAL RELEVANCE Short-term exposure of koi carp to clinically relevant concentrations of MS-222 daily for up to 13 days was not associated with changes in retinal structure or function as measured in this study.

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

Abstract 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.

Recovery of horses from general anesthesia after induction with propofol and ketamine versus midazolam and ketamine

OBJECTIVE To evaluate quality of recovery from general anesthesia in horses after induction with propofol and ketamine versus midazolam and ketamine. DESIGN Prospective randomized crossover study. ANIMALS 6 healthy adult horses. PROCEDURES Horses were premedicated with xylazine (1.0 mg/kg [0.45 mg/lb], IV), and general anesthesia was induced with midazolam (0.1 mg/kg [0.045 mg/lb], IV) or propofol (0.5 mg/kg [0.23 mg/lb], IV), followed by ketamine (3.0 mg/kg [1.36 mg/lb], IV). Horses were endotracheally intubated, and anesthesia was maintained with isoflurane. After 60 minutes, horses were given romifidine (0.02 mg/kg [0.009 mg/lb], IV) and allowed to recover unassisted. Times to first movement, sternal recumbency, and standing and the number of attempts to stand were recorded. Plasma concentrations of propofol or midazolam were measured following induction and immediately before recovery. Recovery quality was scored by 3 graders with a recovery rubric and a visual analog scale. RESULTS Number of attempts to stand was significantly lower when horses received propofol (median, 2; range, 1 to 3) than when they received midazolam (median, 7.5; range, 3 to 16). For both the recovery rubric and visual analog scale, recovery quality was significantly better when horses received propofol than when they received midazolam. Plasma drug concentration at recovery, as a percentage of the concentration at induction, was significantly lower when horses received propofol than when they received midazolam. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that for horses undergoing short (ie, 60 minutes) periods of general anesthesia, recovery quality may be better following induction with propofol and ketamine, compared with midazolam and ketamine.