Electrophysiologic Study of a Method of Euthanasia Using Intrathecal Lidocaine Hydrochloride Administered during Intravenous Anesthesia in Horses

Interrupted Lives: Welfare Considerations in Wildlife Rehabilitation

Each year in the United States, thousands of sick, injured, or displaced wild animals are presented to individuals or organizations who have either a federal or state permit that allows them to care for these animals with the goal of releasing them back to the wild. The purpose of this review is to demonstrate the complexity of considerations rehabilitators and veterinarians face while trying to optimize the welfare of wild animals in need of care and rehabilitation. The process of rehabilitation is inherently stressful for wildlife. Maintaining an animal's welfare during the rehabilitation process-from initial contact and tria+ge to the animal's euthanasia, release, or captive placement-requires deliberate, timely and humane decision making. The welfare of wild animals can be improved by preventing human-related causes of admission, providing resources and support for wildlife rehabilitation (almost all rehabilitation in the United States is privately funded and access to veterinary care is often limited); further developing evidence-based wildlife rehabilitation methods and welfare measures, attracting more veterinary professionals to the field, harmonizing regulatory oversight with standards of care, training, and accountability, and increasing public education.

EVALUATION OF INTRACARDIAC ADMINISTRATION OF POTASSIUM CHLORIDE, IVERMECTIN, OR LIDOCAINE HYDROCHLORIDE FOR EUTHANASIA OF ANESTHETIZED BLUE CRABS (CALLINECTES SAPIDUS)

Methods to anesthetize and euthanize aquatic invertebrates have proven unreliable in decapods; thus studies to optimize euthanasia techniques for crustaceans are needed. Study objectives were to evaluate efficacy of intracardiac potassium chloride (KCl), ivermectin, or lidocaine hydrochloride (HCl) for euthanasia of anesthetized blue crabs (Callinectes sapidus). Twenty adult male crabs (n = 5/group) were immersed in 500 mg/L eugenol for 5 min beyond loss of the righting reflex and then randomly administered intracardiac 10 mEq/kg KCl (333 mg/mL), 5 mg/kg ivermectin (10 mg/ml), 100 mg/kg lidocaine hydrochloride (HCl) (20 mg/ml), or 5 ml/kg saline (0.9%). Serial heart rate assessments were made using a Doppler probe placed over the dorsum, and times to loss of righting reflex, Doppler sound cessation, and/or recovery were recorded. Median (range) time to loss of righting reflex was 32 (17-57) min. One crab in all groups, except lidocaine HCl, had no detectable Doppler sounds prior to injection. In the remaining crabs, Doppler sound cessation occurred in 4/4, 4/4, 4/5, and 0/4 crabs administered KCl, ivermectin, lidocaine HCl, and saline, respectively. Median (range) time to Doppler sound cessation was 30 (0-55), 18 (16-28), and 50 (0-90) s in KCl, ivermectin, and lidocaine HCl groups, respectively. Tonic limb movements were observed in 5/5 KCl-treated crabs. Median (range) time to recovery was 180 (115-345) and 300 m in four saline-treated crabs and one lidocaine HCl-treated crab, respectively. Intracardiac KCl at 10 mEq/kg and ivermectin at 5 mg/kg were effective, rapid methods for euthanasia of anesthetized blue crabs.

Potassium penicillin and gentamicin pharmacokinetics in healthy conscious and anesthetized horses

OBJECTIVE

To determine the effects of general anesthesia on the safety and efficacy of co-administered potassium penicillin G (PEN) and gentamicin (GENT) in horses.

STUDY DESIGN

Nonrandomized crossover.

ANIMALS

Six adult, Thoroughbred horses.

METHODS

Horses were administered PEN (22 000 IU/kg IV) and GENT (6.6 mg/kg IV). Plasma samples were collected over a 6 h period and synovial fluid was collected at 30 min and 6 h respectively. Drug administration and sample collection protocols were repeated after at least a 48 hour washout period and induction of anesthesia using xylazine/ketamine and maintenance with isoflurane gas. Drug concentrations were determined using ultrapressure liquid chromatography with mass spectrometry. A 2-compartment model was used to determine pharmacokinetics and differences were determined between conscious and anesthetized horses using paired t-tests (significance P < .05).

RESULTS

Potassium penicillin g and GENT had higher minimum plasma concentrations (PEN 0.44 vs. 0.11 μg/mL, P = .002; GENT 3.0 vs. 1.9 μg/mL, P = .009), longer half lives (PEN 71 vs. 59 min, P = .018; GENT 149 vs. 109 min, P = .038), and slower clearances (PEN 3.41 vs. 5.1 mL/kg/min, P = .005; GENT 1.18 vs. 1.48 mL/kg/min, P = .028) in anesthetized horses vs. conscious horses. The PEN concentrations remained above the breakpoint minimum inhibitory concentration (MIC, 0.5 μg/mL) for 332 min in anesthetized vs. 199 min in conscious horses. The GENT concentrations reached 10 times higher than the breakpoint MIC (2 μg/mL) in all horses and were maintained for 58 vs. 59 min in anesthetized and conscious states, respectively. Synovial fluid concentrations were higher in conscious horses vs. anesthetized horses at 30 min for PEN (7.0 vs. 0.93 μg/mL, P < .001) and 30 (5.3 μg/mL vs. 0.79 μg/mL, P < .001) and 360 min (3.4 vs. 1.82 μg/mL, P < .003) for GENT.

CONCLUSION

General anesthesia resulted in lower intrasynovial concentrations and delayed clearance of PEN/GENT in horses.

CLINICAL SIGNIFICANCE

Redosing healthy anesthetized horses with PEN prior to 4-5 h is not necessary. When administered to anesthetized horses, intravenous PEN/GENT may not reach adequate intrasynovial concentrations to treat or prevent common pathogens. The doses or dosing intervals of antimicrobials administered to horses undergoing anesthesia may need to be adjusted to ensure maintenance of safe and effective plasma concentrations.

Lessons and Recommendations from a Pentobarbital Shortage; US and Canada 2021

In 2021, a shortage in the supply of the euthanasia drug pentobarbital sodium affected animal care professionals around the world, including in the United States and Canada. Pentobarbital sodium is the drug of choice for companion animal euthanasia in both countries. The decreased availability of pentobarbital sodium affected a number of animal care industries, forcing conservation of the drug and the use of alternative methods and other agents to facilitate humane death for all manner of animal species. Veterinary medical groups, laboratory research institutions, and the animal sheltering industry worked together to identify the best path forward to maintain routine euthanasia practices and to protect the welfare of animals. This article aims to explore the reasons behind the shortage and to highlight the necessary responses and adjustments made in order to continue providing euthanasia services in North America. Recommendations for handling future pentobarbital shortages are included.

When All Else Fails: Alternative Methods of Euthanasia

Barbiturate overdose as a method of euthanasia is becoming unacceptable. This has made alternative methods of euthanasia very important. Gunshot or captive bolt euthanasia is among methods that are acceptable, but they may not be esthetically acceptable. This has led to the use of other methods of euthanasia. Inducing anesthesia prior to euthanasia offers an easier method of control. Adjunctive techniques using intravenous potassium or magnesium salts administered intravenously and intracardiac administration of potassium chloride or intrathecal lidocaine offer alternatives that work well and are more environmentally safer than barbiturates. Pithing and exsanguination are also environmentally safer but may not be as esthetically acceptable as the other methods.

Common and Alternative Routes of Euthanasia Solution Administration

There are many acceptable routes of euthanasia solution administration in companion animals. The most common ones are those with consistent use and success, and that align with what is best for the patient, client, and veterinary team. Common injection sites include the venous, hepatic, and renal systems. The barbiturate drugs are in consistent use today, but other drugs may be better given the setting and circumstances at the time. Alternative techniques are available, but only reached for when other more suitable routes of administration are not ideal.

Assessment of humaneness using gunshot targeting the brain and cervical spine for cervid depopulation under field conditions

Population reduction or eradication of domestic or non-domestic species may be required to address their impacts on the environment, other species, or human interests. Firearms are often used to accomplish these practical management objectives, and there is increased concern that the methods used may compromise animal welfare. We document the accuracy and humaneness of gunshot placement to the brain and cervical vertebrae of Philippine deer (Rusa marianna) on Guam during depopulation activities as a model for meeting AVMA standards of euthanasia under field conditions (e.g., animal is not in hand). Deer were shot with a .223 caliber rifle from 10-125 m and approached immediately (<20 s) for assessment. A subset of adult deer was further evaluated for physiological responses including cessation of heart rate, respiration, ocular reflexes, and post-mortem spasms. All deer shot in the brain (n = 132) and upper cervical spine (C1-C3; n = 18) died immediately due to the destruction of the brain or spinal tissue. Shot placements were all within 1.9 cm of the point of aim (i.e., the center of the target region). The accuracy and immediate insensibility resulting from targeting of C1-C3 demonstrates that this is an alternative target site when animal positioning is not optimal for targeting the brain, or there is a need to preserve brain tissue (e.g., Chronic Wasting Disease testing). While targeting of C4 -C7 vertebrae (n = 6) was accurate and resulted in immediate incapacitation, the failure to produce immediate insensibility does not support the use of this shot placement when upper cervical or brain shot placement is an option. It is reasonable to achieve sufficient accuracy to target the brain or upper cervical vertebrae of deer under field conditions and meet standards of euthanasia while accomplishing management objectives.

Investigation of Known Genetic Mutations of Arabian Horses in Egyptian Arabian Foals with Juvenile Idiopathic Epilepsy

Background

The carrier status of lavender foal syndrome (LFS), cerebellar abiotrophy (CA), severe combined immunodeficiency (SCID), and occipitoatlantoaxial malformation (OAAM1) in foals with juvenile idiopathic epilepsy (JIE) is unknown.

Hypothesis/Objectives

To determine the carrier status of LFS, CA, SCID, and OAAM1 in foals with JIE.

Animals

Ten foals with JIE.

Materials and Methods

Archived DNA samples were tested for known genetic mutations causing LFS, CA, SCID, and OAAM1. The inclusion criteria consisted of having been diagnosed with JIE by ruling out other causes of seizures in foals and supported by electroencephalographic examination.

Results

Ten Egyptian Arabian horses (5 females and 5 males) were phenotyped as foals with JIE by electroencephalography (EEG). All foals were negative for the genetic mutations that cause LFS, CA, SCID, and OAAM1 except for 1 foal that was a carrier of CA.

Conclusions and Clinical Importance

Juvenile idiopathic epilepsy of Egyptian Arabian foals and LFS appear to be phenotypically and genetically distinct disorders. There was no apparent association between JIE and LFS, CA, SCID, and OAAM1.

Drug Residues after Intravenous Anesthesia and Intrathecal Lidocaine Hydrochloride Euthanasia in Horses

Background

Intrathecal lidocaine hydrochloride under general anesthesia has been used as an alternative method of euthanasia in equids. Carnivore, scavenger, and even human consumption of horse meat from carcasses have been anecdotally reported in rural areas after this method of euthanasia. The presence of drug residues in horse meat has not been investigated.

Hypothesis/Objectives

To investigate if drug residues are found in horse tissues and determine their concentrations.

Animals

Of 11 horses requiring euthanasia for medical reasons.

Methods

Prospective descriptive study. Horses were anesthetized with total IV dose of xylazine (mean, 2.5 mg/kg), midazolam (0.1 mg/kg), and ketamine hydrochloride (mean, 5.8 mg/kg). An atlanto‐occipital cisterna centesis for the collection of cerebrospinal fluid (CSF) and administration of lidocaine hydrochloride (4 mg/kg) was performed. Blood samples for both serum and plasma, skeletal muscle (triceps brachii, gluteus medius), and CSF were collected for the determination of drug residues. Frozen skeletal muscle available from 5 additional horses that received standard dosages of drugs for short‐term anesthesia (xylazine 1.1 mg/kg, midazolam 0.1 mg/kg, and ketamine 2.2 mg/kg) also were analyzed.

Results

Drug residues were found in the tissues of all horses, but at extremely low concentrations.

Conclusions and Clinical Importance

Euthanasia by administration of lidocaine intrathecally to horses under IV anesthesia poses a low risk of toxicity to carnivores and scavengers that might consume muscle tissue from a carcass in which this protocol has been used.

Cardiovascular, respiratory and metabolic responses to apnea induced by atlanto-occipital intrathecal lidocaine injection in anesthetized horses

OBJECTIVE

To determine physiologic responses to apnea-induced severe hypoxemia in anesthetized horses.

STUDY DESIGN

Prospective experimental study.

ANIMALS

Six university-owned horses with a median (range) body weight of 500 (220-510) kg and aged 13.5 (0.8-24.0) years scheduled for euthanasia.

METHODS

Xylazine-midazolam-ketamine-anesthetized horses breathing room air spontaneously were instrumented with a facial artery catheter for pressure measurement and blood sampling, and were made apneic with atlanto-occipital intrathecal lidocaine (4 mg kg^-1 ). Cardiopulmonary, biochemical and hematologic variables were recorded before (baseline) and every minute for 10 minutes after lidocaine injection.

RESULTS

PaO₂ values were: baseline, 55 mmHg (7.3 kPa); 1 minute, 28 mmHg (3.8 kPa); 2 minutes, 18 mmHg (2.4 kPa); 3 minutes, 15 mmHg (2.0 kPa), and 4-10 minutes, (8-11 mmHg (1.1-1.5 kPa). PaCO₂ values were: baseline, 50 mmHg (6.7 kPa); 1 minute, 61 mmHg (8.1 kPa), and 2-10 minutes, 64-66 mmHg (8.5-8.8 kPa). Base excess values at baseline, 1 minute and 2-10 minutes were 5.3 mmol L^-1 , 6.5 mmol L^-1 and 7.0-8.1 mmol L^-1 , respectively. Pulse rates at baseline, 1 minute and 2-7 minutes were 36, 53 and 54-85 beats minute^-1 , respectively. Asystole occurred at 8 minutes. Pulse pressures were 50 mmHg at baseline and 1 minute, and 39 mmHg, 31 mmHg, 22 mmHg, 17 mmHg and 1-9 mmHg at 2, 3, 4, 5 and 6-10 minutes, respectively. Lactate was 0.9 mmol L^-1 at baseline, progressively increasing to 1.7-2.4 mmol L^-1 at 7-10 minutes. Packed cell volume increased after 7 minutes of apnea. There were no other major changes.

CONCLUSIONS AND CLINICAL RELEVANCE

Apnea immediately exacerbated hypoxemia and hypercapnia and rapidly caused hemodynamic instability. Apnea in hypoxemic anesthetized horses is associated with a serious risk for progress to cardiovascular collapse.