euthanasia

euthanasia

• ending the life of an individual animal in a way that minimizes or eliminates pain and distress

• the process whereby an animal is killed using recognized acceptable human techniques

• criteria for a painless death including rapidly occurring unconsciousness followed by cardiac and respiratory arrest

methods of euthanasia

→ M1 inhaled agents

• inhaled anesthetics

• carbon dioxide

→ M2 non inhaled agents

• barbiturates (pentobarbital)

→ M3 physical methods

• captive bolt, gunshot, cervical dislocation, decapitation, electrocution, etc.

methods of euthanasia by species and environment

→ S1 companion animals

→ S2 lab animals:

• rodent

• lab farm animals, dogs, cats, ferrets, NHPs

• lab rabbits

• lab fish, amphibians, and reptiles

factors associated with decision to euthanize animals

→ necessity: cost of housing animals past their experimental usefulness and need to make room for new animals; emergency depopulation following natural disaster

→ relief from suffering: caused by disease or side-effects of experimental procedure

→ necropsy: for harvesting of tissues for histopathology or histochemistry

modes of action

→ hypoxia (direct or indirect): lack of oxygen to the brain

→ direct depression of neurons for vital life functions (respiration & heartbeats)

→ physical damage to brain tissue

evaluation and choice of methods- factors to consider

• death should occur without signs of panic, pain, or distress

• minimum time of loss of consciousness

• reliable/reproducible

• number of animals to be euthanized

• safety of personnel involved

• minimum undesirable physiological psychological effects

• compatibility with the requirement & purpose of the study

• minimal emotional effects on the observer & operator

• minimal environmental impact thru contamination

• simple, inexpensive, relatively maintenance free and “idiot roff” mechanical equipment

• location remote & separate from animal rooms

• cost

adequate training and experience for personnel performing euthanasia

• recognition of normal behavior in species being euthanized

• recognition of how handling and restraint affects that behavior

• understanding of the mechanism by which the selected technique induces loss of consciousness and death

• adherence to euthanasia SOPs

location where euthanasia is performed

→ animals must not be euthanized in the animal holding room where other animals are present and whom will continued to be housed there

→ distress vocalizations, fearful behavior, and release of certain odors or pheromones by a frightened animal during euthanasia may cause anxiety and apprehension in other animals that are not being euthanized

confirmation of death

• lack of pulse/heartbeat

• lack of breathing

• lack of corneal reflex

• lack of response to firm toe pinch

• inability to hear respiratory sounds and heartbeat by use of a stethoscope

• graying of the mucous membranes

physical methods

→ cervical dislocation

→ decapitation

→ exsanguination

→ focused microwave beam irradiation

chemical methods

→ carbon dioxide asphyxiation

→ inhalant anesthetic overdose

→ injectable anesthetic overdose

→ injectable euthanasia agent

cervical dislocation

• acceptable for mice, and for rats <200g

• rapid loss of consciousness

• allows collection of body tissues and body fluids uncontaminated by chemicals

• thumb and index finger are place on either side of the neck at the base of the skull, or, alternatively, a rod or instrument is pressed at the base of the skull, the other hand grasps the base of the tail which is quickly pulled in caudal direction

• separates cervical vertebrae from the skull, ruptured spinal cord, and ruptures blood vessels supply oxygen to the brain

• personnel who will perform CD without prior anesthesia must be properly trained and proficient in carrying out this technique

decapitation

• allows collection of body tissues and body fluids uncontaminated by chemical

• use of disposable flexible plastic cones to restrain animals reduces distress from handling, minimizes the chance of injury to personnel, and improves positioning of the animal

• equipment used to perform decapitation must be maintained in good working order and serviced on a regular basis to ensure sharpness of blades

• personnel who will perform decapitation without prior anesthesia must be properly trained and proficient in carrying out this technique

• risk of injury to fingers of personnel

bilateral thoracotomy

• not to be used as the primary means of euthanasia

• used as a secondary mechanical means of ensuring death following use of inhalant euthanasia

• using scalpel or scissors, cut skin and muscles between ribs on both sides of chest to allow air to enter chest cavity, resulting in collapse of lungs and cessation of breathing

exsanguination

• a terminal procedure that MUST be performed in sully anesthetized animal, so that animal does not experience pain or distress

• generally done via a laparotomy or thoracotomy

• for collection of large blood samples for analysis, or for ensuring death of the animal

• using a syringe and needle, blood is collected from the heart or any of the following vessels: abdominal aorta, vena cava, or hepatic portal vein

• used a secondary mechanical means of ensuring death following use of inhalant euthanasia agents

focus-beam microwave

• allows collection of body tissues and body fluids uncontaminated by chemicals- no pain, minimal distress

• does NOT involve a standard home microwave

• special commercial instrument designed for rodent euthanasia

• loss of consciousness in <100 milliseconds, death within 1 sec; carcass may convulse for up to 1 minute

• fixes bain metabolites in vivo while maintaining the anatomic integrity of the brain

  • phosphorylated proteins

  • acetylcholine, serotonin, endorphins

  • prostaglandins, catecholamines

  • C-AMP, C-GMP, GABA, DOPA

injectable anesthetic overdose

• injectable barbiturates and barbiture combinations generally act quickly and smoothly to render rodents unconscious

• pentobarbital is the most commonly used barbiturate for lab rodents because of its long shelf life and rapidity of action

• administered intraperitoneally; dose ranges:

  • rats → 150-200 mg/kg IP

  • mice → 200-250 mg/kg IP

• can cause histopathologic changes affecting pathology interpretation- focal congestion of intestinal serosa, congestion in pulmonary veins, necrosis in subcapsular levels of the liver and pancreas, lung emphysema and edema, and hyperemic kidneys

• other injectable anesthetic agents are acceptable, if animal is fully anesthetized, and a physical method is used to confirm death

inhalant anesthetic overdose

• inhalant anesthetics, such as isoflurane or sevoflurane, induce aversive behavior (distress) in rodents when exposed to the gass

• requires specialized equipment

• time to death can be slow- animals may need to be exposed for prolonged time periods to ensure death

  • odor of isoflurane makes animals hold their breath, delaying onset of loss of consciousness

• to confirm death, a secondary physical method should be used

• pose an exposure risk to personnel

carbon dioxide (CO2) asphyxiation

→ CO2 has the potential to cause distress

• carbonic acid formation on respiratory and ocular membranes

• creation of “air hunger”/breathlessness

• stimulation of amygdala, associated with fear response

→ CO2 has the potential to cause pain

• carbonic acid formation on respiratory and ocular membranes

to minimize animal distress and pain during CO2 euthanasia, staff must be appropriately trained

→ compressed CO2 gas in cylinders must be used

• do not use dry ice, fire extinguishers, or chemical reactions as source of CO2

→ use home cage as chamber, to minimize stress and anxiety

→ DO NOT pre-fill chamber with CO2 before adding animals

→ DO NOT overcrowd chamber with animals

• no more than 5 mice in chamber

• rats: <500g 2 per chamber; >500g 1 per cage

→ DO NOT place new animals in chamber with carcasses of animals already euthanized

→ flow sufficient CO2 to replace 30-70% of the chamber volume per minute

→ observe for complete cessation of breathing; continue flow for additional 2 minutes (neonates my require 10 min exposure)

→ recommended to use a secondary physical method to confirm death

→ following CO2 asphyxiation, death in neonates is assured by decapitation using sharp scissors

reasons for humane euthanasia of animals prior to completion of experiment

• rapid weight loss (15-20% within a few days)

• extended period of weight loss progressing to an emaciated state

• extensive or spreading area of ulcerative alopecia

• rough haircoat, hunched posture, distended abdomen or lethargy if debilitating or prolonged

• diarrhea if debilitating or prolonged

• coughing, rales, wheezing, and nasal discharge

• profound anemia or icterus

• rapid growth of a neoplastic mass

• CNS signs such as head tilt, tremors, seizures, circling, paralysis or paresis

• frank continual bleeding from any orifice

• markedly discolored urine, polyuria, or anuria

• persistent self-induced trauma

• lesions interfering with eating or drinking

• clinical sighs of suspected infectious disease requiring necropsy for diagnosis