Test #1: Euthanasia

Euthanasia PROPER terms:

• euthanize

• humanely kill

Euthanasia IMPROPER terms:

• inaccurate and/or insensitive

• putting to sleep

• putting down

• green needle

• blue juice

• zapping

• sacrifice

Regulatory Mandates:

• Animal Welfare Act

• PHS Policy

AVMA Guidelines for the Euthanasia of Animals:

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:

• euthanizing agents/physical methods terminate life by three basic mechanisms

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

  • direct depression of neurons for vital life functions (respiration and heartbeats)

  • physical damage to brain tissue

Evaluation and Choice of Methods:

• Of critical importance:

  • for acceptance as a humane method, method must have initial depressive action on the central nervous system (CNS) to ensure immediate insensitivity to pain

Evaluation and Choicr of Methods: Factors to Consider

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

• adherence to euthanasia SOPs

Location Where Euthanasia is Performed:

• animals should not be euthanized in animal holding room where other animals are present and who will continue 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 stethoscope

• graying of mucous membranes

Physical Methods of Euthanasia: Cervical Dislocation

• acceptable for mice and rats

• rapid loss of consciousness

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

• thumb and index finger are placed on either side of neck at the base of the skull

  • rod or instrument is pressed at base of skull while other hand grasps base of tail which is quickly pulled in caudal direction

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

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

Physical Methods of Euthanasia: Decapitation

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

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

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

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

• risk of injurt to fingers of personnel

Physical Methods of Euthanasia: Bilateral Thoracotomy:

• NOT to be used as primary means of euthanasia

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

• 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

Physical Methods of Euthanasia: Exsanguination

• terminal procedure that MUST be performed in fully anesthetized animal so that animal does not experience pain/distress

• generally done via laparotomy or thoracotomy

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

• using syringe and needle, blood collected from heart

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

Physical Methods of Euthanasia: Focused- Beam Microwave

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

  • no pain, minimal distress

• does NOT involve standard home microwave

• special commercial instrument designed for rodent euthanasia

• loss of consciousness in <100 milliseconds

  • death within one second

• fixes brain metabolites in vivo while maintaining the anatomic integrity

Chemical Methods of Euthanasia: Injectable Anesthetic Overdose

• injectable barbiturates combination generally act quickly and smoothly render rodents unconscious

• pentobarbital is most common for lab rodents because of its long shelf life and rapidly of action

• administer intraperitoneally

• can cause histopathologic changes afffecting pathology interpretation

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

Inhalant Anesthetic Overdose Facts:

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

• 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, secondary physical method should be used (ex: cervical dislocation, bilateral thoracotomy)

• pose an exposure risk to personnel

Chemical Methods of Euthanasia: Carbon Dioxide (CO2) Asphyxiation:

• CO2 has potential to cause distress:

  • carbonic acid formation on respiratory and ocular membrane

  • 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

CO2 Asphyxiation: to minimize animal distress and pain during euthanasia, follow these protocols:

• compressed co2 must be used

  • DO NOT use dry ice, fire extinguishers or chemical rxns as source

• 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

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

• flow sufficient co2 to replace 30 to 70% of chamber

• observe for complete cessation of breathing

• recommended to use a secondary physical method to confirm death

• death in neonantes should be assured by decapiation using sharp scissors

Unacceptable Methods of Euthanasia:

• neuromuscular blocking agents

• carbon monoxide

• nitrogen or other inert gases

• cyanide gas

• morphine

• electrocution

• drowning

• IV air embolism

• volatile anesthetics administered IV

• exsanguination without anesthesia

• concussion