VT 100 Lec. 4 Chemical Restraint (wk. 2)

Purposes

Advantages:

• Reduces anxiety, fear related aggression, stress and struggling

• Immobilization

• Analgesia (pain relief)

• Anesthesia (medically induced sleep)

Disadvantage:

• Most are CNS depressants

• Many are CV and/or respiratory depressants

• Hypothermia

• Injury during induction or recovery

Routes of Administration

• Oral

  • Spray

  • Pill/liquid

• Parenteral

  • S.Q. = Subcutaneous

  • I.M. = Intramuscular

  • I.V.  = Intravenous

  • Darts

Considerations

• Species

• Physical factors

   1.  Age

   2.  Sex

   3.  Physical condition

  4.  Emotional status

  5.  Environment

Sedatives: Tranquilizers

• Tranquilizers – decreased anxiety and struggling but have normal consciousness

• Ace Promazine (phenothiazine) “Ace”

  •     Depresses CNS

  •     Anti-emetic

  •     Potent – long lasting

Sedatives: “Pre-visit pharmaceutical” (PVP)

• Trazodone

  • Antidepressant (SARI class)

  • Reduces anxiety = “anxiolytic”

  • Use in caution with patients that have kidney or liver disease

• Gabapentin

  • Used to treat seizures and nerve pain

  • Mechanism of action is not fully understood

  • Inhibits excitatory neurotransmitters in CNS

  • Often used as sole PVP in cats

  • Commonly used in combination with trazodone in dogs

Sedative: Agonist

• Substance that binds to a receptor and activates it

Sedative: Antagonist

Substance that binds to a receptor and inhibits activation

Sedative: Opioid Receptors

• Proteins found on the surface of cells in the brain, spinal cord, and other organs

  • Mu (µ) receptor = abundant, analgesia/euphoria

  • Kappa (ĸ) receptor = regulate sedation, GI function

  • Delta (δ) receptor = analgesia, reward/addiction

Sedatives: Butorphanol

• Opioid analgesic/sedative

• Much stronger sedative

• Partial mu (µ) receptor antagonist

  • Minimizes respiratory depression

• Kappa (ĸ) receptor agonist

  • Causes more sedation more than analgesia

Anxiolytics (anti-anxiety): Benzodiazepines

• Anti-convulsants

• Muscle relaxants

• Increases GABA in CNS

• Examples:

  • Diazepam

  • Midazolam

  • Alprazolam

Anxiolytics: Diazepam

• Administered PO or IV

• Recommend not IM

• “Lipophilic”

• Dissolves readily in lipids

• Slower onset of action

• Longer duration

 

Anxiolytics: Midazolam

• Administered PO, IV, IN or IM

• More “hydrophilic” than diazepam

• Rapid onset of action

• Shorter duration

Pharmacokinetics: absorption, distribution, metabolism, excretion

• Lipophilic Drugs:

  • Dissolves in lipid/fat

  • Fair absorption

  • Uneven distribution in fat/cells

  • Typically longer half-life

• Hydrophilic Drugs:

  • Dissolves in water

  • Excellent absorption

  • Good distribution in bloodstream

  • Typically shorter half-life

Alpha-2 Adrenergic Agonist: Dexmedetomidine (Dexdomitor)

• Causes sedation and analgesia

• IM on aggressive dogs

• IV-sedation in 3-5 min;  IM -5 to 10 min

• Often mixed with opioid

• Reversible

  • Antisedan (also reverses analgesia)

Alpha-2 Adrenergic Agonist: Xylazine (Rompun)

• Sedative/analgesic

• CNS depressant

• Increased CV effect

• Can be given IV or IM

• Commonly used in equine/large animal for standing sedation (ie: dental, sheath cleaning)

Alpha-2 Adrenergic Agonist: Detomidine (Dormosedan)

• Sedative and analgesic

• Longer duration than other alpha-2 agonists

• Administered IV, IM or transmucosally (PO)

• Can cause bradycardia and hypovolemia

Dissociative Anesthetics: Ketamine

• Sedation -> General anesthetic

• NMDA antagonist

• Short duration of action

• Provides analgesia too

• Often used as induction drug in combination with a benzodiazepine/alpha-2 agonist

 

Dissociative Anesthetics: Telazol

• Equal parts zolazepam (benzodiazepine) and tiletamine (dissociative)

• Long duration of action

• Used often with pigs and companion animals

• Administered IV, IM, IN, PO

TIVA = Total Intravenous Anesthesia

• Using multi-modal approach to maintenance of general anesthesia with minimal cardiovascular depression

• Using agents that are not cumulative (have a relatively short half-life)

• Using agents that are reversible

PIVA = Partial Intravenous Anesthesia

• Using multi-modal approach to maintenance of general anesthesia by minimizing the required MAC (mean alveolar concentration) to improve cardiovascular CRI (constant rate infusion) often used to maintain lowest MAC

  • Lidocaine, ketamine, fentanyl, morphine

  • Often “MLK” or “FLK” – all three used together as CRI

General Anesthesia Definition

“a state of medically-induced, reversible unconsciousness that provides pain relief and muscle relaxation for surgical procedures, keeping patients unaware of the procedure and allowing for control of breathing and other vital functions”

 

General Anesthetics: Anesthetic Gases

• Isoflurane, Sevoflurane

  • Intubation necessary

  • Metabolized through lungs

  • Rapid adjustment of doseand effect

  • Causes vasodilation and hypotension

  • Try to minimize inhalant dose with multi-modal anesthesia

General Anesthetics: Barbiturates

• Pentobarbital

  • Used as primary euthanasia drug

  • Not safe as an anesthetic

  • Narrow margin of safety

  • No longer used

• Phenobarbital

  • Used primarily as treatment for epilepsy

General Anesthetics: Propofol (Rapinivet)

• Used for sedation, induction and/or anesthetic maintenance by repeated bolus injection or CRI

• IV administration only.

• Minimal CV effect.  

• Transient apnea

General Anesthetics: Alfaxalone (Alfaxan)

• Neuroactive steroid

  • Affects GABA receptor

• Rapid onset

• Short duration of action

• Minimal CV effects

Opioids

• Provide sedative, hypnotic and analgesic properties

  • Decrease respiration

  • Causes bradycardia

  • Impair thermoregulation

  • Hypersensitivity to noise

  • Can be given SQ, IV, IM, PO or transdermal

  • Varying duration of action

Types of Opioids

• Hydromorphone

• Fentanyl

• Butorphanol

• Buprenorphine

• Morphine

• Methadone

• Codeine

Opioids: mu (µ) agonist

• Pure mu (µ) agonist

  • Hydromorphone

  • Fentanyl

  • Morphine

  • Methadone

• Partial mu (µ) agonist

  • Buprenorphine

Pure mu (µ) agonist

• Provides excellent analgesia

• Can cause significant CV and respiratory depression

• Can cause significant nausea and vomiting

• Can cause excitation in cats

 

 

 

Partial mu (µ) agonist

• Still good analgesia

• “Ceiling effect”

• Less CV/respiratory depression

• Less nausea/vomiting

 

 

Buprenorphine

• Long half-life, provides analgesia for up to 24 hrs or longer

• New transdermal product Zorbium ideal for post-surgery analgesia for up to 4 days!

Immobilizing Agents

• Important in veterinary medicine to facilitate examination, treatment and relocating of wildlife and feral animals

• Requires careful drug selection, dosage calculation, and administration to account for species-specific anatomical and physiological differences

• Common drug classes

  • Dissociative anesthetics

    • Ketamine, tiletamine

  • Opioids

    • Cafentanil, etorphine

    • Reversible (naloxone)

  • Alpha-2 agonists

    • Xylazine, medetomidine

    • Reversible (atipamezole)
      

Immobilizing Techniques

• Dart Guns

  • These devices fire darts containing the anesthetic drugs over a distance (up to 60 yards)

• Pole Syringes

  • Used for closer distances or physically restrained animals, these devices allow for hand injection or delivery via pressurized syringes

• Wildlife immobilization poses unique challenges and risks, including:

  • Species variability: Unpredictable, influenced by its species, age, sex, and health status.

  • Capture myopathy: Muscle damage that can lead to death in captive wild animals.

  • Hyperthermia: Agitated animals and certain drug combinations.

  • Human safety: Potent drugs, dangerous animals

Capture Myopathy

• Muscle damage (rhabdomyolysis) is central to the pathogenesis of capture myopathy

• Myoglobin and creatine kinase (CK), are released from the injured muscle fibres into the blood stream

• Blood lactate concentration is elevated leading to a decrease in pH and acidosis

• Acute kidney injury (AKI) often occurs and is associated with myoglobinemia

Capture Myopathy continued

• Eventually, multiple organ failure and death follow around 1-2 days after the initiating event

• There is no treatment for capture myopathy. The most successful approach is adopting preventative practices

• The use of tranquilizers during and after capture has aided in reducing the occurrence of capture myopathy but remains anecdotal at best

• Most commonly reported in ungulates(hoofed mammals), such as deer, mountain goats, and pronghorn, and long-legged wading birds like cranes and geese