LATG Chapters 14

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LATGChapters 14 15PharmacologyAnesthesia
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Pharmacology

• The science that deals with origin, nature,
  chemistry, effects, and uses of drugs
• includes pharmacokinetics, pharmacodynamics,
  pharmacotherapeutics, and toxicology
• drugs are good, but may be only one factor

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Modes of Drug Action

• Stimulation increases the activity of cells
  (doxapram)
• Depression decrease cellular activity (atropine)
• Irritation leads to stimulation of activity
  (fleet enemas)
• Replacement synthetic substitutes (insulin or
  synthroid)
• Chemotherapy kill malignant tumor cells (Taxol
  or Doxorubicin)

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Drug Classification

• Classification systems primary effect site of
  action
• Primary effect unknown cause, but drug may
  relieve clinical signs
• Site of action organ specific drugs

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Routes of Administration

• Enteral drugs are delivered directly into GI
  tract slower absorption wider safety margin
• Oral Rectal
• Oral tablets, capsules, powders, solutions,
  caplets, suspensions
• powders, solutions, or suspensions mix with food
  or require administration via stomach tube
• Rectal suppositories or enemas

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Routes of Administration

• Parenteral without or around (par)
• the intestines (enteral)
• IV, SC, ID, IM, IP, IC
• quickest route to get drug into animal to site
  of action
• other routes Intra-articular Subarachnoid or
  Intrathecal, subconjunctival
• drugs given should be sterile, nonirritating, and
  pyrogen-free

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Routes of Administration

• Inhalation directly into respiratory tract
• gas, vapor, fine mist or powder
• particles or droplets must be less than 5um
• most commonly used for anesthetic gases (i.e.
  isoflurane)
• advantages rapid absorption and elimination
• disadvantages intubation, mask, or inhalation
  chamber

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Routes of Administration

• Topical application to skin or external
  membranes
• lotions, ointments, pastes, and suspensions
• slowest rate of absorption
• advantages high doses to local area without
  systemic toxicity
• disadvantages fur, dirt, bedding, licking

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Dosage Forms

• Enteral forms solutions, suspensions, capsules,
  or tablets
• Solutions water based, tinctures, spirits, fluid
  extractions
• Suspensions insoluble drugs
• Capsules soluble in stomach or intestine
  (time-release)
• Tablets solid preparations (enteric coating)

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Dosage Forms

• Parenteral forms mixed or dissolved in a
  sterile, pyrogen-free medium
• IV, IA, IC drugs dissolved in water, isotonic
  saline, or saline-dextrose
• Depot effect drug dissolve slowly gives a
  constant drug level

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Therapeutic Use of Drugs

• Tolerance decrease in response to normal dose
  (e.g., NHP to ketamine)
• Sensitization increase in response (e.g.,
  allergic reactions)
• Synergistic two or more drug which give an
  enhanced response (e.g., antibiotics)
• Potentiation increased action by one drug
  produced by another drug with nonrelated action

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Therapeutic Use of Drugs

• All drugs have a toxic effect if given in excess
• Therapeutic Index or Margin of Safety
• TI Toxic dose/Effective dose

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Distribution and Elimination

• Distribution of drugs within the body varies
  considerably
• Most drugs are inactivated by normal metabolic
  processes
• Kidneys primary route of excretion
• Other routes bile, respiratory
• Metabolism mostly occurs in the liver

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Controlled Drugs

• Schedule III-V less potential for abuse
  (ketamine, butorphanol)
• Requires federal and state licenses
• Detailed records showing usage
• Facilities which use controlled drugs may be
  inspected by DEA
• Must be stored behind at least two locked doors

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Controlled Drugs

• Potential for being abused or addictive
• Comprehensive Drug Abuse and Control Act lists
  control drugs and 5 schedules
• Schedule I high potential for abuse no medical
  treatment, no safety (LSD, heroin)
• Schedule II high potential for abuse, but have
  medical uses (codeine, opium derivatives,
  pentobarbital)

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Dogs

• Parvovirus
• acute disease of young dogs
• bloody diarrhea and severe panleukopenia
• Otitis Externa
• bacteria, yeast, ear mites (Otodectes cynotis)
• factors dirt, trauma, hair, foreign bodies
• excess head shaking and odor
• Heartworms
• Dirofilaria immitis spread by mosquitos
• adults live in pulmonary artery, right artium,
  and right ventricle

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ANESTHESIA
Review dosage calculations using ratios and cross
multiplication
Review the stages and planes of anesthesia Stage
1 - narcosis, sedation, analgesia Stage 2 -
uninhibited response, delirium, excitement Stage
3 - surgical stage Plane 1 - loss of pain
response Plane 2 - surgical plane Plane 3 -
beginning of respiratory paralysis/pupil
dilation Plane 4 - cyanosis, non-responsive
pupils Stage 4 - paralysis of brain respiratory
centers
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ANESTHESIA

• Monitoring General Anesthesia

Respiratory Pattern - rate, depth and character
of the respirations Shallow, thoracic pattern
lightly anesthetized Deep, abdominal pattern
deeply anesthetized Pattern should be regular
Monitored by observing flow valves, rebreathing
bag, observing chest movement, in-line flow
meter
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ANESTHESIA

• Monitoring General Anesthesia

Mucous membrane color - The gums, lips,
rectum/vulva remain pink if the animal is
receiving enough oxygen. They turn blue if there
is a lack of oxygen.
Capillary refill time - Measured by pressing on
the gum line until the color blanches and timing
its return to normal color when pressure is
released. Normal is 2 seconds or less. Longer
times indicate a perfusion problem from lowered
cardiac output, increased vascular resistance, or
hypovolemia.
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ANESTHESIA

• Monitoring General Anesthesia

Pulse evaluation - Done on the femoral or
mandibular artery or the heart itself. The
strength and character of the pulse vary with
anesthetic depth and blood pressure.
Blood pressure - Blood pressure can be measured
indirectly using a pressure cuff on the tail or
leg and an ultrasonic doppler flow detector. An
arterial catheter can be used for direct BP.
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ANESTHESIA

• Monitoring General Anesthesia

Body temperature - Anesthesia affects the brains
heat regulatory center, lowering the patients
temperature. Loss is minimized by using a
heating pad, warm fluids, and a heat lamp during
recovery. Cooler temperatures slow
the metabolism of the anesthetic.
Eyes - Presence or absence of reflexes or
nystagmus, and size of the pupil indicate the
level of anesthesia
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ANESTHESIA

• Monitoring General Anesthesia

Muscle tone - varies with type of anesthesia
used. Ketamine results in stiff, rigid muscles.
Most other anesthetics result in some degree of
relaxation which is easily observed in the
larger species using jaw tone.
Reflexes - most common is the pedal or withdrawal
reflex, anal reflex also used. Both disappear
as surgical plane reached. Laryngeal reflex
used to determine time to remove endotracheal
tube
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ANESTHESIA Preanesthetics

• Preanesthetics include tranquilizers, analgesics,
  and anticholinergics
• Tranquilizers - lower the animals apprehension
  and aid in restraint for anesthetic induction
• Analgesics - work with the tranquilizer to lower
  the amount of general anesthetic needed,
  increasing the safety margin. CAN MASK THE
  ANESTHETIC STAGES.
• Anticholinergics - reduce secretions and raise
  heart rate

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ANESTHESIA Preanesthetics

• Anticholinergics - Atropine blocks acetylcholine
  resulting in decreased secretions from salivary
  and respiratory glands blocks the vagal tone on
  the heart, increasing the heart rate
• Tranquilizers - Phenothiazines reduce anxiety and
  cause muscular relaxation. Note These agents
  cause peripheral vasodilation and hypotension.
• -Analgesics - Medetomidine, Xylazine provides
  some anesthesia as well as analgesia and
  sedation. Often used with ketamine.

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ANESTHESIAInjectable Anesthetics

• Pentobarbital - Not to be confused with
  Phenobarbital. Long acting anesthetic that can be
  given IV or IP. For IV administration, half the
  dose is given quickly then titrated to the
  desired effect. No reversal agent. Must be
  very deep for analgesia.
• Thiamylal, thiopental, methohexital - Ultrashort
  acting (about 15 minutes) agents commonly used
  for general gas anesthetic induction.

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ANESTHESIAInjectable Anesthetics

• Chloral hydrate - Used primarily as a
  sedative/hypnotic due to poor analgesic
  properties. Can cause profound depression of
  cardiovascular and respiratory systems.
• Alpha-Chloralose - Poor analgesia and slow onset.
  Used in physiological studies since there is
  little effect on the cardiovascular and
  respiratory systems. Primarily used as a sedative.

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ANESTHESIAInjectable Anesthetics

• Urethane (Ethyl Carbamate) - Long lasting
  anesthetic. Has been associated with increased
  tumor formation. Can cause intestinal irritation
  if given IP. Usually used for long, terminal
  experiments.
• Tricaine Methanesulfonate (MS-222) - A water
  soluble anesthetic frequently used for fishes and
  amphibians.
• Fentanyl/Droperidol (Innovar-Vet) - An opioid and
  tranquilizer. Used for minor painful procedures.

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ANESTHESIAInjectable Anesthetics

• Ketamine HCl - A dissociative anesthetic.
  Administration results in excessive muscular
  tone, very mild respiratory depression, mild
  cardiac stimulation, salivation, adequate somatic
  but poor visceral analgesia. May produce
  seizures in some animals. Often used with
  xylazine for muscle relaxation and additional
  analgesia.

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ANESTHESIAInhalant Anesthetics

• Delivery and elimination occurs via the lungs
  easy to adjust level of anesthesia being
  administered.
• Supplied as a liquid that slowly evaporates at
  room temperature.
• Carrier gases (oxygen /- nitrous oxide) enter
  vaporizer where anesthetic gas vapor is added.
• Unused anesthetic gas and exhaled CO2 must be
  removed.

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ANESTHESIAInhalant Anesthetics - Delivery Systems

• Chamber system - Clear plastic or glass container
  with cotton soaked in anesthetic placed in bottom
  and covered by mesh or perforated floor. Animal
  placed on floor and lid put on container.
  Anesthetic induction can be observed through the
  container wall. Once animal is removed,
  recovery begins.
• Open Drop system - Nose cone with anesthetic
  soaked cotton used to maintain animals induced
  above.
• Both systems must be used in a fume hood.

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ANESTHESIAInhalant Anesthetics - Delivery Systems

• Rebreathing systems allows recirculation of
  carrier and anesthetic gas and consist of a
  number of components

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ANESTHESIAInhalant Anesthetics - Delivery Systems

• Vaporizer
• - Precision vaporizers are the most accurate and
  most commonly used type today. It automatically
  compensates for changes in vapor pressure due to
  temperature.
• Copper kettle - older style that requires user to
  adjust for temperature variations
• Wick-type - Used only with methoxyflurane since
  delivery concentration determined by liquids
  vapor pressure

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ANESTHESIAInhalant Anesthetics - Delivery Systems

• Lime Canister - Soda lime (calcium hydroxide or
  barium hydroxide) used to absorb the carbon
  dioxide in the expired air. A chemical indicator
  changes color when the soda lime should be
  replaced.
• Compressed Oxygen - Supplied in tanks available
  in a variety of sizes, green color code, full
  tanks 2200 psi indicated on regulator pressure
  gauge, delivery controlled by flowmeter (measured
  in l/m).

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ANESTHESIAInhalant Anesthetics - Delivery Systems

• Tubing and rebreathing bag - Allow for the
  one-way system to function. Rebreathing bag
  expands/contracts with each breath, should have a
  capacity of about 6 times the patients tidal
  volume.
• Pressure relief (Pop-off) valve - Adjustable,
  used to fine-tune flow rate so that the
  rebreathing bag stays about 2/3 full.

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ANESTHESIAInhalant Anesthetics - Delivery Systems

• Scavenger systems - Used to remove the excess
  exhaled gases Waste Anesthetic Gas or WAG
• Most effective is direct exhaust to the outside
  via central vacuum
• Activated charcoal canisters used on portable
  setups
• Leakage of anesthetic around tubing connections,
  around endotracheal tube, and at machine
  connections can occur and frequent equipment
  inspections should be performed.

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ANESTHESIAInhalant Anesthetics - Delivery Systems

• Non-rebreathing systems - used for animals
  weighing 7kg or less. Their tidal volume is
  too small to use the rebreathing systems so they
  use equipment that provides linear flow through
  the animal and then out to the scavenging device.
  This set-up produces large amounts of WAG.

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ANESTHESIAInhalant Anesthetics

• Vapor pressure - the higher the vapor pressure of
  a liquid, the quicker it will evaporate at a
  given temperature. The reason halothane and
  isoflurane cant be used in the open drop system
  but methoxyflurane can is due to the differences
  in vapor pressure.
• Tissue solubility - the greater the solubility of
  the gas in tissue, the slower the induction and
  the longer the recovery. Less soluble
  anesthetics are more potent.

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ANESTHESIAInhalant Anesthetics

• Diethyl Ether - highly flammable and explosive
  and must be used in explosion proof hoods. High
  tissue solubility slow induction and recovery
• Chloroform - NOT TO BE USED IN ANIMAL
  FACILITIES. Can be highly toxic to mice, has low
  margin of safety, is a known carcinogen.

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ANESTHESIAInhalant Anesthetics

• Methoxyflurane - Low vapor pressure and high
  tissue solubility safe. Can use wick-type
  vaporizers. Provides some analgesia after
  anesthetic recovery
• Halothane - Common veterinary inhalant
  anesthetic. High vapor pressure and low tissue
  solubility - use only precision vaporizers. Has
  been associated with cardiac arrhythmias.
• Isoflurane - Similar to halothane but no cardiac
  problems.

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ANESTHESIAInhalant Anesthetics

• Nitrous Oxide - Like oxygen, nitrous exists in a
  gaseous state at room temperature and is supplied
  in (blue) tanks. Under pressure it becomes a
  liquid. Tank pressure remains even (800 psi)
  until there is no more liquid, then it decreases
  as the remaining gas is used.
• Nitrous is combined with oxygen and should make
  up 50-80 of the carrier gas combination to be
  effective. Low tissue solubility rapid onset
  and recovery.
• Discontinue nitrous several minutes before oxygen

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ANESTHESIANeuromuscular Blockers

• ALWAYS USED IN CONJUCTION WITH GENERAL ANESTHESIA
  AND APPROPRIATE MONITORING
• gallamine, pancuronium, succinylcholine
• These agents cause paralysis of the voluntary
  skeletal muscles and, at higher doses, the
  diaphragm. Usually used with a ventilator. They
  provide NO analgesia.
• Indications fractures, dislocations,
  laparotomies
• Use BP, HR, mucous membrane color and capillary
  refill time to monitor anesthetic depth

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Analgesics

• NSAIDs - act by inhibiting prostaglandin
  synthesis, good for inflammation but not good for
  pain. Oral delivery. -Aspirin and
  Acetaminophen have limited use.
  - flunixin, ketoprofen, and
  carprofen
• Opioids
• Morphine provides sedation and analgesia. May
  also cause vomiting and defecation, cardiac and
  respiratory depression. Can see
  tremors/convulsions in mice and cats.
• Meperidine, Oxymorphone, Pentazocine,
  Buprenorphine

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Postanesthesia and Emergency Care

• Drugs to keep on hand for emergencies
• Apomorphine - induces vomiting
• Atropine sulfate - increases heart rate
• Calcium gluconate - strengthens myocardium
  contractions
• Chlorpromazine - tranquilizer
• Dexamethasone - steroid for shock/anaphylaxis
• Doxapram - stimulates breathing

• Epinephrine HCl - for asystole
• Heparin - dissolves blood clots
• Lactated Ringers - increases blood volume
• Morphine HCl - analgesia
• Pentobarbital - anesthesia
• Pitocin - stimulates uterus
• Sodium bicarbonate - acidosis
• Normal saline - increases blood volume
• Isoproterenol - stimulates heart

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Postanesthesia and Emergency Care

• Evaluation of patients should include behavioral
  observations and a complete physical examination
• Emergencies can usually be prevented by careful
  attention to the patient before, during, and
  after the anesthetic administration
• Technicians should work with the veterinarians
  both to avoid problems from occurring and to
  learn from those that do occur to prevent them
  from happening again.