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INTRODUCTION TO ANESTHESIA & PRE-ANESTHETIC AGENTS. CHAPTERS 1 & 3. TERMINOLOGY OF ANESTHESIA. Anesthesia may be defined as “loss of sensation”, but this only describes one of its effects.

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terminology of anesthesia
TERMINOLOGY OF ANESTHESIA
  • Anesthesia may be defined as “loss of sensation”, but this only describes one of its effects.
    • It is used daily in most veterinary practices to provide sedation, tranquilization, immobility, muscle relaxation, unconsciousness, and pain control for a diverse range of indications including surgery, dentistry, grooming, diagnostic imaging, wound care, and capture/transport of wild animals
terminology of anesthesia1
TERMINOLOGY OF ANESTHESIA
  • Sedation refers to drug-induced CNS depression and drowsiness that vary in intensity from light to deep.
    • Patient can be aroused by noxious stimuli
  • Tranquilizaionis a drug-induced state of calm in which the patient is reluctant to move and is aware of but unconcerned about its surroundings.
    • Often used interchangeable with sedation
terminology of anesthesia2
TERMINOLOGY OF ANESTHESIA
  • Hypnosis is a sleeplike state from which the patient can be aroused with sufficient stimulation.
  • Narcosis refers to a drug-induced sleep from which the patient is not easily aroused and that is most often associated with the administration of narcotics.
terminology of anesthesia3
TERMINOLOGY OF ANESTHESIA
  • General anesthesia may be defined as a reversible state of unconsciousness, immobility, muscle relaxation, and loss of sensation throughout the entire body produced by administration of one or more anesthetic agents.
    • Surgical anesthesia is a specific stage of general anesthesia in which there is sufficient degree of analgesia(loss of sensitivity to pain) and muscle relaxation to allow surgery to be performed without patient pain or movement.
slide6

Fully conscious

Awake

Light sedation

Moderate sedation

Sedation

Deep sedation

Border between

Consciousness and

unconsciousness

Hypnosis

Narcosis

Light surgical anesthesia

Unconscious

Moderate surgical anesthesia

General

anesthesia

Deep surgical anesthesia

Anesthetic overdose

terminology of anesthesia4
TERMINOLOGY OF ANESTHESIA
  • Local anesthesia refers to loss of sensation in a small area of the body produced by administration of a local anesthetic agent in proximity to the area of interest.
  • Topical anesthesia is the loss of sensation of a localized area produced by administration of a local anesthetic directly to a body surface or to a wound.
  • Regional anesthesia refers to a loss of sensation in a limited area (larger area than with local anesthetics)of the body produced by administration of local anesthetic agent in proximity to sensory nerves.
terminology of anesthesia5
TERMINOLOGY OF ANESTHESIA
  • Balanced anesthesia refers to the practice of administering multiple drugs concurrently in smaller quantities than would be required if each were given alone.
    • Maximizes benefits of each drug
    • Minimizes adverse effects
    • Allows anesthetist to produce CNS depression, immobilization, and pain relief that is appropriate for the patient and the procedure.
pre anesthetic agents adjuncts
PRE-ANESTHETIC AGENTS & ADJUNCTS
  • ANESTHETIC AGENT: any drug used to induce a loss of sensation with or without unconsciousness.
  • ADJUNCTS: a drug that is not a true anesthetic but that is used during anesthesia to produce other desired effects such as sedation, muscle relaxation, analgesia, reversal, neuromuscular blockade, or parasympathetic blockade
    • Ex: muscle relaxants, neuromuscular blockers, reversal agents
pre anesthetic agents adjuncts1
PRE-ANESTHETIC AGENTS & ADJUNCTS
  • CHOOSING THE APPROPRIATE AGENTS
    • AVAILABILITY: most clinics will not have the option of choosing from every drug on the market.
    • FAMILIARITY: drugs are often chosen based on the veterinarian’s familiarity
    • PROCEDURE: drugs that are appropriate for one procedure may not be appropriate for another
      • Some drugs are short-acting and would not be appropriate for long surgeries
      • Some drugs may be appropriate for a spay but not a c-section
pre anesthetic agents
PRE-ANESTHETIC AGENTS
    • COST: It is ok to use a cheaper anesthetic as long as it is just as safe as the more expensive one.
    • TIME TO ONSET OF ACTION: in emergency situations, fast-acting drugs may be necessary
  • The anesthetic protocol, dose, and route are chosen by the veterinarian
  • Many clinics have a routine protocol, but is important to consider all aspects of the patient’s minimum database
pre anesthetic agents1
PRE-ANESTHETIC AGENTS
  • Drugs that are administered to an animal prior to general anesthesia
    • May be a single drug or combination of drugs
      • Do not mix two or more drugs unless you have reliable evidence that it is safe to do so.
  • REASONS TO ADMINISTER PRE-ANESTHETIC AGENTS
    • To calm or sedate an excited or fractious animal
pre anesthetic agents2
PRE-ANESTHETIC AGENTS
  • REASONS TO ADMINISTER PRE-ANESTHETIC AGENTS
    • To counteract the effects of other injectable or inhalant anesthetics
      • Ex: some anesthetic agents cause hypersalivation, we can use atropine or glycopyrrolate to counteract this effect.
    • To reduce the amount of general anesthetic agents required
      • If the patient is already sedated, it takes less drug to bring them into the unconscious state. This is a safer practice than using large amounts of drugs
      • Using smaller amount of both pre-anesthetics and anesthetic agents in combination is known as balanced anesthesia.
pre anesthetic agents3
PRE-ANESTHETIC AGENTS
  • REASONS TO GIVE PRE-ANESTHETIC AGENTS
    • To reduce pain & discomfort: some pre-anesthetic agents last long enough to be effective post-operatively
classes of preanesthetic agents
CLASSES OF PREANESTHETIC AGENTS
  • ANTICHOLINERGICS
  • TRANQUILIZERS and SEDATIVES
    • Phenothiazines
    • Benzodiazepines
    • Alpha-2 agonists
  • OPIODS
    • Agonists
    • Partial agonists
    • Agonist-antagonists
    • antagonists
anticholinergics
ANTICHOLINERGICS

aka parasympatholytics

or sympathomimetics

anesthetic surgical techniques may stimulate the vagus nerve
ANESTHETIC & SURGICAL TECHNIQUES MAY STIMULATE THE VAGUS NERVE
    • The vagus nerve provides parasympathetic innervation to numerous target organ such as:
      • Heart
      • Lungs
      • GI tract (viscerovagal reflex)
      • Secretory glands
      • Iris(oculovagal reflex)
  • When the vagus nerve is stimulated by endotracheal intubation, GI traction, or manipulation of the eye, what effect does it have on the organs above?
anticholinergics1
ANTICHOLINERGICS
  • Acetylcholine is the primary neurotransmitter in the PNS responsible for parasympathetic effects (cholinergic effects)

Ach

Ach

anticholinergics2
ANTICHOLINERGICS

These drugs are given to counteract the effects caused by vagal stimulation

EXAMPLES: Atropine, Glycopyrrolate

anticholinergics3
ANTICHOLINERGICS

Ach

Ach

ANTICHOLINERGICS ONLY AFFECT MUSCARINIC RECEPTORS

ON THE TARGET ORGANS

atropine vs glycopyrrolate a comparison
ATROPINE vs. GLYCOPYRROLATE: A COMPARISON
  • Both drugs can be given SQ or IM (preanesthetic purposes) or IV (emergency treatment of bradycardia/cardiac arrest)
    • Atropine is generally preferred for emergencies due to the quicker onset of action
  • Onset of Action/Duration of Action
    • Atropine IM: 5min, peak @ 10-20min, duration 60-90min
    • Atropine IV: 1 min, peak @ 3-4 min, duration several minutes
    • Glycopyrrolate IM: similar onset time to atropine, peak @ 30-45min, duration 2-3 hrs
atropine vs glycopyrrolate a comparison1
ATROPINE vs GLYCOPYRROLATE: A COMPARISON
  • Glycopyrrolate causes less tachycardia
  • Glycopyrrolate is better at decreasing salivation
  • TOXICITY
    • With overdoses drowsiness, excitement, dry mouth, ataxia, muscle tremors, dilated pupils, hyperthermia, and tachycardia may be seen
    • REVERSED with PHYSOSTIGMINE
      • Reversal is uncommon
  • ANTICHOLINERGICS ARE NOT CONTROLLED
tranquilizers and sedatives
TRANQUILIZERS and SEDATIVES

PHENOTHIAZINES

BENZODIAZEPINES

ALPHA-2 AGONISTS

general info on tranquilizers sedatives
GENERAL INFO ON TRANQUILIZERS/SEDATIVES
  • Tranquilizers reduce anxiety, but may not decrease awareness
  • Sedatives reduce mental activity and awareness and induce sleepiness

These terms are often used interchangeably

  • Patients that have received a tranquilizer/sedative may still be easily aroused and could potentially get aggressive or injure themselves

http://www.youtube.com/watch?v=AkaGWwTHD5g

phenothiazines

PHENOTHIAZINES

ACEPROMAZINE

CHLORPROMAZINE

general info on phenothiazines
GENERAL INFO on PHENOTHIAZINES
  • These drugs have no analgesic effects
  • These drugs are not controlled
  • These drugs do not have a reversal agent
  • Examples: Acepromazine, Chlorpromazine
what are the effects that phenothiazines have on the various body systems
WHAT ARE THE EFFECTS THAT PHENOTHIAZINES HAVE ON THE VARIOUS BODY SYSTEMS?

EFFECTS:

ADVERSE EFFECTS:

EFFECTS:

ADVERSE EFFECTS:

what are the effects that phenothiazines have on the various body systems1
WHAT ARE THE EFFECTS THAT PHENOTHIAZINES HAVE ON THE VARIOUS BODY SYSTEMS?

EFFECTS:

ADVERSE EFFECTS:

EFFECTS:

ADVERSE EFFECTS:

other effects adverse effects of phenothiazines
OTHER EFFECTS & ADVERSE EFFECTS of PHENOTHIAZINES:
  • ANTIHISTAMINE EFFECT
  • PENILE PROLAPSE
  • DECREASED PCV
  • Onset of action/duration of action
    • 15min after IM injection, peak@ 30-60 min
    • Duration: 4-8 hrs( could be up to 48hrs)
things to consider with phenothiazines
THINGS TO CONSIDER WITH PHENOTHIAZINES
  • Sedative effects can be overridden if patient is stimulated to a sufficient degree
  • Use a max of 3mg in dogs and 1mg in cats
  • Boxers and giant breed dogs by have increased sensitivity
  • Terriers and cats are more resistant to its effects
  • Chlorpromazine is used in veterinary medicine as an antiemetic, but not as an anesthetic adjunct.
benzodiazepines

BENZODIAZEPINES

DIAZEPAM

MIDAZOLAM

ZOLAZEPAM

general info on benzodiazepines
GENERAL INFO ON BENZODIAZEPINES
  • Benzodiazepines depress the CNS by increasing activity of endogenous gamma-aminobutyric acid (GABA), an inhibitory neurotransmitter in the brain.
  • These drugs are controlled
  • These drugs can be reversed
    • Flumazenil is the benzodiazepine antagonist. It is rarely used due to the very low incidence of adverse effects and the high cost.
  • These drugs provide no analgesia
  • These drugs have unreliable sedative effects & could induce dysphoria, excitement, or ataxia in young, healthy animals, esp. when given alone
    • EXAMPLES: DIAZEPAM, MIDAZOLAM, ZOLAZEPAM
whateffects do benzodiazepines have on the various systems of the body
WHATEFFECTS DO BENZODIAZEPINES HAVE ON THE VARIOUS SYSTEMS OF THE BODY?

EFFECTS:

EFFECTS:

ADVERSE EFFECTS:

things to consider about benzodiazepines
THINGS TO CONSIDER ABOUT BENZODIAZEPINES
  • Diazepam is not water-soluble and cannot be mixed with water-soluble agents except ketamine
    • Midazolam and zolazepam are water-soluble and can be mixed with other agents
  • Diazepam is is painful and poorly absorbed when administered intramuscularly
    • Midazolamis more readily absorbed via IM and SQ routes
  • Zolazepam is available only mixed with tiletamine to produce the combination product Telazol.
  • Diazepam is very soluble in plastic and over time is absorbed by syringes, IV bags, and IV tubing
things to consider about benzodiazepines1
THINGS TO CONSIDER ABOUT BENZODIAZEPINES
  • Diazepam and midazolam are light-sensitive
  • Onset of action/duration of action
    • Less than or equal to 15 min after IM injection
    • Duration: 1-4 hours
alpha 2 agonists

ALPHA-2 AGONISTS

XYLAZINE

DEXMEDETOMIDINE

general info on alpha 2 agonists
GENERAL INFO ON ALPHA-2 AGONISTS
  • These drugs are not controlled
  • These drugs can be reversed
  • These drugs do provide analgesic effects
  • These drugs act on alpha-2 adrenergic receptors in the CNS and PNS causing a decrease in the neurotransmitter norepinephrine
what effects do alpha 2 agonists have on the various body systems
WHAT EFFECTS DO ALPHA-2 AGONISTS HAVE ON THE VARIOUS BODY SYSTEMS?

EFFECTS:

ADVERSE EFFECTS:

EFFECTS:

ADVERSE EFFECTS:

what effects do alpha 2 agonists have on the various body systems1
WHAT EFFECTS DO ALPHA-2 AGONISTS HAVE ON THE VARIOUS BODY SYSTEMS?

EFFECTS:

ADVERSE EFFECTS:

EFFECTS:

ADVERSE EFFECTS:

other effects of alpha 2 agonists
OTHER EFFECTS OF ALPHA-2 AGONISTS
  • Hyperglycemia: alpha-2 agonists reduce the secretion of insulin by the pancreas
  • Hypothermia: alpha-2 agonists decrease thermoregulation and shivering
  • Premature parturition
  • Can be absorbed through the skin and abrasions – as little as 0.1ml of dexmedetomidine can cause hypotension and sedation in humans.
things to consider about alpha 2 agonists
THINGS TO CONSIDER ABOUT ALPHA-2 AGONISTS
  • Xylazine is largely reserved for use in large animals
    • Cattle are sensitive and only require 1/10 of the dose used in horses
  • Dexmedetomidine is largely used in small animals and is more potent than xylazine
  • Both drugs are commonly mixed with other drugs such as ketamine, and an opioidsuch as butorphanol or morphine
    • Animals can undergo minor and major surgical procedures with these combinations
things to consider about alpha 2 agonists1
THINGS TO CONSIDER ABOUT ALPHA-2 AGONISTS
  • These drugs can be reversed with Yohimbine (reverses xylazine) and Atipamezole (reverses dexmedetomidine)
    • Atipamezole is sold in combination with dexmedetomidine and is given in a 1:1 ratio
  • It is not recommended to treat bradycardia with anticholinergics, but rather the appropriate reversal agent
    • Reversal takes only 5-10min
opioids

OPIOIDS

AGONISTS

PARTIAL AGONISTS

AGONIST-ANTAGONISTS

ANTAGONISTS

general info on opioids
GENERAL INFO ON OPIOIDS
  • MODE OF ACTION
    • 3 Primary receptor in the brain and spinal cord
      • Mu, kappa, delta
  • SEDATION
    • ONSET OF ACTION:15min after IM administration
    • DURATION: 1-3 hrs for most (buprenorphine 6-8 hrs)
  • ANALGESIA
    • *excellent somatic and visceral analgesia
what effects do opioids have on the various body systems
WHAT EFFECTS DO OPIOIDS HAVE ON THE VARIOUS BODY SYSTEMS?

EFFECTS:

ADVERSE EFFECTS:

EFFECTS:

ADVERSE EFFECTS:

what effect do opioids have on the various body systems
WHAT EFFECT DO OPIOIDS HAVE ON THE VARIOUS BODY SYSTEMS?

EFFECTS:

ADVERSE EFFECTS:

EFFECTS:

ADVERSE EFFECTS:

other effects of opioids
OTHEREFFECTS OF OPIOIDS
  • Allergic reactions: morphine for example may cause facial swelling and hypotension after rapid Iv administration
  • Changes in body temperature: there is a resetting of the thermoregulatory center in the brain resulting in the dog panting and possibly lowering the body temperature
  • Cats may have an elevated body temperature for unknown reasons.
  • Miosis in dogs; mydriasis in cats
general info on opioids1
GENERAL INFO on OPIOIDS
  • These are controlled substances with human abuse potential
  • Opioids used in combination with a tranquilizer achieve a state of profound sedation and analgesia termed neuroleptanalgesia
  • These drugs can be reversed with the opioidantagonistNALOXONE (works within 2 min IV and 5 min IM)
    • Agonist-antagonists such as butorphanol can also be used to reverse the effects of pure agonists
  • These will be discussed further and in more detail in week 5-6