Download 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.
 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 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
 Tranquilizaion is 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 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 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.
Fully conscious
Awake
Light sedation
Moderate sedation
Sedation
Deep sedation
Border between
Consciousness and
unconsciousness
Hypnosis
Narcosis
Light surgical anesthesia
Unconscious
Moderate surgical anesthesia
Deep surgical anesthesia
Anesthetic overdose
General
anesthesia
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 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
 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 &
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
 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 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 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 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
 ANTICHOLINERGICS
 TRANQUILIZERS and SEDATIVES
 Phenothiazines
 Benzodiazepines
 Alpha-2 agonists
 OPIODS
 Agonists
 Partial agonists
 Agonist-antagonists
 antagonists
aka parasympatholytics
or sympathomimetics
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?
ANTICHOLINERGICS
 Acetylcholine is the primary neurotransmitter in the
PNS responsible for parasympathetic effects
(cholinergic effects)
Ach
Ach
ANTICHOLINERGICS
These drugs are given to counteract the effects
caused by vagal stimulation
EXAMPLES: Atropine, Glycopyrrolate
ANTICHOLINERGICS
Ach
Ach
ANTICHOLINERGICS ONLY AFFECT MUSCARINIC RECEPTORS
ON THE TARGET ORGANS
WHAT EFFECT DO ANTICHOLINERGICS HAVE ON
THE VARIOUS BODY SYSTEMS?
EFFECTS:
ADVERSE EFFECTS:
WHAT EFFECT DO ANTICHOLINERGICS HAVE ON
THE VARIOUS BODY SYSTEMS?
EFFECTS:
ADVERSE EFFECTS:
WHAT EFFECT DO ANTICHOLINERGICS HAVE ON
THE VARIOUS BODY SYSTEMS?
EFFECTS:
ADVERSE EFFECTS:
WHAT EFFECT DO ANTICHOLINERGICS HAVE ON
THE VARIOUS BODY SYSTEMS?
EFFECTS:
ADVERSE EFFECTS:
WHAT EFFECT DO ANTICHOLINERGICS HAVE ON
THE VARIOUS BODY SYSTEMS?
WHAT EFFECT DO ANTICHOLINERGICS HAVE ON
THE VARIOUS BODY SYSTEMS?
WHAT EFFECT DO ANTICHOLINERGICS HAVE
ON THE VARIOUS BODY SYSTEMS?
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 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
PHENOTHIAZINES
BENZODIAZEPINES
ALPHA-2 AGONISTS
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=AkaGW
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ACEPROMAZINE
CHLORPROMAZINE
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?
EFFECTS:
ADVERSE EFFECTS:
EFFECTS:
ADVERSE EFFECTS:
WHAT ARE THE EFFECTS THAT PHENOTHIAZINES
HAVE ON THE VARIOUS BODY SYSTEMS?
EFFECTS:
ADVERSE EFFECTS:
EFFECTS:
ADVERSE EFFECTS:
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
 Sedative effects can be overridden if patient is stimulated
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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.
DIAZEPAM
MIDAZOLAM
ZOLAZEPAM
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?
EFFECTS:
EFFECTS:
ADVERSE EFFECTS:
WHAT EFFECTS DO BENZODIAZEPINES HAVE
ON THE VARIOUS SYSTEMS OF THE BODY?
EFFECTS:
EFFECTS:
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
 Midazolam is 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
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
XYLAZINE
DEXMEDETOMIDINE
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?
EFFECTS:
ADVERSE EFFECTS:
EFFECTS:
ADVERSE EFFECTS:
WHAT EFFECTS DO ALPHA-2 AGONISTS
HAVE ON THE VARIOUS BODY SYSTEMS?
EFFECTS:
ADVERSE EFFECTS:
EFFECTS:
ADVERSE EFFECTS:
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
 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 opioid such as butorphanol or
morphine
 Animals can undergo minor and major surgical
procedures with these combinations
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
AGONISTS
PARTIAL AGONISTS
AGONIST-ANTAGONISTS
ANTAGONISTS
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?
EFFECTS:
ADVERSE EFFECTS:
EFFECTS:
ADVERSE EFFECTS:
WHAT EFFECT DO OPIOIDS HAVE ON THE
VARIOUS BODY SYSTEMS?
EFFECTS:
ADVERSE EFFECTS:
EFFECTS:
ADVERSE EFFECTS:
OTHER EFFECTS 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 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 opioid antagonist
NALOXONE (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