INTRODUCTION TO ANESTHESIA & PRE-

ANESTHETIC AGENTS

CHAPTERS 1 & 3

TERMINOLOGY OF 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

• __________________ refers to drug-induced CNS depression and drowsiness that vary in intensity from light to deep.• Patient can be aroused by noxious stimuli

• _______________________ 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

• ________________ is a sleeplike state from which the patient can be aroused with sufficient stimulation.

• _____________________ 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

• __________________________________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.• _______________________________ 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.

Awake

Light sedation

Moderate sedation

Deep sedation

Hypnosis

Narcosis

Light surgical anesthesia

Moderate surgical anesthesia

Deep surgical anesthesia

Anesthetic overdose

Sedation

Generalanesthesia

Fully conscious

Border between Consciousness and unconsciousness

Unconscious

TERMINOLOGY OF ANESTHESIA

__________________ 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.

_________________ 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.

_________________ 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

• ___________________ 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.• _________________: 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• ____________________: most clinics will not have the option of choosing

from every drug on the market.

• ____________________: drugs are often chosen based on the veterinarian’s familiarity

• ____________________: 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

• ___________: It is ok to use a cheaper anesthetic as long as it is just as safe as the more expensive one.• ______________________________: 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• _________________________________________

PRE-ANESTHETIC AGENTS

• REASONS TO ADMINISTER PRE-ANESTHETIC AGENTS• _______________________________________________

• Ex: some anesthetic agents cause hypersalivation, we can use atropine or glycopyrrolate to counteract this effect.

• ________________________________________________• 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• _______________________________: some pre-anesthetic agents last long

enough to be effective post-operatively

CLASSES OF PREANESTHETIC AGENTS

ANTICHOLINERGICS

TRANQUILIZERS and SEDATIVESPhenothiazinesBenzodiazepinesAlpha-2 agonists

OPIOIDSAgonistsPartial agonistsAgonist-antagonistsantagonists

ANTICHOLINERGICSaka parasympatholytics

or sympathomimetics

ANESTHETIC & SURGICAL TECHNIQUES MAY STIMULATE THE

VAGUS NERVE• The ______________ nerve provides parasympathetic innervation to

numerous target organ such as:• Heart• Lungs• GI tract (viscerovagal reflex)• Secretory glands• Iris(oculovagal reflex)

• The vagus nerve can stimulated by endotracheal intubation, GI traction, or manipulation of the eye

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

ANTICHOLINERGICS ONLY AFFECT _________________RECEPTORS ON THE TARGET ORGANS

Ach Ach

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)• ______________ 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• ______________ 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 _____________CONTROLLED

TRANQUILIZERS and SEDATIVESPHENOTHIAZINESBENZODIAZEPINESALPHA-2 AGONISTS

GENERAL INFO ON TRANQUILIZERS/SEDATIVES

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

PHENOTHIAZINESACEPROMAZINE

CHLORPROMAZINE

GENERAL INFO on PHENOTHIAZINES

• These drugs have no _____________ effects• These drugs are not controlled• These drugs do not have a ____________ 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 minDuration: 4-8 hrs( could be up to 48hrs)

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.

BENZODIAZEPINESDIAZEPAM

MIDAZOLAMZOLAZEPAM

GENERAL INFO ON BENZODIAZEPINES

Benzodiazepines depress the CNS by increasing activity of endogenous ____________________________, an inhibitory neurotransmitter in the brain.

These drugs are ________________These drugs can be reversed

______________________ 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 ______________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:

ADVERSE EFFECTS:

EFFECTS:

WHAT EFFECTS DO BENZODIAZEPINES HAVE ON THE VARIOUS SYSTEMS OF

THE BODY?

EFFECTS:

EFFECTS:

THINGS TO CONSIDER ABOUT BENZODIAZEPINES

• Diazepam is not __________-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 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 ____________.• 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

ALPHA-2 AGONISTSXYLAZINE

DEXMEDETOMIDINE

GENERAL INFO ON ALPHA-2 AGONISTS

These drugs ________controlledThese drugs ___________reversedThese drugs do provide _____________ 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:

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

• ___________________ is largely used in small animals and is _______ 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 ______________ (reverses dexmedetomidine)• Atipamezole is sold in combination with dexmedetomidine and is given in a

__________ ratio

• It is not recommended to treat bradycardia with anticholinergics, but rather the appropriate reversal agent• Reversal takes only 5-10min

OPIOIDSAGONISTS

PARTIAL AGONISTSAGONIST-ANTAGONISTS

ANTAGONISTS

GENERAL INFO ON OPIOIDS

MODE OF ACTION3 Primary receptor in the brain and spinal cord

Mu, kappa, delta

SEDATIONONSET OF ACTION:15min after IM administrationDURATION: 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:

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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 OPIOIDSThese are controlled substances with human abuse potential

Opioids used in combination with a tranquilizer achieve a state of profound sedation and analgesia termed ________________________

These drugs can be reversed with the opioid antagonist _________________ (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