Pre-Anesthetic Drugs and Analgesia

Anesthetic Agent

any drug used to induce a loss sensation w/or w/out unconsciousness

adjunct

used to describe a drug that is not a true anesthetic but is used to produce other desired effects such as sedation, muscle relaxation, analgesia, reversal, neuromuscular blockade, or parasympathetic blockade

preanesthetic meds

drugs given before gen anesthesia

reversal agents

lessen or abolish the effects of other anesthetics(wake pts)

induction agents

used to induce gen anesthetics

maintenance agents

used to maintain gen anesthesia

pharmacokinetics

effect the body has on a drug

pharmacodynamics

effect drug has on a body

agonist

binds to and stimulates tissue receptors in the cns

antagonist

bind to and stimulates receptors(block agonist)

*reversal agent

analgesia

loss of sensitivity to pain(given before, during, and after anesthetic event)

pain control- analgesia

gen anesthetics provide a lack if awareness of pain while unconscious- so when they are under pain is no perceived consciously but comes back when conscious again - pain may not consciously but can cause changes leading to harder pain control which can compromise the pt

must be given before, during, and after

drug enforcement agency DEA

regulates purchasing, handling and disposal of controlled substances

detailed records

controlled substance act US

each drug assigned to 1 of 5 drug schedules according to its potential for abuse

controlled substances must be kept in a double-locked cabinet safe or other secure storage

usage mist be accurately recorded in a drug locked book

used must be recored

periodic checks of inventory required

Schedules of controlled substances

C-V to C-I

preanesthetic meds

agents most commonly admitted during anesthetic period: alone or part of balanced anesthesia

pre meds

anxiolytics

tranquilizers and sedatives- phenothiazines, benzodiazepines

anticholinergics

alpha2-adrenceptor agonists(alpha2-agonists)

opioids

a premed

a single or combo of drugs given to an animal prior to gen anesthesia

most animals under going gen anesthesia should get premeds

based on hx, pe, tests, and anesthetic risk

premeds should be given 15 to 20 mins before

i’m and sq most common

im faster onset

sc lasts longer

also given iv or orally

3 groups of premeds

anticholinergics(parasynpatholytics)

sedatives/tranqulizers

analgesics

purpose of giving premeds

decrease pt stress/anxiety of trip to the hospital

calm/sedate frightened/excited/fractious pt(safe and stress free handling)

pt is more relaxed(easier transition to anesthesia)

reduce peioperative nausea, vomiting, other complications

purpose of premeds 2

minimize adverse of effects on other given drugs at the same time

pain meds are given at right time-before pain starts

easier induction and recovery

muscle relaxation

easier catheter placement, minimize amount of induction agent/maintenance anesthesia and lower risk of gen anesthesia

balanced anesthesia benefits

maximize benefits of each drug

less adverse reactions

gives anesthetist ability to produce anesthesia at degree of cns depression, muscle relaxation, analgesia, and immobilization for the pt and procedure

premeds for weak, debilitated, geriatric, pediatric, or sick animals

w/o induction need higher dose of anesthesia leading to high risk of

hypotension or hypoventilation- pt may not recover

other uses of premeds- tranquilizers

calm pts for transports, pe, radiographic procedures wound treatment, prevent chewingg wounds/bandages

other uses of premeds-benzodiazepine

diazepam used IV (also rectal), to stop seizures, appetite stimulant

other uses of premeds-phenothiazines

antiemetic properties

other uses of premeds-opioids

effective cough suppressants

premeds can be contraindicated

weak/debilitated, geriatric, sick, unresponsive

pregnant

exacerbate existing illness/condition

quick procedure/outpt sx

anxiolytics-gabapentin

developed at human anticonvulsant

off-label as anxiolytic and analgesic in vet pts

also anticonvulsant in vet pt

analgesic adjust for neuropathic pain and hypersensitivity

temporary//mild adverse effects: drowsiness and incoordination(ataxia)

for fear/anxiety for vet visits

can take 2-3 hrs for effect- liquid for can have xylitol(toxic)

not federally controlled- no FDA approval for use in animals

anxiolytics-trazodone

human antidepressant

used to reduce fear, anxiety, and stress in dogs prior to visit(similar to gabapentin)

treat anxiety disorders/situational anxiety

non controlled and FDA approved in animals

adverse effects include sleepiness, lethargy, and ataxia

gi effects- vomitijg, diarrhea, decreased appetite

cam be given w/or w/out food

AAFP guidelines in cats

Sympathetic nervous syste- epinephrine and norepinephrine(neurotransmitter): fight to flight

increased hr

dilated pupils(mydriasis)

dilation of bronchi

decreased gut mobility

relaxation of urethral sphincter

parasympathetic nervous system

vagus nerve(10th cranial nerve)

parasympathetic- acetlychroline(main neurotransmitter)

decreased hr

constricted pupils

bronchi constriction

increased gut motility

contraction of urethral sphincter

vagus nerve

10th cranial nerve: vasovagal nerve travels from the brain to the distal large intestine

controls digestion/relaxation

activating the nerve activates rest and the digest system(parasympathetic nervous system) and deactivates the flight or fight response(sympathetic nervous system)

regulates hr, rr, blood pressure, digestion, and just about everything in between

plays a role in hearing, vision, and mental functioning

viscerovagal reflex

during sx vagal nerve may be stimulated by et intubation increased acetylcholine binding

traction on abdominal organs, manipulation of eye during ocular sx, some drugs and anesthesia

bradycardia, bronchoconstriction, excess tear/salvia production of respiratory excretions, increased go motility and miosis

brachycephalic are at higher risk for viscerovagal reflex

known for walking around with increased vagal tone

some vets recommended premeds w/anticholinergic-glycopyrrolate since it last longer in these breeds

anticholinergics- parasympatholytics

block passage if impulses through parasympathetic nerves

block acetylcholine

reduce bradycardia- increase hr

dry oral secretions- decrease salivary secretions

reduce gi activity- v or d

pupil dilation

blocks stimulation of vagus nerve- by et intubation and handling of vicara/eyes

non controlled- used less in vet med then in the past

contraindications of anticholinergics

increase incidence of cardiac arrhythmias and sinus tachycardia

constipation

thick mucus secretions(block airway-cat)

endoscopic procedure

bronchodilation(esp in cats-asthma)- cause thick mucous secretions

atropine sulfate

faster onset of action than glycopyrrolate(im 5 mins)

decrease excess salivary secretions

treat bradycardia: er drug

rapid elimination

given sq im or iv

contraindicated in fertile pts:crosses blood brain barrier(interferes with/ thermoregulation)

non controlled

glycopyrrolate

better at reducing salivary secretions

prevent bradycardia- less likely to cause cardiac arrthmias

minimal effects on heart

im sq or iv

minimally crosses blood brain barrier/placenta

non controlled

sedatives

reduce stress, fear, anxiety

causes reduced mental activity and sleepiness

may possess analgesic properties

tranquilizers

reduce anxiety but does not always decrease awareness/wakefulness

no analgesic properties

tranqulizers and sedatives

effects are ataxia and prolapse of nictitating membrane

terms used interchangeably

given to help calm pt and easy handling

gen risks for tranq and sedatives

do no leave pts unattended- risk of falling

relaxes pharynx tissues causing deadly respiratory distress in brachycephalic- respiratory stridor

sudden arousal or aggression when stimulated

phenothiazines- acepromazine

• Given IM:  15 minutes to take effect, may last 4-8 hours  (or SQ):  place in quiet location, free of stimulation

• Mild sedation

• Calming effect, reduced alertness, CNS sedation

• Antiemetic effect

• Antiarrhythmic effect

• Antihistamine effect:  prevents release of histamine (decreases allergic reaction)

• Blocks epinephrine:  peripheral vasodilation (↓BP)

• Inhibit temperature regulation

• Effects on personality (induce excitement)   QUIET

• NO ANALGESIC effect

• *Manufacturer recommended dose higher than actual dose  required for preanesthesia    (reduce dose to minimize adverse effects)

• Responses to acepromazine are species and breed specific

• Non-controlled drug

acepromazine

increased potency in: geriatric, neonates, debilitated pts, liver/cardiac dysfunction

decreases allergic response during allergy testing

chlorpromazine

benzodiazepines- diazepam, zolazepam(w/tiletamine), and midazolam

• Minor tranquilizer, Flumazenil (reversal agent)

• Rapid onset IM  < 15 minutes  Duration 1 to 4 hours

• Antianxiety and calming effect (minimal CNS depression), not drowsy

• NO ANALGESIC effect

• Anticonvulsant activity (IV or rectally)

• Skeletal muscle relaxation

• Minimal adverse effects on cardiovascular/respiratory systems

• Potentiation of general anesthesia:  enhances sedation and analgesia of other agents (including inhalant agents)

• Contraindicated in liver disease

• Unreliable sedative effects in dogs, cats and horses:  may cause dysphoria,         excitement, and ataxia

•    Soluble in plastic

• Controlled drugs

diazepam-valium

• Used in combination with other drugs to induce anesthesia (*ketamine)

• Give slowly IV:  pain, bradycardia, hypotension, apnea

• IM or SQ painful, irritating to tissues, poorly absorbed

• Not water-soluble:  ONLY mix in same syringe with ketamine

          (forms precipitate with other agents, i.e. butorphanol)

• Light sensitive

• Soluble in plastic, i.e. syringes

• Crosses the placenta, ↓CNS in neonates

• Hepatic failure in cats (oral)

• Other uses:  CATS  appetite stimulant (IV in hospital)

zolazepam

• Only available mixed with tiletamine

midazolam

• now the “benzo of choice”

• water soluble, can be mixed with other agents

• hypotension when given IV

• less irritating to tissues when given IM or SQ

• no sticking to plastic in syringes

• crosses the placenta

• light-sensitive

• Disadvantage:  some dogs/cats will become ‘hyper’ when given midazolam or a little agitated, “midaz crazies”!

• Do not give alone:  give with opioid or opioid + acepromazine

• Induction benzodiazepine of choice when given w/ketamine—”ket-midaz” induction

alpha 2-adrenoceptor agonists- zenalpha, atopamezole, dexmedetomidine, xylazine, detomidine, romifidine

• Cause a ↓ in neurotransmitter norepinephrine (sympathetic nervous system)

• Combination w/other tranquillizers or analgesics:  synergistic effects

• Potent sedatives, noncontrolled drugs

• Fast onset, reliable and potent effect, reversibility

• Quiet environment for 10-15 minutes after injection (agitation, aggression)

• Provide analgesia, muscle relaxation

• Onset of action IV 5-15 minutes, IM 15-30 minutes, duration of 1-2 hours

    complete recovery: 2-4 hours if not reversed

• Metabolized in liver, excreted kidneys:  use in healthy animals (normal liver/kidney function), GI:  vomiting

• Can be used as a premed or induction for minor procedure

• Bradycardia, cardiac arrhythmias

• Initial hypertension, then hypotension

• Respiratory depression and vasoconstriction (cyanotic mm)

• Careful monitoring of VITAL signs

• ↓ insulin secretion → hyperglycemia

alpha 2-adrenoceptor agonists contraindications

• Geriatric or debilitated animals

• Heart disease or respiratory disease

• Pregnant animals

• Liver or kidney disease

• Hypotensive or dehydrated animals

• Dogs predisposed to GDV (bloat)

• Hyperglycemia

xylazine

• Potent sedative effects

• Profound cardiovascular depression

• Large and small animals, IM or IV

• Analgesic effect

• Causes vomiting

• Can be used in combination with other agents

• Reverse with alpha-2-antagonist:

           Yohimbine:  cats, dogs, horses,

                                    exotics

              Tolazoline:  ruminanmts

• Non controlled drug

dezmedetomidine- dexdomitor

• Most commonly used alpha-2-agonist (2008)

• For use in dogs and cats

• Greater potency and fewer adverse effects than xylazine

• Provides sedation, muscle relaxation and analgesia

• IM in dogs and cats, IV use in dogs only

• Dose determined according to body surface area

• Can be used in combination with other agents:  butorphanol, buprenorphine, ketamine

• Quiet environment 10-15 minutes after injection

• Sileo® transmucosal canine gel for noise phobia

• Non controlled drug

atipmezole(antisedan)

• •Specific antagonist for dexmedetomidine: (packaged together):  dogs, cats, exotics

• •IM injection only      IV (emergency reversal)

• •10X more concentrated than dexmedetomidine:

         equal volume of drug administered to dogs; cats require little

         over half the dose

• •Reversal effects 5-10 minutes after injection

detomidine

• •Horses:  sedation, muscle relaxation, analgesia

• •Similar to xylazine (twice the duration of action)

• •Used with butorphanol:  standing sedation

• •Analgesia for colic

• •Transmucosal gel for horses

romifidine

• Similar to other alpha2 agonists, produces less ataxia

zenalpha(medetomidine and vatinoxan)

for use as a sedative and analgesic in DOGS only

intramuscular (IM) injection

NOT intended for use in CATS

facilitate clinical examinations, clinical procedures and minor surgical procedures

Zenalpha:  faster time to onset of sedation (5-15 minutes), faster recovery than dogs administered dexmedetomidine

short duration of sedation of approximately 45 minutes in most dogs:

    (average 38 minutes)

• reversal of Zenalpha: administration of IM atipamezole at the approved dose (reverse IM medetomidine):  reversal of sedation occurs within 5-10 minutes

• after administration, the dog should be allowed to rest quietly until evidence of sedation has occurred (5-15 minutes)

*As with all alpha2-adrenoceptor agonists, onset of sedation may be delayed or may

  be inadequate in some dogs

• per the American Society of Anesthesiologists ([ASA] classes I and II) only should be administered Zenalpha

• designed to maintain heart rate and blood pressure at nearly normal levels

• tachycardia may occur in some dogs after recovery from sedation

• adverse reactions reported: diarrhea, muscle tremors and colitis

• CONTRAINDICATIONS: Do not use in dogs with cardiac disease, respiratory disorders, shock, severe debilitation, hypoglycemia or are at risk of developing hypoglycemia, stress due to extreme heat, cold or fatigue

• Non-controlled

analgesics

The term analgesia applies to the relief of pain without the loss

of consciousness.

Pain relievers that can be used as premedications, induction agents,

intra- and post- operatively pain medications.

Animals with untreated pain:  may have increased fear and anxiety,

decreased cardiovascular function, decreased appetite, slower

wound healing and greater risk of infection, slower recovery in genera

any abnormal behavior can be a sign of pain

• Agitation or restlessness, vocalization (barking, crying, whimpering, groaning, growling)

• Quiet, depressed or inactive

• Frowning or squinting, laying back the ears

• Aggressive, resist handling

• Seek contact with caregiver

• Difficulty sleeping and lack of appetite

• •Stiff body movements, reluctance to move or hesitance to play or jump

• •CATS w/severe pain are commonly quiet, assume a hunched position in sternal recumbency, failure to groom themselves

• •Dogs may stare into space

• •Patient may lick, bite or scratch area of the pain sensation

• •Dilated pupils (mydriasis)

• •Increased heart rate, respiration, blood pressure

opioids

• Derived from opium (poppy)

• Opiates (naturally derived), synthetic compounds

• Analgesia, sedation, anesthetic induction when combined with other agents

• Controlled drugs: narcotics

• Administered IV, IM, SC, oral, rectal, transdermal, oral transmucosal (OTM),

     epidural, subarachnoid

• Reversal agents for most

• Agonist (stimulating agent) and antagonist (blocking agent) or BOTH

• Three major types of opioid receptors:  mu (μ), kappa (х), and delta (δ) – wide spectrum of effects-each opioid differs in action at each site

• Bind to and stimulate mu and kappa receptors-best drugs available for moderate to severe pain

• *Commonly mixed with a tranquilizer and/or anticholinergic and given during the

      pre anesthetic period

no true opioid contraindications

side effects are dose dependent- higher dose more complications

effects of opioids

• *Analgesic:  most effective agents in treatment of pain

• CNS depression in dogs or excitement in cats

• Bradycardia (vagus induced)

• Hypothermia in dogs-panting (brain receptors interpret false ↑BT)

• Hyperthermia in cats-unknown reason

• Changes in pupil size:  DOGS (myosis)   CATS (mydriasis)

• Increased responsiveness to noises

• Excessive salivation

• Hypotension

• Respiratory depression

• Increased peristaltic movement, V and D followed by constipation

• Decreased urine production and urine retention

contraindications opioids

• Patients on behavior medication

• Kidney and liver disease

• Respiratory disease

• FBO (vomiting)

• Severely dehydrated animals

opioids antagonists

• Naloxone hydrochloride IV or IM

• Butorphanol to reverse pure agonists

opioid treatment for moderate to severe pain

morphine, oxymophone, hydromorphone, methadone, fentanyl patches

morphine

First opioid used:  pure mu agonist; can be given IM, SQ, IV (slowly), intraarticular, epidural or spinal injection, may cause release of histamine, (↓ BP) if given too quickley

  - may cause GI stimulation and vomiting, salivation and defecation, excitement (CATS and HORSES), bradycardia, respiratory depression and panting

*Reduce incidence of vomiting by pretreating with Cerenia® 15-20 minutes before giving morphine

- duration:  2-4 hours if injected, 4-12 hours PO                                         

  - inexpensive