anesthetic pharmocology

anesthetic agent

drug that induces loss of sensation; with or without loss of consciousness

adjunct

drug used during anesthesia to produce other desired effects such as sedation, analgesia, reversal, or muscle relaxation

agonist

binds to stimulate target tissue

antagonist

binds to target tissue but does not stimulate it; usually reversal agents

partial agonist

binds to and partially stimulates the receptor

agonist-antagonist

binds to more than one receptor type; stimulates one receptor and blocks another

tranquilizers

reduce anxiety but do no reduce awareness/wakefulness

sedatives

reduce mental activity and cause sleepiness

phenothiazine

• drug: acepromazine

• adminstration route: IM or IV

• calms patient and decreases interest in surroundings and movement

• no reversal

• no analgesia

acepromazine side effects

• causes peripheral vasodilation: hypotension, hypothermia, increase HR

• reduce seizure threshold

• cause penile prolapse in large animals

• depress respiratory system

• splenic engorgement; lower PCV

• increased potency in neonates, geriatric, debilitated animals

TIVA

total intravenous anesthesia

PIVA

partial intravenous anesethesia

benzodiazepines

• diazepam, midazolam, zolazepam

• skeletal muscle relaxation

• anti anxiety

• rapid onset, short duration

• anticonvulsant

• appetite stimulant for cats and ruminants

• no analgesia

diazepam

• schedule IV drug

• slowly given IV

• can cause pain, apnea, hypotension, liver failure if given too fast

• not water soluble, no storage in plastic

• does not mix well with other drugs, other than ketamine

midazolam

• schedule IV

• give IM or SQ

• water soluble

zolazepam

powder that needs to be reconstituted

alpha 2 agonists

• sedation, analgesia, and muscle relaxation

• reversal = alpha 2 antagonists

• given IM or IV

• rapid onset, 1 to 2 hour duration

• usually for short procedures

• xylazine (rompun, anased)

• dexmedetomidine (dexdomitor)

• detomidine (dormosedan)

• romifidine (sedivet)

• detomidine/vatinoxan (zenalpha)

effects of alpha 2 agonists

• muscle relaxation and decreased muscle tone

• increase urination

• short analgesia, profound sedation

• bradycardia from vasoconstriction

• vomiting

• hypothermia

• avoid with geriatric, diabetic, pregnant, pediatric, ill

alpha 2 antogonists

• reverse alpha 2 agonists

• given IM or IV

• yohimbine and tolazoline reverse xylazine

• atipamezole reverse dexmedetomidine

• vatinoxan = peripheral alpha 2 antagonist; reverse only some

opioids

• analgesia and sedation

• given SQ, IM, IV, oral, rectal, transdermal, subarachnoid, epidural

• decreased resp and HR

• controlled substances

• last 2 to 4 hours

• nausea, vomiting, defication; followed by constipation, ileus, colic

neuroleptanalgesia

• profound state of sedation and analgesia

• administration of an opioid and a tranquilizer

• for procedures that require significant CNS depression

• may need to intubate and ventilate

• ace/torb, dex/buprenex

morphine

• pure mu agonist

• preanesthetic and analgesic

• somatic and visceral pain

• can cause excitement or dysphoria in cats/horses

• restlessness in dogs/horses

• causes: miosis (dogs), mydriasis (cats), hypothermia, hyperthermia (cats), bradycardia, panting, increased IOP, urinary retention

oxymorphone

• pure mu agonist

• greater analgesic potency and sedative effect

• fewer side effects and longer duration than morphine

• doesn’t release histamine

• does not decrease BP

hydromorphone

• pure opioid mu agonist

• similar to oxymorphone, but less potent

• premedication alone or with tranquilizer

• cause vomiting

• no histamine release

• less likely to induce excitement in cats

methadone

• schedule II

• opioid analgesic (synthetic opioid agonist)

• reduces amount of anesthetic to keep pet at surgical plane of anesthesia

fentanyl

• one of most potent analgesics known

• rapid onset IV (2 min)

• short duration IV (20 to 30 min)

• IV drip, transdermal patch, IM, SQ, epidural injection

• combo with midazolam or diazepam

fentanyl transdermal patch

• fentanyl enclosed in plastic

• attach to clipped skin; can stay for several days

• 20, 50, 75, or 100 mcg/hr

opioid transdermal patch

• longer duration of effect

• delay of action 4 to 12 hrs (cats)

• delay of action 12 to 24 hrs (dogs)

• apply 6 to 12 hours before start of surgery

• DO NOT use butorphanol or buprenorphine with fentanyl

• monitor for ataxia/sedation (dogs) and dysphoria/disorientation (cats)

• heat can increase amount fentanyl absorbed

buprenorphine

• patial mu agonist

• some analgesia; mild to moderate pain

• can partially reverse morphine and fentanyl

• ceiling effect

• may cause respiratory depression

• IV, IM, epidural, or oral (cats)

• longer duration

buprenorphine transdermal solution

• zorbium

• topic liquid on pets skin

• takes 30 min to absorb into pet

• onset = 1 to 2 hours after fully absorbed

• can release in system up to 4 days after application

• may make cats act “high” for 3 to 4 days

butorphanol

• preanesthetic, sedative, post-op visceral analgesic

• synthetic opioid

• agonist and antagonist

• can reverse effects morphine and fentanyl

• IV, IM, SC, oral

• schedule IV

• cough suppressant

opioid as epidural

• administer after induction anesthesia

• onset of action: 20 to 60 min

• duration of action: 6 to 24 hr

• reposition animal every 2 to 4 hours

• may form epidural hematomas and abscesses

tramadol

• synthetic opioid

• schedule IV

• postop alternative to opioid

• can be administered at home

• do not use with Norepinephrine/serotonin reuptake inhibitor

NSAID mechanism of action

• onset 30 to 60 min

• for somatic and visceral pain

• metabolized in liver, eliminated by kidneys/GI tract

• inactivated COX

COX

• cox 1: GI protect ant, modulate blood flow to kidneys

• cox 2: inducible by tissue damage; present in CNS, kidney, repro, eyes

NSAID effects

• analgesia and anti inflammatory

• does not depress CNS

• may cause GI issues, hemorrhage, renal toxicity, prolonged bleeding time, liver damage

robenacoxib

• onisor

• pill/injectable

• COX 2 selective

• 4 months and older, 2.5kg and bigger

• give 30 to 45 min before surgery

• may cause vomiting, diarrhea, increased liver enzymes

carprofen

• rimadyl

• COX 1 and 2 inhibition

• caplet, chewable, injectable

• not recommended for cats

• long term for arthritis

• may cause stomach ulcers, black tarry stool, liver/kidney issues

meloxicam

• metacam

• COX 2 selective

• injectable and liquid

• must be given with food

• may cause vomiting, diarrhea, loss of appetite

induction agents

• injectable anesthetic agents

• produce unconsciuosness

• no analgesia or muscle relaxation

• give IV slowly TO EFFECT

propofol

• schedule IV

• short acting: 5 to 10 min

• onset of action = 30 to 60 seconds

• recovery in 20 to 30 min

• muscle relaxation, antiemetic

• may cause nystagmus, hypotension, apnea

alfaxalone

• schedule IV

• IV or IM

• onset of action = 30 to 60 seconds

• duration = 5 to 10 min

• wide margin of safety

• less cardiovascular effects

entomidate

• hyponotic anesthetic agent

• ONLY IV

• longer recovery

ketamine and tiletamine

• dissociative

• onset of action 1 to 2 min IV / 10 min IM

• lasts 20 to 30 min

• analgesia to skin and limbs, amnesia, no response to external stimuli, increases muscle tone

dissociative effects

• sensitivity to light, sound, sensory stimuli

• exaggerated responses

• decreased heart contraction strength

• pain with IM injection

• increase salivation

anticholinergic

• blcok acetylcholine neurotransmitter

• IV, IM, SC, IT

• atropine: faster onset, shorter peak and duration

• glycopyrrolate: slow onset, longer peak and duration

• prevent and treat bradycardia, reduce secretions and GI motility, dydriasis, bronchodilation

• may cause cardiac arrhythmia, thickened secretions, colic (horses), bloat (ruminants)

guaifenesin

• glyceryl guaiacolate either (GGE)

• not analgesic or anesthetic

• use with ketamine

• for large animals at CRI

• muscle relaxation, facilitate intubation, increase ease of induction/recovery

• IV until ataxic

• skeletal muscle relaxation, minimal effect to cardiovascular/respiratory system

• irritating to tissue

• high concentration = hemolysis in ruminants and horses

barbituates

• schedule II

• cause cardiac and resp depression

• pentobarbital: short acting; treat status epilepticus, induce/maintain general anesthesia in lab animals

• phenobarbital: long acting, seizure control

isoflurane and sevoflurane

• reversible CNS depression

• liquid at room temp

• stored in vaporizer

• travel to alveoli and diffuse into blood stream

• little to no analgesia

effects of sevo and isoflurane

• dose dependent effects

• ventilation depression, CNS depression, vasodilation, hypothermia, decrease BP and perfusion, decrease HR, decrease renal blood flow

minimum alveolar concentration (MAC)

• measure of potency of a drug

• lower the MAC, more potent the drug (need lower vaporizer setting for desired effects)

• 1.5 x MAC = maintain surgical anesthesia

• 2 x MAC = maintain deep surgical anesthesia

what alters MAC

• age

• metabolism

• body temp

• disease and obesity

• pregnancy

• other anesthetic agents

common MAC values

• sevoflurane: 2.34% to 2.58%

• isoflurane: 1.3% to 1.63%

desflurane

• expensive

• MAC = 7.2% to 9.8%

• rapid induction and recovery

nitrous oxide

• mostly human medicine

• gas at room temp; no vaporizer needed

• some analgesia

• flow meter and mixed with O2

• can not exceed 70% amount

gabapentin

• anticonvulsant

• treat neuropathic pain/hypersensitivity

• for chronic pain not responding to NSAID

• cause drowsiness

• liquid may have xylitol which is toxic

trazodone

• serotonic antagonist / reuptake inhibitor

• treat behavioral disorders (anxiety/phobias)

• cause sedation, lethargy, being subdues

bupivacaine liposome injectable suspension

• BLIS / nocita

• can be splash block directly on incision

• DO NOT give IV

• long lasting up to 72 hr

• inject close to damage site

TIVA (total intravenous anesthesia)

• infusion syringe instead of vaporizer

• anesthetic drug

• administer IV with a CRI

• propofol, alfaxalone, ketamine, reversible anesthetics/sedatives

• O2 supplementation with a mask

• decreased exposure of inhalants to staff and possibility of airway irritation