7/8: Preanesthetic Meds Flashcards
What are advantages of using anticholinergics as part of pre-anesthetic meds?
Prevention of salivation, airway secretions, bradycardia
What are advantages of using maropitant as a pre-anesthetic med?
Prevention of nausea and vomiting;
It also provides adjuct analgesia (NK-1 antagonist) and decreases inhalant requirements
What are 5 general advantages to using pre-anesthetic meds?
- Chemical restraint
- Decreased stress/anxiety –> decreased catecholamines –> decreased risk of arrhythmias
- Decreased induction and inhalant anesthetic doses
- Pre-emptive analgesia
- Smooth recovery
What is pre-emptive analgesia?
Treatment initiated before surgery in order to prevent the establishment of central sensitization evoked by incisional and inflammatory injuries occurring during surgery and in the early post-op period.
What are 4 disadvantages to using pre-anesthetic meds?
- Bradycardia
- Hypotension
- Excitement/dysphoria
- Nausea/vomiting
What pre-anesthetic med types cause bradycardia?
Alpha-2 agonsists, opioids
What pre-anesthetic med types cause hypotension?
Acepromazine, alpha-2 agonists
What pre-anesthetic med types cause excitement/dysphoria?
Opioids, benzos
What pre-anesthetic med types cause nausea/vomiting?
Mu-agonist opioids, dexmedetomidine
What are 6 factors to consider when selecting a pre-anesthetic medication?
- Species
- Health status of patient
- Pain (existing and expected)
- Temperament
- Duration of procedure
- Anticipated side effects of drugs administered
What 4 drug types can be used as analgesics?
- Opioids
- Dissociatives
- NSAIDs
- Alpha-2 agonists, maropitant
What 2 drugs can be used as anticholinergics?
- Atropine
- Glycopyrrolate
What 3 drug types can be used as tranquilizers/sedatives (neuroleptics)?
- Phenothiazines
- Alpha-2 agonists
- Benzos
What 3 categories of drugs are used for premeds?
Opioids, sedatives/tranquilizers, anticholinergics
What 5 opioid drugs are pure mu agonists?
- Hydromorphone
- Fentanyl
- Morphine
- Methadone
- Oxymorphone
What opioid drug is a mixed kappa agonist/mu antagonist?
butorphanol
What opioid drug is a partial mu agonist?
Buprenorphine
What opioid drugs are full mu antagonists?
Naloxone, naltrexone
What are the 3 opioid receptors?
mu, kappa, delta
Where are opioid receptors located?
In peripheral and central nervous systems
What is the mechanism of action for opioids?
Opioid receptors are coupled with inhibitory G-proteins (GPCRs) which activate 2nd messenget systems in cells
What are the 2nd messenger systems that are activated by G-proteins?
- Closing of Ca channels
- Efflux of K –> hyperpolarization
- Decreased cAMP production
What are 4 overall results that opioids have on cells?
- Hyperpolarization
- Decreased neuronal excitability
- Decreased neurotransmitter release
- Decreased transmission of nerve impulses
Naxolone is such a weak mu _____ that we consider it an _____.
agonist, antagonist
Effects of mu/kappa agonists are _____ dependent, and there is no _____ effect.
dose, ceiling
What are some clinical side effects cause by mu agonists?
- Analgesia
- Inhalant sparing
- Mild to profound sedation
- Bradycardia
- Respiratory depression
- GI: nausea, vomiting, decreased motility
- Urinary retention
- Hyperthermia in cats
What does it mean if a drug has a ceiling effect?
Increased dose does not = increased analgesia
What 2 opioid types have a ceiling effect?
Partial mu agonists (Buprenorphine)
K agonist/mu antagonist (Butorphanol)
What can Butorphanol be used with?
Dexmedetomidine
What type of analgesia do opioids provide?
Somatic and visceral
When do opioids provide mild sedation?
When used alone
What mild CV effects do opioids have?
- Decreased HR due to increased vagal tone –> anticholinergic
- Little/no effect on vasculature (histamine release)
- Little/no effect on cardiac contractility
Opioids _____ the MAC of inhalant.
decrease
When should you use full mu agonists?
With moderate to severe pain
What is the duration of action of hydro/oxymorphone?
2-4 hours
What is the duration of action of morphine/methadone?
4-6 hours
Methadone is an NMDA _____.
antagonist
What effects can morphine have on vasculature?
Histamine release
A side effect of full mu agonists is ______ to ______ analgesia.
moderate, severe
What is a CV side effect that mu agonists cause?
bradycardia
What GI side effects do mu agonists cause?
Nausea, vomiting, defecation
What do mu agonists cause in cats specifically? (side effect)
hyperthermia
What can you give together with hydromorphone to mitigate the side effects?
fentanyl
What type of drug is fentanyl?
pure mu agonist
What is the duration of fentanyl?
15-30 min
What is done to mitigate the short duration of fentanyl?
Given IV as a CRI
What is a CV side effect of fentanyl?
Bradycardia (> other mu agonists)
What are GI side effects of fentanyl?
No vomiting; may cause nausea
Fentanyl can cause respiratory _____.
depression
What should be monitored intra-op when fentanyl is on board?
EtCO2, IPPV
What should be monitored post-op when fentanyl is on board?
SpO2
What are 3 ways that we use fentanyl?
- Induction agent in critically ill SA patients
- Intra-op and post-op CRI
- Patch (post-op)
Buprenorphine produces _____ sedation, and _____ to _____ analgesia.
mild, mild, moderate
What is the onset of buprenorphine?
30-45 min (slow)
What is the duration of buprenorphine in dogs and cats?
Dogs = 4-10 hours
Cats = 6-12 hours
Buprenorphine has a strong _____ for the mu receptor.
affinity
When should you not use buprenorphine as a pre-med?
If the procedure is painful
What is a disadvantage of buprenorphine?
It is difficult to reverse
What is the SA dose of buprenorphine?
0.01 - 0.04 mg/kg
How does buprenorphine compare to mu agonists?
It has LESS:
- Respiratory depression
- Panting
- Bradycardia
- Analgesia, MAC sparing
- No nausea, vomiting
What is the new, long acting formulation of buprenorphine approved for cats?
Simbadol - 0.24 mg/kg SQ SID
Because butorphanol is a mu antagonist, it is a partial _____ _____.
reversal agent
Butorphanol provides _____ sedation and analgesia.
mild
How long does sedation with butorphanol last? Analgesia?
Sedation = 1-2 hours
Analgesia = ~90 min
How does butorphanol compare to mu agonists?
It has LESS:
- Respiratory depression
- Panting (seen at higher doses)
- Bradycardia
- Analgesia, MAC sparing
- No nausea/vomiting
What does butorphanol prevent that dexmedetomidine causes?
nausea/vomiting
What type of procedure should butorphanol be used for?
Sedation for non-painful procedures (i.e. x-rays)
How is butorphanol used in dogs and cats?
Alone (dogs) or with sedative/tranquilizer
What is the dose for butorphanol?
0.2 - 0.4 mg/kg
How should butorphanol be used in horses?
With alpha-2 agonist for pre-med/intra-op
How should butorphanol be used in large ruminants? Small ruminants?
Large = during/after induction (vocalization)
Small = as premed + benzodiazepine
What are the 4 sedatives/tranquilizers used?
- Acepromazine
- Alpha-2 agonists
- Benzodiazepines
- Dissociatives - not sedatives but used for chemical restraint
What is an alpha-2 agonist used in SA?
Dexmedetomidine
What are 3 alpha-2 agonists used in LA (primarily horses)?
- Xylazine
- Detomidine
- Romifidine
What are 2 common benzodiazepines used?
Midazolam and Diazepam
What are 2 dissociatives used for chemical restraint?
- Ketamine
- Tiletamine (in Telazol)
What type of drug is acepromazine?
Phenothiazine
What does acepromazine do cellularly?
Blocks dopamine, 5-HT, and alpha-1 adrenergic receptors
What anatomical locations does acepromazine act on?
Basal ganglia, hypothalamus, limbic system, brain stem, reticular activating system (RAS)
Why is acepromazine an effective tranquilizer?
It blocks D and 5-HT Rs –> depression of brain stem and RAS connections to cerebral cortex
How does acepromazine affect the vessels?
Causes vasodilation through an alpha-1 adrenergic blockade
What CV effects does acepromazine have?
- Decreased symp tone (sinus bradycardia, 2nd deg AV block)
- “Anti-arrhythmic” effect - cardiprotectant
What respiratory effect does acepromazine have?
resp depression
Ace _____ nausea/vomiting through ___ receptors in the chemoreceptor trigger zone.
decreases, D
What effect does ace have on PCV?
Decreased due to splenic sequestration
What effect does ace have on platelets?
Altered plt function
What effect does ace have on body temp?
Hypothermia (peripheral vasodilation or effects on hypothalamus, redist of blood from core to periphery)
Ace does not have _____ effects BUT has synergistic effects with _____.
analgesic, opioids
Ace _____ induction dose and MAC of inhalant.
decreases
Ace produces _____ to _____ sedation.
mild, moderate
What is the onset of action of ace?
~20-30 min
What is the duration of ace?
4-6 hours
T/F: Ace has a reversal agent
False
Where is ace metabolized and excreted?
Metab in the liver, excreted by kidney
What can happen if ace is accidentally injected into the carotid in horses?
Seizures and death
Why should ace not be used for allergy testing?
Blocks histamine
What are 3 contraindications for ace use?
- Moderate/severe liver dysfunction
- Hypovolemia, shock, critically ill patients
- Paraphimosis in stallions –> relaxation of penis retractor muscle via alpha-1 blockade
What dogs cannot have ace?
Those with a mutation in the ABCB1/MDR1/P-gp gene (i.e collies)
How can ace be administered?
PO, SQ, IM, IV
What is the dosage for ace?
0.005 - 0.02 mg/kg IM or IV
What is the alpha-2 to alpha-1 receptor ratio?
1600:1
What are the 3 isoreceptors of alpha-2 drugs?
Alpha-2A, alpha-2B, alpha-2C
What type of receptor are alpha-2 receptors?
GPCR
Where is the alpha-2A receptor and what is its effect?
In locus ceruleus (brain) –> inhibition –> sedation, anxiolysis, sympatholytic properties
Where is the alpha-2B receptor and what is its effect?
In vasculature –> excitatory –> vasoconstriction
Where are therer both alpha-2B and 2C receptors and what is their effects?
Dorsal horn of spinal cord –> inhibit nociception
What are the biphasic CV effects of alpha-2 agonists?
- Initial hypertension (10-30 min) response due to peripheral alpha-2B stim with vasoconstriction
- Central alpha-2A stim –> decreased NE –> hypotension due to bradycardia and peripheral vasodilation
In relation to alpha-2 agonists:
Initially, bradycardia is a _____ mediated response due to increased BP, while decreased _____ slows HR in latter phase.
baroreceptor, sympathetic outflow
What is the treatment for alpha-2 agonist induced bradycardia that has a normal to high BP and why?
No treatment necessary because anti-cholinergics will increase BP too much and can cause retinal hemorrhage and detachment.
What is the treatment for alpha-2 agonist induced bradycardia that has a low BP and why?
Treatment with anti-cholinergic indicated ~ 1 hour after administration due to central alpha-2A sympatholytic effect
What are 3 uses for dexmedetomidine?
- Premed (dogs and cats)
- Intra-op CRI (dogs, cats, horses)
- Sedation for recovery (dogs and cats)
What is the dosage for dexmedetomidine as a premed?
5.0 - 10 mcg/kg
(Lower end in dogs, higher end in cats)
What is the analgesic/sedative effect of dexmedetomidine?
potent and dose-dependent
What is the onset of dexmedetomidine?
Rapid (~5 min)
What is the duration of action of dexmedetomidine?
Short (~30-60 min, dep on dose)
What is the dosage for dexmedetomidine as an intra-op CRI?
1.0 - 2/0 mcg/kg/hr
What is the dosage for dexmedetomidine when used in sedation for recovery?
0.5 - 1.0 mcg/kg IV
What CV effects does dexmedetomidine have?
40% decrease in CO, reflex bradycardia due to vasoconstriction
(Can decrease chance of heart attack post-op in humans)
Can dexmedetomidine be reversed?
Yes - Atipamazole (Antisedan®)
What type of patient should dexmedetomidine be reserved for?
Healthy or very painful, fearful, aggressive patients
What can be added to dexmedetomidine if the patient is unhandleable after administration?
Ketamine 1.0 - 2.0 mg/kg
What alpha-2 agonists can be used in horses? What are the reversals?
Xylazine, Detomidine, Romifidine;
Reversals = yohimbine, tolazoline
What is the cellular effect/method of action of Benzodiazepines?
Enhance effect of ntm GABA at the GABAA receptor –> increase Cl into cell –> hyperpolarization
What can benzodiazepines be used for, generally?
Sedation, hypnosis, anxiolysis, amnesia, anticonvulsant, muscle relaxant
What are 2 benzodiazepines that are commonly used?
Diazepam and Midazolam
Diazepam and midazolam typically are NOT good _____ in young, healthy dogs and cats. What can they be used for?
sedatives;
Diazepam = tx of seizures
Midazolam = premed
What do Diazepam and Midazolam do that we do not want to happen?
Cause paradoxical excitement, hyperresponsiveness
What animals experience more profound sedation with BDZ?
Pediatric (<3 mos), geriatric, critical, small ruminants, neonatal foals
What is the severity of CV effects of BDZ?
mild
What is the respiratory effect of BDZ?
Enhances resp depression of other drugs
Where are BDZ metabolized?
Liver - both have active metabolites
What is the 1/2 life of diazepam in dogs? Cats? Horses?
Dogs = 2-4 hours
Cats = 5.5 hours
Horses = 7-22 hours
What is the 1/2 life of midazolam in dogs? horses?
Dogs = ~70 min
Horses = ~3-6 hours
What do BDZ NOT provide?
analgesia
What does diazepam contain that can cause issues?
Propylene glycol;
Pain on injection, not well absorbed, toxic at high doses
What is the relative cost of midazolam and diazepam?
Relatively similar
What do we use midazolam with in dogs and cats?
With an opioid for premed in very young, geriatric, or sick patients
What is the dosage for midazolam in dogs and cats?
0.1 - 0.2 mg/kg IM or IV
What induction agent dose can be reduced if midazolam is used as an adjunct with it in dogs and cats?
propofol
What drug is midazolam used as a co-induction agent with in adult horses?
ketamine
What drug is midazolam used as a co-induction agent with in neonate horses?
Butorphanol
What drug is midazolam used as a co-induction agent with in small ruminants?
Ketamine or Propofol
What is the method of action of anti-cholinergics?
Antagonize ACh at muscarinic Rs at post-ganglionic sites in parasympathetic nervous system (increases sympathetic tone)
What do anti-cholinergics do to vagal effects and salivary secretions?
Decreases them
What are anti-cholinergics primarily used for?
To counter vagal effects of anesthetic drugs
What are the 2 most common anti-cholinergics?
Atropine and Glycopyrrolate
What effect do anti-cholinergics have on the heart rate?
Increases it
What effect do anti-cholinergics have on salivation?
Decreases it
What effect do anti-cholinergics have on mucociliary transport/clearance?
Decreases it
What effect do anti-cholinergics have on the pupils?
Dilates them (atropine)
What effect do anti-cholinergics have on GI motility in LA?
Decreases it; relaxation of gastro-esophageal sphincter
What effect do anti-cholinergics have on blood flow?
Decreases it –> myocardial ischemia/hypoxemia
What heart conditions can anti-cholinergics be used to treat?
Sinus bradycardia, 1st and 2nd deg AV block, sinus arrest, CPCR
What is the onset of action of atropine?
<5 min IM
<1 min IV
What is the duration of action of atropine?
~30 min IV
What is atropine capable of crossing?
BBB/placenta;
Reason some people don’t like to use it in C-sections
What is atropine more likely to cause than glycopyrrolate?
Sinus tachycardia
T/F: Glycopyrrolate crosses BBB/placenta
False
What is the onset of action of glycopyrrolate?
3-5 min
What is the duration of action of glycopyrrolate?
2-4 hours
Why should glycopyrrolate be avoided in LA?
GI stasis
What are 2 approaches for use of anti-cholinergics in SA?
- Pre-treatment (expense, risk of tachycardia)
- Treat if needed (monitor HR, rhythm, BP)
What 4 cautions should be taken when considering an anti-cholinergic?
- LA
- Geriatric patients or those with heart disease
- Patients with low HR/high BP (dexmedetomidine)
- Ineffective in patients with moderate/severe hypothermia
What are 3 considerations for an individualized anesthesia and analgesia plan that includes a preanesthetic?
-
Opioid Analgesic - butorphanol, buprenorphine, full mu agonist (or fentanyl IV)
- Based on spp, pain, inhalant sparing needs, cost, availability
-
Tranq/Sedative - acepromazine, alpha-2 agonist, BDZ, GG
- Based on signalment, temperament, physical status, co-morbidities
- +/- Anti-cholinergic