VCS 226- Anesthesia Tutoring- Premeds I & II

what are the 3 steps to the general anesthesia process

1. pre-medications

2. inductions (injectable anesthetics)

3. maintenance (inhalant/injectable anesthetics)

why do we pre-medicate?

-sedation: calm, free from anxiety

- chemical restraint

- pre-emptive analgesia- decrease drug dosage

- smooth induction/smooth recovery

- counteract side effect caused by other pre-medications

True or False: you should always trust a sedated patient

False

decreasing the dose _____increases/decreases__ the side effects

decreases

What do we hope to achieve by using a drug cocktail instead of a larger dose of one drug?

- lessening or counteracting the side effects

- decreasing cost

- shorter or absent excitement phase

What are the 5 classes of pre-med drugs?

1. Phenothiazine (major tranquilizers)

2. benzodiazepines (minor tranquilizers)

3. alpha 2 adrenergic agonists

4. opioids

5. anticholinergics

what is the most common major tranquilizer used?

acepromazine

what class of drugs is acepromazine?

phenothiazine

what is the mechanism of action for major tranquilizers?

-dopamine antagonists

-high doses have negative effects

what are the negative effects of major tranquilizers at high doses?

tremor, rigidity, catalepsy (seizure like activity)

Why do we dilute the concentration of acepromazine from 10mg/ml to 2 mg/ml

to allow greater accuracy in drug dosing- we really don't need as much as the bottle says- the bottle is 10 times the recommended dose

What is the purpose of using acepromazine

sedation: produce a "tranquil" state-

Does acepromazine have analgesia effects?

NO

What are the 3 "anti's" for acepromazine

1. antiarrythmogenic

2. antiemetic

3. antihistamine

What are the cardiovascular effects of acepromazine?

-HYPOTENSION

What can you do to treat the hypotension from acepromazine?

-reduce level of general anesthesia

-IV fluids (usually a bolus)

-1-adrenergic agonists

Why should you never use phenothiazines in breeding stallions?

it can cause penile prolapse, which can be permanent

Is acepromazine reversible?

NO

*always remember to check dosage before you give it to the patient

What is the duration of effects for acepromazine?

usually last for several hours

What is the method of elimination for acepromazine?

hepatic metabolism

*effects may be prolonged with hepatic disease or in neonate/geriatric patient

What are the other major tranquilizers besides phenothiazines?

Butyrophenones (not commonly used)

-Droperidol (similar to phenothiazines)

-Azaperone (swine)

What is the drug class name for minor tranquilizers?

Benzodiazepines

What are all of the different drugs in the class of benzodiazepines?

-diazepam

-midazolam

-zolazepam

What is the reversal for benzodiazepines?

flumazenil

What is the mechanism of action for benzodiazepines?

agonists at benzodiazepine receptor sites in the CNS; these receptors potentiate the effects of GABA (an inhibitory neurotransmitter) in the CNS

What are the clinical uses for Benzodiazepines?

-mild sedation effects

-central muscle relaxant

-useful for sedation for neonates

-good sedative in camelids and small ruminants

-potent anticonvulsants (used commonly for seizures)

Are there any cardiopulmonary effects of benzodiazepines?

In general, no

-occasional mild hypotension and respiratory depression

What is the biggest adverse effect of benzodiazepines?

excitement phase

-NEVER use the drugs alone for pre-medications

Is diazepam soluble in water?

NO

Is midazolam soluble in water?

yes

What does diazepam come dissolved in?

propylene glycol

Is propylene glycol safe for tissues?

NO- irritating to tissues

-don't give IM, always IV or rectally

Is midazolam irritating to tissues?

No, well absorbed from IM or SQ injections

Which drug, midazolam or diazepam is compatible with other solutions?

midazolam

What is the duration of action for diazepam?

up to 1 hour

What is the duration of action for midazolam?

up to 1 hour

What is the duration of action for zolazepam?

appears to be species dependent

Name all the alpha-2 adrenergic agonists

-dexmedetomidine

-xylazine

-detomidine

-medetomidine

-romifidine

-medetomidine + vatinoxan

What is the trade name for medetomidine + vatinoxan?

Zenalpha

What are the reversals for alpha-2 adrenergic agonists?

-Atipamezole (Antisedan)

-Tolazoline

-Yohimbine

What is the mechanism of action for alpha-2 adrenergic agonists?

-agonist activity at alpha-2 adrenergic receptors

- results in decrease in release of norepinephrine from adrenergic nerve terminals in CNS and periphery

What do alpha-2 adrenergic agonists do for your patient?

-produce great sedation

-excellent analgesia

-muscle relaxation

What is the biggest adverse effect for alpha-2 adrenergic agonists?

SEVERE bradyarrhythmia's

Do you treat bradyarrhythmia's in alpha-2 adrenergic agonists with atropine?

NO

What are some other cardiopulmonary effects of alpha-2 adrenergic agonists?

-biphasic blood pressure

-mild respiratory depression alone

-decrease cardiac output

-can cause stridor and dyspnea in horses and brachycephalic dogs

What are some GI side effects for alpha-2 adrenergic agonists?

-decreased GI activity

-vomiting in cats

What are some other side effects for alpha-2 adrenergic agonists?

-polyuria

-sweating

-hyperglycemia

-depressed thermoregulatory ability

-phantom kicking in horses (xylazine)

What species is the MOST sensitive to alpha-2 adrenergic agonists?

ruminants

What do you have to do to the dose of alpha-2 adrenergic agonists for ruminants?

reduce dose to 1/10th the dose of other species

What species is the least sensitive to alpha-2 adrenergic agonists?

swine

What is the duration of action of xylazine?

up to 30 mins

What is the duration of action of detomidine?

up to 2 hours

What is the duration of action of dexmedetomidine?

up to 1 hour

What dose do you usually give of atipamezole to reverse dexmedetomidine?

same volume

What is the only route that Zenalpha can go?

IM

Name all the opioids

-morphine

-hydromorphone

-fentanyl

-methadone

-meperidine

-buprenorphine

-butorphanol

-nalbuphine

-naloxone

What is the mechanism of action for opioids?

-interact with opioid receptors in the CNS

-these receptors usually have inhibitory effects on neurons

What are the 4 different categories of opioids?

-full agonist (mu, kappa)

-partial mu agonist

-agonist (kappa) & antagonist (mu)

-full antagonist

What drugs are in the full agonist (mu, kappa) category?

morphine, hydromorphone, fentanyl, methadone, oxymorphone, meperidine

What drugs are in the partial mu agonist category?

buprenorphine

What drugs are in the agonist (kappa) & antagonist (mu) category?

butorphanol, nalbuphine

What drugs are in the full antagonist category?

naloxone, naltrexone

What does the full agonist (mu & kappa agonist) do?

-produces great sedation and good analgesia

-treat moderate to severe pain

What does the partial mu agonist do?

-produce good analgesia

-DOES NOT produce good sedation

-treats mild to moderate pain

What does the agonist (kappa) antagonist (mu) do?

-DOES NOT produce good analgesia, but good sedation

-treats mild pain

-used for partial reversal of full agonist opioid

What do the full antagonists do?

reverse sedation and analgesia completely

What are the cardiopulmonary effects of opioids?

-bradyarrhythmia

-respiratory depression(panting)

-histamine release

What is the 3P effect of opioids?

poop, pee, puke

Hydromorphone duration

2-4 hours

Morphine duration

2-4 hours

Morphine side effects in cats and horses?

-morphine mania in cats

-may cause excitation

Fentanyl duration

-SHORT, only 10-15 mins

-usually given as CRI

What other ways can you give fentanyl?

-dermal patch

-lasts 72 hours

Methadone duration?

2-4 hours, usually redose every 2 hours intra-op

What do we usually combine methadone with to use as a neuroleptanalgesia?

acepromazine

Buprenorphine duration

6-8 hours

What is Zorbium?

-buprenorphine transdermal

-cats ONLY

-up to 4 days of pain control

-for surgery, apply 1-2 hours before

What is the butorphanol duration?

1-2 hours

What are the anticholinergic drugs?

-atropine

-glycopyrrolate

What is the mechanism of action for anticholinergic drugs?

Competitively block the action of acetylcholine on

What are the clinical uses of anticholinergic agents

-inhibit or treat bradyarrhythmia's

-decrease secretions (used for dentals)

-prevent or block adverse effects of other drugs

What is the onset and duration of atropine?

fast onset, slow duration (60-90 mins)

What is the onset and duration of glycopyrrolate ?

slow onset (15 mins), longer duration (2-4 hours)

What are the adverse effects of anticholinergics?

-initial bradyarrythmias

-sinus tachycardia

-colic in horses

Which anticholinergic is less arrhythmogenic?

glycopyrrolate

What is the definition of neuroleptanalgesia?

a state of quiescence, altered awareness, and analgesia produced by the administration of a combination of a neuroleptic agent and a narcotic(opioid) analgesic

What are the combinations for neuroleptanalgesia?

any combination of opioid + tranquilizer is possible