36 terms

Anesthesia

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Preanesthetic Evaluation
1. presentation and history
2. physical exam
3. laboratory tests
4.diagnostic procedures
5. pain assessment
6. physical status
Classes of premed drugs
Anticholinergis
phenothiazines
alpha-2
benzodiazepines
opiods
which anticholinergic drug has a longer onset and duration
...
which anticholinergic drug crosses the BBB
Atropine

central parasympatholytic actions
anticholinergics cause clinically significant ileus in___________
Horses

Clinical effects: biliary, gastrointestinal, smooth muscle relaxation
2 types of anticholinergics
Tertiary=atropine sulfate

quaternary amine= glycopyrrolate (rubinul)
MOA of Anticholinergics
compete with actions of ACh at muscarinic post ganglionic cholinergic sites

drugs that cross the BBB have central parasympatholytic actions
Clincial effect of Anticholienrgics
-HR: increases
-RR: broncho dilation (asthmatic patients, COPD)

-Decrease bronchial and oral secretions
-Raise stomach ph
-Mydriatic, cycloplegic
-biliary, GI, Smooth muscle relaxation (ileus in hrose)
On set of action of Anticholinergics
Atropine: 30 seconds to min after IV

Glycopyrrolate: 1-2 min after IV
Duration of action of anitcholinergics
Atropine: 15-20 min after IV

Glycopyrrolate: 30min-1 hour after IV
anticholinergic clinical use in dogs and cats
Counter opioid induced bradycardia

counter secretions associated with the use of 'dissociative' drugs (ketamine)
would you use the low or high end of the dose ( or no) atropine premedication prior to induction with ketamine in a dog or cat
...
Atropine in rabbits and ruminants
Rabbits have atropinase

rumen microflora may render atropine ineffective

Administration of preanesthetic medications is routine in rabbits and rodents. Parasympatholytics will decrease vagal tone as well as the amount of bronchial and salivary secretions. Atropine (0.05 mg/kg SQ; 0.08 mg/kg SQ in rabbits) or glycopyrrolate (0.01 to 0.02 mg/kg SQ or IM; 0.01-0.1 in rabbits) can be used. Atropine has a more rapid onset and is recommended for treating bradycardia and cardiac emergencies while glycopyrrolate is more slowly absorbed but has a longer duration. Up to 50% of rabbits have plasma atropinesterase and the dose is higher and it must be given more frequently. As a preanesthetic, glycopyrrolate is preferred in rabbits. These drugs can thicken respiratory secretions which can obstruct the airway.

ruminants:Anticholinergics such as glycopyrrolate and atropine tend to cause the saliva of the small ruminant to become thick and harder to expel from the mouth as well as decreasing gut motility, so they are avoided unless the patient exhibits severe bradycardia. Then atropine can be given at a dose of 2mg/50kg IM or SQ
?
phenothiazine classification
tranquilizers or ataractics
-relieve anxiety without producing undue sedation
MOA of phenothiazines
antagonize central and peripheral NE and dopamine

-excitatory neurotransmitters

-relevance: tranquilization, hypotension, bradycardia..

paraphimosis in breeding stallions
behavioral/anesthetic effects of Phenothiazines
potentiates other sedative

ace in the dog reduces MAC(minimum alveolar conentrations) of halothane by 40%
cardiovascular effects of phenothiazines
-hypotension is common

-effect on heart rate variable

-protect against epinephrine(catecholamine) induced dysrhythmias
respiratory effects of phenothiazines
-decreased respiratory rate
*compounded with other drugs like opioids

-tidal volume unchanged
Phenothiazines effect on blood
-decreased hematocrit and plasma protein
*hemodilution
*splenic sequestration

-clotting times prolonged

-anti-platelet?
Duration of phenothiazines
Acepromazine:
peak effect:
5-15 min IV
30-45 min IM

-Duration=3-6 hours
Clinical application of phenothiazines
1. active or anxious patient
(pre or post op)

2. treat hypertension

3. cautious use with seizures

4. cautious use in stallions

5.avoid in 'shocky' patients
?
phenothiazine derivatives are know to antagonize...
dopamine actions in the limbic, hypothalamic and mesocortical region of the brain
Alpha 2 agonists least potent to most potent
Least potent=Xylazine(requires highest dose)
What kind of dysrhythmias are observed with alpha-2 agonist drugs
Bradycardic dysrhythmias
Behavioral effects of alpha 2 agonists
-Sedation
-animals may become aroused in response to stimuli
biting, phantom kicking
-reduction in injectable anesthetics
-reduction in inhaled anesthetics dose
-analgesia (short lived)
dose differences between species: Alpha 2 agonists
Cow
Llama
Horse
Dog
Cat
Pig


CLHDCP
(1/10)cow-llama-horse-dog-cat-pig(4mg/kg)
Alpha 2 agonist: Cardiovascular effects
Horse: hypertension from vasoconstriction->hypotension

Dog: longer hypertensive phase with newer drugs

bradycardia and decreased CO

Bradysrhythmmias
*2nd degree A-V block

{pre-emptive atropine NOT good}
GI effects of Alpha-2 agonists
emesis in cats(xylazine)

hyperglycemia
diuresis
Clinical application of alpha-2s
-outpatient sedation
-fractious sedation
-routine premed in HORSE
-epidural use in horses/cattle
Rodeo horse with laceration;cant handle.

1. which alpha 2 agonist will you use via pole syringe?

2. what can you sue to enhance the reliability of sedation?
1. IM detomadine. potency, IM has the smallest volume for equivocal sedative dose.

2. give with opioid like butorphenol (torb)

ex: Dorm+torb
5 yr healthy bichon, well sedated for rads with dexmedetomidine and butorphanol IM. has bluish mucus membranes, whats going on?
cardiac output is slow. the O2 is used up faster than the blood can deliver it.

dexmedetomidine causes decreased CO, peripheral vasoconstriction, profound bradycardia.
Alpha 2 ANTAgonists
reversal of alpha 2 agonists

1. yohimbine
2. atipamezole
3. idazoxan
4. tolazoline
precautions of alpha 2 antagonists
anxiety
increased HR
increased BP
skin flushing,
nausea
diarrhea
hyperthermia
sudden death!!!
Peripheral antagonists of alpha 2s
Alpha 2 agonists cause peripheral vasoconstriction. Vatinoxan is being studied to revers the peripheral effects (hypertension, bradycardia)

while maintaining central effects (sedation/analgesia)