-
Describe neuroleptanalgesic technique.
combination of a sedative or tranquilizer and and opioid (Ex. dex-dom + butorphanol as pre-med)
-
What is the mechanism of action of anticholinergic drugs?
compete with Ach for access to muscarinic cholinergic receptors (NOT nicotinic)--> block effects of Ach at the post-ganglionic parasympathetic nerve terminal
-
What are reasons for using anticholinergic drugs? (3)
- decrease glandular secretions in airways, mouth, GI
- inhibit bradycardic effects of vagal stimulation
- induce mydriasis (ophtho)
-
What are the respiratory effects of anticholinergics? (3)
- reduce secretions of respiratory tract
- drying of secretions decreases efficiency of mucociliary apparatus
- bronchodilation
-
What are the GI effects of anticholinergics? (4)
- increased pH of gastric contents
- volume of gastric contents decreases
- intestinal motility decreases or is eliminated for several hours
- antiemetic
-
Why don't we use anticholinergics in horses?
cause paralytic ileus and colic
-
What are the cardiovascular effects of anticholinergics?
inhibit vagal stimulation (affects SA node then AV node)
-
Describe the sequence of effects of atropine administration IV. What is the clinical implication of this?
- SA discharge rate increases--> +/- transient secondary AV block--> AV node responsiveness increases--> rate of ventricular contraction increases
- transient second degree AV block, takes a while for the AV node to catch up with the SA node (affected first) so it seems the bradyarrhythmia gets worse at first
-
What are causes for increases in vagal stimulation? (3)
- traction on visceral orans during surgery
- pressure or traction on the extraocular muscles
- certain drugs (opioids, alpha2 agonists, digitalis, IV calcium)
-
Why might atropine not be effective for bradycardia induced by inhalant anesthetics?
inhalants cause a withdrawal of sympathetic tone, causing the HR to decrease (NOT an increase in vagal tone); atropine blocks vagal stimulation
-
What are potential adverse effects of anticholinergic administration? (5)
- sinus tachycardia
- increased myocardial oxygen consumption
- can precipitate heart failure and pulmonary edema in patients with CV dz
- bloat in ruminants
- colic in horses
-
Contrast atropine from glycopyrrolate.
- Atropine: rapid action, crosses BBB, crosses placenta
- Glycopyrrolate: twice as potent, long-acting, does not cross BBB, does not cross placenta
-
What is Scopolamine?
- anticholinergic; less potent than atropine and glycopyrrolate
- decreased secretions
- not commonly used
-
What is Buscopan?
- anticholinergic/ scopolamine derivative
- antispasmodic, decreased GI secretions
- short duration
- transient increase in HR
-
When is Buscopan used?
horses with spasmodic colic (this is the exception to never using anticholinergics in large animals)
-
What are indications to use anticholinergics? (5)
- to prevent or treat drug-induced bradycardia
- when excessive salivation is anticipated
- brachycephalic breeds
- prevent bradycardia in neonates
- to accompany anticholinesterase reversal of neuromuscular blockade
-
What drugs can cause drug-induced bradycardia? (2)
- alpha-2 agonists
- some opioids
-
Why is it commonplace to give anticholinergics to brachycephalic dogs during surgery?
they have higher resting vagal tone or the potential for higher vagal tone
-
Why is it so important to prevent bradycardia in neonates?
neonates' CO is dependent upon HR (rigid non-compliant ventricles of neonates do not allow increase in SV when HR is low)
-
What are the 3 phenothiazine trnquilizers?
acepromazine, chlorpromazine (thorazine), promazine (sparine)
-
What is the mechanism of action of phenothiazine tranquilizers?
blockade of dopamine receptors in the limbic system and basal ganglia
-
What are effects of acepromazine? (4)
- calming
- muscle relaxation
- third eyelid prolapse
- reduces amount of injectable and inhalant anesthetic needed
-
What are cardiac and vascular side effects of acepromazine? (6)
- alpha-1 adrenergic blockade--> causes vasodilation of arteries and veins--> decrease BP and hypothermia
- decreased ventricular arrhythmias (ie. quinidine is anti-arrhythmic)
- decreased PCV and WBC count
-
What is the therapy for a hypotensive crisis after acepromazine? (2)
- IV fluids
- phenylephrine (alpha-1 agonist)
-
Why do you NOT give epinephrine to an animal in hypotensive crisis after acepromazine?
["epinephrine reversal"] as an alpha-1, alpha-2, beta-1, and beta-2 agonist, it produces a paradoxical drop in BP (alpha receptors are already blocks then epi binds beta-2 receptors, causing further vasodilation)
-
How does ace affect HR?
- little to no effect
- Boxers- bradycardia (central effect)
-
Why does ace cause decreased PCV and WBC counts?
margination of red cells within vasculature and relaxation of splenic capsule due to alpha-1 blockade
-
What are the respiratory effects of ace? (2)
- decrease respiratory rate
- (low doses) tidal volume increases
-
In what cases is acepromazine contraindicated and why? (5)
- severe liver disease: ace undergoes hepatic metabolism--> compromised liver--> prolonged sedation
- coagulopathy: inhibit platelet aggregation
- epilepsy
- hypovolemia
- anemia
- reduce dose for very young animals (not contraindicated, just decrease dose)
-
Acepromazine is known to have _________ effects by blockade of DA receptors in the medullary CTZ.
antiemetic
-
Why shouldn't we use ace during allergy testing?
it has antihistamine effects
-
Acepromazine does NOT produce ___________ effects.
analgesic (may enhance analgesic effects of other drugs)
-
Why might you avoid using ace in breeding stallions?
causes penile prolapse (usually temporary- good for cleaning sheath)--> may become persistent- paraphimosis
-
____________ has been thought to lower the seizure threshold and should not be used in animals with a hereditary predisposition or organic brain disease.
Acepromazine
-
What is the most effect tranquilizer in swine?
Azaperone (Stresnil)- used as an aid in mixing and sorting
-
What are properties of the benzodiazepines? (5)
- minimal tranquilization/ less potent in animals than people
- mild calming in older animals
- can produce dysphoria
- muscle relaxation
- effects are supra-additivewwith general anesthetics
-
What commons drugs are members of the Benzodiazepine class? (4)
- Diazepam (Valium)
- Midazolam (Versed)
- Zolazepam (Telazol)
- Lorazepam (Ativan)
-
What is the mechanism of action of benzodiazepines? (5)
- stimulate benzdiazepine receptors in the CNS, which are a part of the GABA receptor complex
- hyperpolarize membranes by increasing Cl- conduction and increased threshold for stimulation
- enhance GABA, which is inhibitory
- depress limbic system, thalamus, and hypothalamus
- reduce polysynaptic activity in brain in spinal cord
-
Are there cardiopulmonary effects of benzos? (3)
- minimal decrease in BP
- rarely produce brady cardia
- minimal effects on ventilation
- [this is why we commonly choose these drugs for patients with cardiovascular compromise]
-
Fast IV injection of Diazepam can cause... (4)
- depression of myocardial activity
- hypotension
- bradycardia
- cardiac arrhythmias
-
Uses of Valium. (5)
- anticonvulsant
- useful in sick/ debilitated animals for premed
- combined w/ ketamine to produce short term hyponosis
- augment muscle relaxation (esp in horses)
- stimulate appetite in cats and ruminants
-
What are the disadvantages of Diazepam? (1)
does not mix in same syringe with other drugs (except ketamine)
-
What are adverse effects of benzos? (5)
- diazepam may cause pain on injection into muscle and peripheral veins
- ataxia (LA)
- dysphoria in young active animals
- occasional excitement in animals
- may release suppressed behavior (biting)
-
Properties of Midazolam. (3)
- similar to diazepam in potency but water-soluble (unlike valium)
- can be mixed with other drugs in same syringe
- no sting or tissue irritation with IM route
-
Properties of Zolazepam. (3)
- more potent and longer-lasting that diazepam
- one of two drugs contained in telazol
-
What are the advantages of TKX? (3)
- good muscle relaxation
- analgesia
- useful in feral cats and pigs for general anesthesia
-
What are components of TKX, and what are 2 major disadvantages of this?
- telazol, ketamine, xylazine
- telazol can cause prolonged and unpredictable recoveries
- telazol is not reversible
-
What is the reversal for benzos?
Flumazenil (Romazicon)
-
What is Lorazepam used for?
orally in cats prior to travelling
-
What are the major effects of alpha-2 agonists? (3)
- sedation
- muscle relaxation
- analgesia
-
What drugs in vet med are alpha-2 agonists? (4)
- xylazine (horses, dog, cats, deer)
- detomidine (horses)
- dexmedetomidine (dogs, cats)
- romifidine (horses)
-
What is the mechanism of action of alpha-2 agonists?
- produce CNS depression by stimulating alpha-2 receptors in the CNS and peripherally--> reduce release of excitatory neurotransmitters (NE)
- muscle relaxation occurs from inhibition of polysynaptic reflexes in the spinal cord
-
What are the vascular effects of alpha-2 agonists? (3)
- peripheral vasoconstriction
- hypertension
- [due to extrasynaptic vascular alpha-2 receptor stimulation and some small degree of alpha-1 stimulation]
- pale MMs
-
What are cardiac effects of alpha-2 agonists? (4)
- decreased HR
- 1st and 2nd degree AV blocks (rarely 3rd degree)
- [due to increased vagal tone! and decreased sympathetic tone centrally (due to decreased NE release)]
- decreased CO
- decrease in inotropy
-
Initial hypertension with alpha-2 agonists is ________ in duration when combined with xylazine; it is __________ in duration when combined with detomidine or dexmedetomidine.
shorter; longer
-
What are respiratory effects with alpha-2 agonists? (5)
- respiratory depression (respiratory center sensitivity to CO is decreased)
- decreased resp rate
- increased tidal volume (PaCO2 and PaO2 remain relatively normal)
- respiratory stridor and dyspnea due to relaxation of muscles of the nostrils (BE CAREFUL IN BRACHYCEPHALICS AND HORSES)
- pulmonary macrophage infiltrates and hypoxemia in sheep (V/Q mismatch)
-
What are GI side effects of alpha-2 agonists? (6)
- suppress sailvation and GI secretions
- decrease or abolish GI motility (transient colic in horses, predispose to bloat in large dogs and cattle)
- vomiting in dogs and cats
- suppress swallowing reflex
- decrease insulin secretion
- excellent relief of GI pain in horses
-
_________ is the most effective emetic in cats.
Xylazine
-
What are renal effects of alpha-2 agonists? (2)
- inhibit tubular reabsorption of sodium
- produce diuresis
-
How are alpha-2 agonists administered?
rapid absorption after IM, SQ, and IV injection
-
In dogs and cats, xylazine can lead to... (3)
severe bradycardia and bradyarrhythmias, vomiting, profound sedation.
-
In horses, xylazine is used for... (5)
sedation, muscle relaxation, treating colic pain, "head down posture", caudal epidural anesthesia
-
What is unique abut using xylazine in ruminants? (2)
- 100x more potent than in horses or dogs
- produced oxytocin-like response (premature parturition in near term cows, milk let down)
-
Dexmedetomidine is _____________ than xylazine.
more potent and longer-lasting
-
What are reversal agents for alpha-2 agonists? (5)
antisedan, yohimbine, tolazine, doxapram, atipamezole
-
How are reversal for alpha-2 agonists administered?
IM (can cause hypotension and excitement if given too rapidly IV)
|
|