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
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
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)
- 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
- 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.
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.
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
- cardiac arrhythmias
Uses of Valium. (5)
- 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
- 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?
What is Lorazepam used for?
orally in cats prior to travelling
What are the major effects of alpha-2 agonists? (3)
- muscle relaxation
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
- [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.
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.
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)