Anesthesia1- Pre-Anesthetic

combination of a sedative or tranquilizer and and opioid (Ex. dex-dom + butorphanol as pre-med)

compete with Ach for access to muscarinic cholinergic receptors (NOT nicotinic)--> block effects of Ach at the post-ganglionic parasympathetic nerve terminal

• decrease glandular secretions in airways, mouth, GI
• inhibit bradycardic effects of vagal stimulation
• induce mydriasis (ophtho)

• reduce secretions of respiratory tract
• drying of secretions decreases efficiency of mucociliary apparatus
• bronchodilation

• increased pH of gastric contents
• volume of gastric contents decreases
• intestinal motility decreases or is eliminated for several hours
• antiemetic

cause paralytic ileus and colic

inhibit vagal stimulation (affects SA node then AV node)

• 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

• traction on visceral orans during surgery
• pressure or traction on the extraocular muscles
• certain drugs (opioids, alpha2 agonists, digitalis, IV calcium)

inhalants cause a withdrawal of sympathetic tone, causing the HR to decrease (NOT an increase in vagal tone); atropine blocks vagal stimulation

• sinus tachycardia
• increased myocardial oxygen consumption
• can precipitate heart failure and pulmonary edema in patients with CV dz
• bloat in ruminants
• colic in horses

• Atropine: rapid action, crosses BBB, crosses placenta
• Glycopyrrolate: twice as potent, long-acting, does not cross BBB, does not cross placenta

• anticholinergic; less potent than atropine and glycopyrrolate
• decreased secretions
• not commonly used

• anticholinergic/ scopolamine derivative
• antispasmodic, decreased GI secretions
• short duration
• transient increase in HR

horses with spasmodic colic (this is the exception to never using anticholinergics in large animals)

• 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

• alpha-2 agonists
• some opioids

they have higher resting vagal tone or the potential for higher vagal tone

neonates' CO is dependent upon HR (rigid non-compliant ventricles of neonates do not allow increase in SV when HR is low)

acepromazine, chlorpromazine (thorazine), promazine (sparine)

blockade of dopamine receptors in the limbic system and basal ganglia

• calming 
• muscle relaxation
• third eyelid prolapse
• reduces amount of injectable and inhalant anesthetic needed

• 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

• IV fluids
• phenylephrine (alpha-1 agonist)

["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)

• little to no effect
• Boxers- bradycardia (central effect)

margination of red cells within vasculature and relaxation of splenic capsule due to alpha-1 blockade

• decrease respiratory rate
• (low doses) tidal volume increases

• 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)

antiemetic

it has antihistamine effects

analgesic (may enhance analgesic effects of other drugs)

causes penile prolapse (usually temporary- good for cleaning sheath)--> may become persistent- paraphimosis

Acepromazine

Azaperone (Stresnil)- used as an aid in mixing and sorting

• minimal tranquilization/ less potent in animals than people
• mild calming in older animals
• can produce dysphoria
• muscle relaxation
• effects are supra-additivewwith general anesthetics

• Diazepam (Valium)
• Midazolam (Versed)
• Zolazepam (Telazol)
• Lorazepam (Ativan)

• 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

• 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]

• depression of myocardial activity
• hypotension
• bradycardia
• cardiac arrhythmias

• 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

does not mix in same syringe with other drugs (except ketamine)

• 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)

• 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

• more potent and longer-lasting that diazepam
• one of two drugs contained in telazol

• good muscle relaxation
• analgesia
• useful in feral cats and pigs for general anesthesia

• telazol, ketamine, xylazine
• telazol can cause prolonged and unpredictable recoveries
• telazol is not reversible

Flumazenil (Romazicon)

orally in cats prior to travelling

• sedation
• muscle relaxation
• analgesia

• xylazine (horses, dog, cats, deer)
• detomidine (horses)
• dexmedetomidine (dogs, cats)
• romifidine (horses)

• 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

• peripheral vasoconstriction 
• hypertension 
• [due to extrasynaptic vascular alpha-2 receptor stimulation and some small degree of alpha-1 stimulation]
• pale MMs

• 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

shorter; longer

• respiratory depression (respiratory center sensitivity to CO is decreased)
• decreased resp rate
• increased tidal volume (P_aCO₂ and P_aO₂ 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)

• 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

Xylazine

• inhibit tubular reabsorption of sodium
• produce diuresis

rapid absorption after IM, SQ, and IV injection

severe bradycardia and bradyarrhythmias, vomiting, profound sedation.

sedation, muscle relaxation, treating colic pain, "head down posture", caudal epidural anesthesia

• 100x more potent than in horses or dogs
• produced oxytocin-like response (premature parturition in near term cows, milk let down)

more potent and longer-lasting

antisedan, yohimbine, tolazine, doxapram, atipamezole

IM (can cause hypotension and excitement if given too rapidly IV)