Injectable Anesthetics Flashcards
Pros of injectable anesthetics
Rapid onset of anesthesia Rapid control of airway IM injection possible Minimal equipment
Cons of injectable anesthetics
Minimal conrol over waking Controlled substances
Injectable anesthetics
Barbiturates Propofol Alphaxalone Dissociative agents Etomidate
Types of barbiturates
Thiobarbiturates Oxybarbiturates
Thiobarbiturates
Thiopental (III) Ultrashort acting 20 minutes
Oxybarbiturates (type & how long lasts)
Phenobarbital (IV) -~12hours Pentobarbital (II) - ~1-2 hours Methohexital (IV) - ~20 mins
Barbiturate mechanism of action
GABA, GA?, BDZ , Cloride channel (**PICTURE**)
Barbiturate Pharmacologic effects on CNS
Dose-dependent CNS depression Decreased intracranial pressure (except methohexital)
Barbiturate Dose-dependent CNS depression
Sedation Hypnosis Anesthesia Coma Death
Barbiturate Pharmacologic effects on Respiratory system
Dose-dependent respiratory depression Oral administration has minimal respiratory effects
Barbiturate Dose-dependent respiratory depression
Transient apnea Intubate & assist with breathing as necessary Cats more sensitive than other species
What species are more sensitive to respiratory depression by barbiturates?
Cats! Meow
Barbiturates Pharmacologic effects on CV system
Hypotension Myocardial sensitization to catecholamines
Barbiturates - Hypotension
Decreased stroke volume & cardiac contractility Vasodilation Reflex tachycardia
Barbiturates - Myocardial sensitization to catecholamines
Arrhythmias Vagal stimulation
Barbiturates - Pharm. effects on skeletal system
Decreased motor end-plate sensitivity to ACh -Incomplete relaxation of abdominal muscles -Laryngeal reflexes preserved
Barbiturates - Pharm. effects on Body Temperature
Hypothermia due to peripheral vasodilation and decreased basal metabolic rate
Barbiturates - Pharm. effects on renal system
Hypotension –> reduction in GFR can lead to oliguria Stimulation of ADH
Barbiturates - Pharm effects on Reproductive system
Depression of uterine contractions & fetal respiration
Barbiturates - Administration
Given IV (usually 1/3 to 1/2 the dose as a bolus)
Phenobarbital Administration
For sedation & anticonvulsive Orally PO bioavailability of 90%
Barbiturates - Distribution
Widely distributed to all tissues, including CNS *Very Lipid-soluble* Protein binding variable
Barbiturates - Redistribution
Can be seen Animal wakes up before drug is metabolized (adipose depot)
Barbiturates - Distribution Effect of systemic acidosis
Systemic acidosis may increase distribution
Barbiturates - Protein binding
Thio >70% Pento ~45%
Barbiturate - Metabolism @Liver
Hydroxylation in the liver
Barbiturate - Metabolism @Kidney & Brain
Inactivation
Barbiturate metabolism in greyhounds
Exhibit prolonged effect Deficient in oxidative enzymes for metabolism
What is the biggest hepatic microsomal enzyme inducer?
Phenobarbital, used long term
Barbiturate - Excretion
Renal excretion Increased by alkalinization of urine
What increased barbiturate excretion?
Alkalinization of urine
Barbiturate - Clinical uses
Sedation Induction of general anesthesia Treating CNS excitatory toxicants Anticonvulsants Euthanasia
Barbiturates in sedation
Phenobarbital - oral
Barbiturate for induction of general anesthesia
Thiopental (IV)
Barbiturate for treating CNS excitatory toxicants
Phenobarbital, pentobarbital (IV)
Barbiturate for anticonvulsant, prevention & treatment
Phenobarbital (Oral, IV)
Barbiturate for euthanasia
Pentobarbital (IV)
Barbiturate - Adverse effects
Respiratory depression (post-induction apnea) Cardiac depression/ hypotension Cardiac arrhythmias (esp. thiobarbiturates) Splenic enlargement (RBC sequestration) Long recovery Hyperalgesia (at sub-anesthetic doses) NOT analgesic
Barbiturate cautions - pre-existing conditions
Caution with: Cardiac disease, hypotension, shock Liver or Kidney disease Hypoproteinemia
Barbiturate caution- Mode of administration
Do not give IM/SC/Perivascular/Intraarterial Causes tissue damage
Barbiturate caution in “topping up”
Redistribution
Better options than barbiturates are recommended for these animals:
Greyhounds & sighthounds Pregnant animals Splenectomy
Barbiturate - drug interactions
CNS depressants Muscle relaxants Chloramphenicol - may prolong barbiturate
Thiopental (Pentothal) Pros
Reliable, inexpensive
Thiopental (Pentothal) Species doses: Horse, Dog, Cat
Horse: 10% solution, pH 12 Dog: 2.5% solution, pH 11 Cats: 1.25% solution, pH 9.5
Thiopental (Pentothal) Lasts how long?
Ultra-short acting - ~20mins
Thiopental (Pentothal) Shelf life?
Short shelf life once reconstituted
Thiopental (Pentothal) Wide/Narrow therapeutic index
Narrow therapeutic index
Thiopental (Pentothal) Lipid soluble?
Very highly lipophilic Redistribution can be significant
What does this picture depict?
Redistribution with thiopental
Methohexital (Brevital) Former use
Formerly for IV induction in greyhounds (now other agents used)
Methohexital (Brevital) Effect time
Ultra-short acting (~10mins)
Methohexital (Brevital) Actions
Excitement on induction and recovery
Methohexital (Brevital) Effects on respiratory system
Significant respiratory depression
Pentobarbital Use
(Nembutal, Euthasol) Usually only for euthanasia
Pentobarbital Administration
Can be used for IV induction in sheep/goats -Metabolize it faster than other species
Pentobarbital Effect time
Short acting 1-2 hours
Pentobarbital When is it used for long-term sedation?
In treatement of CNS excitatory toxicants ex- Metaldehyde poisoning
Propofol Two sub-types
Propoflo Propoflo 28
Propoflo Similar to what drug? How do they differ?
Similar to thiopental -Less hangover, faster induction/recovery