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What are the characteristics of an ideal injectable anesthetic?
- Rapid onset and recovery
- Lack of tissue toxicity
- Lack of adverse cardiovascular and repiratory effects
- Rapid metabolism, even if deficient liver and kidney function
- Provide analgesia
- Provide skeletal muscle relaxation
What are the barbiturates used for?
- general anesthesia
- anticonvulsants and euthanasia
- mostly commonly used as induction agents prior to intubation
What are the respiratory depressant of the barbiturates?
- Brief apnea common after induction
- Barbiturates cross placenta, may depress respiration in the neonate
What are the cardiac effects of the barbiturates?
- Dose dependent decrease in CO and BP
- Thiopental increase heart's sensitivity to epinephrine wich can cause premature ventricular contractions, may see bigeminy (one normal wave and one ventricular wave)
- Can also see tachycardiac, bradycardiac or AV heart block due to ANS imbalance
- Use in caution in animals with known cardiac disease
Why shouldn't barbituates be use in hypoproteinemic animals?
Increased levels of free drug (crosses into brain) versus protein bound drug (unable to cross into brain).
Why shouldn't barbituates be used in acidotic animals?
Barbituates have increased potency when in acidotic environment.
Why shouldn't thiopental or pentobarbital in sighthounds be used? (barbituates)
- Due to lack of drug distribution into body fat
- Also due to decteased hepatic metabolism
Why shouldn't barbituates be used in shock patients?
Blood flow to fat tissue decreased, increased blood flow to brain and heart
Are barbituates a controlled substances? (tiopental and pentobarbital)
Which drugs is sometimes called intermediate-acting AKA short acting?
What is the duration of pentobarbital and what is it use to treat?
- Duration of action is 30 min - 2hrs
- It treat status epilepticus
- Slowest action of the barbiturates
- Rough (paddling and thrashing) prolonged recovery, which may take hours to days
- Termination of effects caused by hepatic metabolism
- Low lipid solubility
- Most commonly used as anticonvulsant or agent now.
What are the ultra short acting barbiturates?
- Thiopental (pentothal)
- Methylated oxybarbiturates- methohexital (brevital)
What is the duration of action of Thiopental and the onset of action?
- Duration: 10-20mins
- onset: 30-60sec
Why is Thiopental not good to use in sighthounds and thin athletic dogs?
- High lipid slubility
- Recovery occurs as drug is redistributed to muscle and fat, followed by excretion via hepatic metabolism.
- Recovery may be prolonged in sighthounds and thin athletic dogs.
- Complete recovery usually takes 1-2hrs
- Supplied as a crystalline powder in multidose vials for reconstitution. No bacteriostatic agent present use caution when reconstituting
- Strongly alkaline solution can cause severe tissue damage if injected perivascularly. Use IV catheter. If perivascular injection occurs infiltrate with equal volume of saline +/- 2% lidocaine (can kill the tissue)
- Usually bolus 1/3-1/2 initial dose over 10-15 sec. the titrate slowly to effect.
- Debilitated animals may only require 80% of the calcualted dose
- Don't use on hypoproteinemic or acidotic animals
- Thiobarbiturates decrease intracranial and tnreocular pressure
- Causes splenic engorgemnetconseder sugical prcedure, diagnostic test.( in case in need of explaratory)
What is the duration of action and onset of action of Methylated oxybarbiturates?
- More rapidly metabolixed than Thiopental recovery with 30 minutes
- Can be used in sight hounds
- Comes as powder, reconstitue to 1% solution 6wk shelf life
- Less irritaiting than thiopental if injected perivascularly
- Associated with excitement in recovery especially if used alone. Recommend premedication with a sedativie or tranquilizer
- May see seizures in induction or recovery use diazepan to control
- Don't use in animals with pre-existing CNS disease
What drugs are in the cyclohexamines family?
What does cycloheximines do?
Disrupt nerve condition with in the cerebrum, causing selective CNS stimulation
What are the contraindications of cycloheximines?
patients with seizures disorders
What do you see with the use of cyclohexamines, which are ketamine, Phencyclidine, Tiletamine?
- Exaggerated reflexes- brisk palpebral, pedal and corneal
- Persistence of pharyngeal and laryngeal reflexes (weak)
- Marked sensitivity to sound, light and sensory stimuli, especially in recovery.
- Muscle tone increased, sometimes rigid
- May see apneustic respiration-insipiration followed by a prolonged pause and short expiration
Does cyclohexamines depress cardiac reat or function?
- No, see increased heart rate, myocardial function and blood pressure due to release of epinephrine
- Use in caution if pre-existing arryhthmias or cardiac disease.
Are cyclohexamines good analgesia?
No, because it only gives analgesia to the skin and limbs not to visceral.
- Eliminated by metabolism in liver, or by renal excretion-renal excretion-specie dependent
- Eyes remain open, pupil remains central and dilated, nystagmus may occur
- May cause increased salivation and lacrimation
- Irritating on injection (IM, Perivascular) can give IM or IV
- May increase CSF pressure-contraindicated in head trauma
- Licensed for use in cats, also used in dogs, birds, horses, and exotics
- Excreted primarily through kidney in cats, liver in dogs
- Schedule III Controlled substance- Records, logs
What is the onset of action and recovery for ketamine?
- Onset: 90 sec when given IV
- Recovery usually occurs with 2-6hrs
Why do dogs recover more quickly than cats with Ketamine?
Because dogs metabolize it in the liver
Why would you combine Ketamine with a tranquilezer?
To aid muscle relaxation and prevent excitement during recovery
Very popular in cats and dogs. Minimal cardiac depression, good muscle relaxation, superior recovery, less risk of seizure, some analgesia. Can also use Ketamine-Midazolam
Most frequently used in equine anesthesia
May see bradycardia, heart block, seizures in recovery
Used in cats less muscle relaxation
- Only availabe with zolazepam in the drug telazol
- Sold as a powder which must be reconstituted
- Schedule III controlled substance
- Causes less apneustic respiration then ketamine
- Telazol may be used IV, IM, SQ
- Also used in wildlife
- Disadvantage is long, difficult recoveries
What is a neuroleptanalgesia?
Not a method of anesthesia but a state of calmness with some dissociation from the environmetn; analgesia; and lack of aggressiveness
What is neuroleptanalgesia made?
Its a combination of opiodand tranquilizing agent, frequently mixed in same syringe except for diazepam
Give examples of neuroleptanalgesia
- Morphine and Acepromazine
- Oxymorphone and Acepromazine
- Butorphanol and Acepromazine
What are neuroleptanalgesia used for?
Can be used for sedation, or for induction of anesthesia
- Nonbarbiturate, non dissociative, intravenous anesthetic agent which is ultra-short acting
- Used for short procedures or anesthetic induction, also control of status epiepticus
- Oil in water emulsion with a milky apperance- safe IV
- Expensive, preservative presnt-Use strict aseptic technique currently 28 days shelf life
- No analgesic effect
- Safe for use in sighthounds
What is the onset and duration of propofol?
How does propofol redistributes?
- Redistibutes from brain to muscle and fat, but metabolized 5-10times faster than thiopental.
- Can be repeated as needed to maintain anesthesia, or give infusion
What are the adverse effects of propofol?
- Respiratory deppression- see apnea if injected rapidly IV
- Cardiac depressant-Bradycardia, decreased cardiac output.
- Frequently see hypotension immediately after induction. Don't use if patient is hypotensive in shock, dehydrated or anemic
What drug can be use in patients of liver or kidney disease?
What can you see when propofol is use?
May see paddling, muscle twitching, nystagmus, opisthotonus posture- tx with diazepam if necessary
What kind of drug is Etomidate?
What drug is good if patient is in shock and why?
- Etomidate because it has minimal effect on cardiovascular function
- Not supported on study done in greyhounds where bradycardia, hypotension and PVC's were supported
What drugs can cause apnea?
Why is etomidate not popular?
- Rapid injection may cause hemolysis in cats
- Suppresses adrenocortical function-don't use in patient with Addison's disease
- Nausea, vomiting, sneezing, and myoclonic twitching may be seen on induction
- No preservative onpen vials should be discarded
- New, not in US yet
- Similar to propofol but less adverse cardiovascular effects
- Can be used IV or IM (w/midazolam)