General Veterinary Anesthesia

Joanna Webb
CHEM 5398
Spring 2010
History of Anesthesia
Methods of Administration
Mechanisms of Action
Companion Animal Drugs
• Amnesia
– Loss of memory
• Immobility
– Stay still
• Analgesia
– Pain relief
• Homeostasis
Blaze ppt. TCSVM
Less Common:
• Used to think all anesthetics worked the same
• The gas disrupted cell membrane lipids
• Flaw: enantiomers of the same anesthetic
have unique actions but the same physical
properties (i.e. isoflurane)
• Therefore, anesthetics must bind to specific
• Hyperpolarize neurons
• Anticholingeric: suppresses nervous system
• Alpha-2 adrenergic receptor
agonist/antagonist: suppress norepinephrine
binding/release to receptor
• Cardiovascular depressant
• Respiratory depressant
•Ach is a main neurotransmitter of
the autonomic NS of PNS
•In the CNS, excitatory actions
• Diethyl ether, nitrous
oxide, chloroform
• Halothane
• Isoflurane
• Sevoflurane
First anesthetic discovered
Nontoxic to organs
Unpleasant smell
Decreases possibility of action potential by
decreasing rate of rise to an end-plate
• Colorless and odorless
• Hepatotoxin
• Severe CV depressant
– Cardiac arrhythemia
– Aka Sudden Sniffer’s
• Blocks flow of K+ out of
the cell
• Binds to GABA receptor:
enhances inhibitory synapses
– Lets more Cl- into the cell
• Competitive glycine inhibitor:
agonist for N-methyl-Daspartic acid (NMDA) receptor
• Pre-medicate with a
• Dog: 2.0-2.5% isoflurane
concentration (in oxygen)
• Horse: 3.0-5.0% isoflurane
concentration (in oxygen)
• Can keep it on a low
concentration throughout the
Newer, more expensive than isoflurane
Dogs: Induce with 7.0% sevoflurane
Maintenance level is 3.3-3.6% with pre-medication
3.7-4.0% maintenance concentration without premedication
• Common pre-meds: benzodiazepine or phenothiazine
• Isoflurane is safer because patient does not require as
much anesthesia, can be kept lighter
– Higher cardiovascular stability
• Mild sedative, analgesic
• Acepromazine
– Combine with NSAID or opiod
• Medetomidine
• Atipamezole
Induction anesthetics
• Dissociative
– Ketamine
– Tiletamine
• Benzodiazepines
– Diazepam
– Zolazepam
• Propofol
• Barbiturates
• Partition into the highly lipophilic tissues of
the brain and spinal cord
• Produce rapid anesthesia
• Immediate low concentrations of anesthetic in
blood stream causes the drug to leave the CNS
and enter the peripheral tissues via the blood
• Effect can wear off in about 10 minutes unless
continuously infused
Ace is provides strong sedation and antiemetic effects
Give with a NSAID or opiod to provide anagesic effects
6-8 hours of activity
Anticholinergic, antihistamine, antispasmodic, and
alpha-andrenergic blocking
• Medetomidine is an NSAID
– Strong sedative, strong analgesic
– Alpha-2 adrenergic receptor agonist
– 45-90 minutes
• Atipamezole
– Reversal agent
– Alpha-2 adrenergic receptor antagonist
– Administer a new analgesic after reversal since ALL effects of
medetomidine are reversed
• Ketamine inhibits excitatory
S (+)
– Dissociate: cataleptic state
– Eyes open, limb movements
• Serotonin, dopamine
– High analgesic effects
– Hypnotic state
• Increases intracranial pressure
and blood flow
• Marketed as a racemic mixture
• Partially water soluble pKa 7.5
• Highly lipophilic
R (-)
• Alpha-2 andrenergic
receptor agonist
• Binds to GABA receptor
– Gamma-aminobutyric acid
>20%: anxiolysis
>30-50%: sedation
>50%: unconsciousness
• Opens Cl- channel,
hyperpolarize membrane,
so inhibitory
• Given with ketamine to
produce better anesthetic
• Pentobarbital
• Derivative of barbituric acid (has no CNS activity)
– Oxygen or sulfur at 2 position
– Adds to CNS depressant activity
• Commonly used in rats: research
• Marketed as pentobarbital sodium powder
– Soluble in water or alcohol, forms clear solution
• Inhibits excitatory and enhances inhibitory CNS
Barbituric acid
Blaze, C.A. (2009). Veterinary anesthesia and analgesia introduction. Microsoft Powerpoint. Tufts
Cummings School of Veterinary Medicine.
Chloroform. 2010). Wikipedia. Retrieved (2010, April 4) from
Dickinson, R, Peterson, B.K, Banks, P.B., Similis, C, Martiin, J.C.S., Valenzulela, C.A., Maze, M, Franks,
N.P. (2007). Competitive inhibition at the glycine site of the N-methyl-D-aspartate receptor by the
anesthetics xenon and isoflurane: evidence from molecular modeling and electrophysiology.
Anesthesiology, 107(5): 756-767.
Muir, W.W. (2008): Intravenous anesthetic drugs: dissociative anesthetics. DVM360. Retrieved
(2010, April 5)
End plate potentials. (2009). Wikipedia. Retrieved (2010, April 4) from
University of Minnesota. Guidelines for the use of anesthetics, analgesics and tranquilizers in
laboratory animals. Accessed 15 February 2010. <>
• Goodman and Gilman’s Pharmacological Basis
of Therapeutics, Chapter 13, pp. 341-363
• Draw the structure of propofol, the most commonly used
anesthetic in the US.
• Propofol is not water soluble, thus has to be constituted in an
emulsion-like mixture of soybean oil, glycerol, and egg phosphatide.
Circle the structural features responsible for its water insolubility.
• Halothane, isoflurane and sevoflurane are commonly used
inhalation anesthetics. Draw their structures
• Draw and label the R and S stereoisomers of ketamine.
• Which stereoisomer of ketamine has more psychic emergence?
Which stereoisomer contributes more analgesic and anesthetic
• Thiopental (pentobarbital), thiamylal, methohexital are all
derivatives of barbituric acid. Draw their structures and that of the
parent structure barbituric acid.