Inhalant General Anesthetics Flashcards
Nitrous oxide does not cause unconsciousness… why is it used?
Excellent analgesic and alleviates anxiety; can also reduce amount of hydrocarbon anesthetic needed
all inhalant anesthetics by the early 1950s had at least one of what two major drawbacks
1) explosive when administered with oxygen
2) produce toxic metabolites
how do we reduce the flammability of a hydrocarbon
by substituting their hydrogen for a halogen
halothane-oxygen mixtures are explosive/non-explosive
non-explosive
in general, hepatic and renal toxicity are directly related to the extent at which an inhalant is
metablolized
what are the main inhalants used in veterinary medicine today
- isoflurane
- sevoflurane
the TI of all hydrocarbons ranges from
2-4
why do we not use newer inhalant anesthetics?
they offer little or no advantage over iso or have serious drawbacks
To be both safe and effective, general anesthetics must (2)
inhibit cerebrocortical activity while maintaining brainstem function
the safety of general anesthetics is dependent on
the extent to which CVS and respiratory functions are impaired at concentrations required to maintain unconsciousness
what is the MOA of inhalant anesthetics
not fully understood, but involves GABA facilitation
how is inhalant anesthetic absorbed and eliminated
absorbed into blood from lungs; eliminated mainly be exhalation
depth of anesthesia is proportional to:
partial pressure of the anesthetic
what is partial pressure
the physical pressure exerted by one gas (in a mixture of gases) within a container
how do highly soluble gases influence partial pressure and overall effect
highly soluble -> move slowly in tissues (because they form bonds) -> weak partial pressure and weak effect
how fast do highly soluble gases get absorbed and eliminated
absorbed quickly; eliminated slowly
rate of onset and recovery depends on
partial pressure
how do poorly soluble gases influence partial pressure and overall effect
move rapidly in tissues -> high partial pressure -> high overall effect
how fast do poorly soluble gases get absorbed and eliminated
slowly absorbed; quickly eliminated
will a high or low soluble anesthetic render a patient unconscious more quickly (assuming a high concentration gradient to force the anesthetic into the tissue)
low soluble (because it has a higher partial pressure)
will a patient recover more quickly if given an anesthetic with high or low solubility
low
how do we overcome the problem of getting a poorly soluble inhalant anesthetic drug into the body
by creating a high concentration gradient between the capillaries and alveoli
what is the blood gas parturition coefficient
the relative solubility of drug in tissues vs alvgeolar gas
what is the BGPC for:
- sevoflurane
- isoflurane
sevoflurane: 0.68
isoflurane: 1.4
how can we determine the concentration of anesthetic that is present in the brain
multiply the concentration of inhalant anesthetic being delivered by the BGPC
the BGPC for isoflurane is 1.4, what does this mean?
the concentration of iso in the tissues is 1.4x the concentration in the alveolar air
or
if you administer 1% iso, the concentration in tissues is 1.4%
the onset of unconsciousness and recovery are fast with __________ drugs and slow with __________ drugs
poorly-soluble; highly-soluble
how do we utilize the concentration of anesthetic in the inspired air to induce a patient more quickly
can increase (so more enters tissue with each breath) and then decrease once the patient is unconscious
T/F we can control the inspired anesthetic concentration using a precision vaporizer
T
how does ventilation rate impact the concentration of anesthetic in the brain
the faster the patient breathes, the faster the anesthetic is delivered to and absorbed from the lungs
what are 2 factors that influence inhalant anesthetic delivery to the brain that we cannot readily control
1) pulmonary blood flow
2) pulmonary/venous concentration gradient
what are 3 factors that influence drug delivery to the brain that we can readily control
1) BGPC
2) concentration of anesthetic in the inspired air
3) ventilation rate
inhalant anesthetics are eliminated mainly by
exhalation
what are 3 factors that influence the elimination of an inhalant anesthetic
1) solubility in tissues
2) respiratory rate
3) pulmonary blood flow
what effect do inhalant anesthetics have on thermoregulation
depress -> cause some degree of hypothermia
halothane has ~25-40% metabolism, isoflurane has ~0.2% metabolism and sevoflurane has ~3-5% metabolism
place the drugs in order of most to least toxic
halothane, sevoflurane, isoflurane
metabolites of inhalant anesthetic metabolism are usually damage to what organs
liver and kidney
what are 3 harmful metabolites of inhalant anesthetics
1) trifluoroacetic acid
2) Br-
3) Cl-
what is used to compare potency of inhalant anesthetics
MAC
what is MAC50
concentration of anesthetic in the inspired air that will prevent 50% of patients from feeling a painful stimulus
the MAC for very potent drugs would be relatively (high/low)
low
what is used to control the vaporizer setting
MAC50
The MAC95 value is about _____% higher than MAC50, so in unpremedicated patients you should set the vaporizer at ____x MAC to start, then adjust
30-40%; 1.3x
what do we set the vaporizer to in premedicated patients to start
MAC50 value
lines in what species are susceptible to malignant hyperthermia
pigs, dogs and humans
malignant hyperthermia is caused by mutations in the
skeletal muscle calcium release channel (RYR)
what happens to mutated calcium release channels when exposed to halogenated hydrocarbons
uncontrolled muscle contraction
how do we treat malignant hyperthermia
dantrolene
why is it important to change out soda lime regularly when using iso as the inhalant anesthetic
it forms CO when exposed to desiccated CO2 absorbents
what is a drawback of iso that is only important when the patient is not being stimulated
dose-dependent drop in blood pressure
what is isoflurane’s only real drawback
pungent odour
is it better to use isoflurane or sevoflurane on reptiles and amphibians
sevoflurane (because they can hold their breath for over 20 min)
what happens to sevoflurane when exposed to CO2 absorbents
releases Compound A, which is nephrotoxic
