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63 Cards in this Set

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what is vapor pressure?
the pressure exerted by vapor moleucles once in equilibrium with liquid
how does vapor pressure affect anesthetics?
gases/vapors can be administered in a range (0-100%), the greater the vapor pressure the greater concentration possible, vapor pressure is compared to atmospheric pressure at sea level (760 mmHg)
if the vapor pressure of methoxyflurane is 28mmHg, what is the concentration?
28/760 = ~3%max
if the vapor concentration of isoflurane is 32%max, what is the vapor pressure?
760 x .32 = 240
what is vapor pressure dependent on?
temperature; increased temperature = increased vapor pressure and increased potential inhalent concentration
what does a vaporizer do?
dilutes vapor with O2 and/or N2O, permits the administration of gases in clinically relevant concentrations, are agent specfic and color coded
how is the % anesthetic calculated?
flow from vaporizer chamber/total gas flow
what is solubility?
the extent gas/vapor dissolves in solvent (ie how much ISO dissolves into blood, fat, tissue)
what is solubility dependent on?
chemical nature of gas, partial pressure of gas, nature of solvent, temperature
what is meants by fully saturated?
gas is in all layers (ie gas, oil, water), but gas numbers will vary
how does solubility affect induction?
the more soluble the gas, the more uptake, the longer it takes to become saturated = slower induction
how does solubility affect recovery?
the more soluble the gas, the longer it takes to be removed from the body, slower recovery
what does MAC stand for?
minimum alveolar concentration of anesthetic
what is MAC?
minimum alveolar concentration of anesthetic that renders 50% healthy non-premedicated subjects non reactive to noxious stimuli (remember, 50% do move, the MAC of ISO in dogs is ~1.3%)
what does MAC allow?
comparisons between different inhalents, estimation of where to set vaporizer
what happens to MAC values if anesthetics are combined?
MAC values are additive
What increases MAC?
hyperthermia, CNS stimulation (excitement, drugs, disease)
what decreases MAC?
age, hypothermia (nost anesthetized patients get cold), other CNS drugs/depressants/analgesics (opioids, alpha-2 agonists, acepromazine), pregnancy, concurrent disease
what are the historic anesthetic inhalents?
ether, chloroform, methoxyflurane
what are the present anesthetic inhalents?
halothane?, isoflurane, sevoflurane, nitrous oxide (N2O)
what are the possible future anesthetic inhalaents?
desflurane, xenon?
what is an unusual feature of MACs?
relatively conserved across species
what is surgical MAC (MACsx)
1.3 to 1.5 times MAC, 95% of patients will remain asleep and allows estimation of vaporizer setting
what would you set the ISO vaporizer at for surgery on a dog premedicated with acepromazine?
MAC of ISO in dog is ~1.3%, 1.3% x 1.5 (surgical) = 1.95%, 1.95 x 0.50% (decrease from acepromazine) = ~1%
what is ether, chemically?
diethyl ether
what are the advantages of ether?
cheap, good skeletal muscle relaxation, minimal cardiovascular depression
what are the disadvantages of ether?
expolosive, very slow and unpleasant induction, prolonged recovery, respiratory irritation
what are advantages of methoxyflurane?
nonflammable, non-explosive, mild cardiovascular depression, non-irritating to respiratory tract
what are disadvantages of methoxyflurane?
vapor concentration is limited to a maximum of 3.0%, very soluble so induction takes 20-30 min and recovery is prolonged, renal toxicity (flouride ion metabolite produced in the liver)
what are the features of halothane?
nonflammable, non-explosive, less soluble than methoxyflurane resulting in 7-10min induction and 5-15min recovery, potent myocardial depressant, sensitizes heart to catecholamines, does not irritate mucous membranes of respiratory tract but does cause respiratory depression, ~25% is metabolized by the liver and hepatitis has been diagnosed 2-5 days following anesthesia
what are the features of isoflurane?
less soluble than halothane so rapid induction and recovery ~5min, dose dependent vasodilation but less myocardial depression than halothane and does not sensitive myocardium to catecholamines, respiratory depression and irritating ot mucous membranes of respiratory tract, almost no liver metabolism (~0.2% metabolized)
what are the features of sevoflurane?
less soluble than isoflurane for rapid onset and recovery, dose dependent vasodilation (similar to ISO) and does not sensitize the myocardium to catecholamines, dose dependent respiratory depression but non-irritation, ~3.0% metabolized by liver
what are the features of desflurane?
minimal solubility so very rapid onset and recovery but the high vapor pressure necessitates special vaporizer (expensively specialized and requires power supply, does cause airway irritation, but has minimal liver metabolism (0.02%)
what are the features of nitrous oxide (N2O)?
unique analgesic inhalent, can cause increased sympathetic stimulation, incomplete anesthetic in animals, administered in very high concentartions (~67%; the MAC is ~200% in animals therefore oxygen is delivered in smaller percentages), N2O diffuses 37x faster than nitrogen and is tetragenic when used in first trimester, contraindicated with any gas filled disease (GDV, pneumothorax) and hypoxemia/pulmonary disease
what do we consider when choosing an inhalent?
safety in terms of cardiovascular, respiratory, metabolism, CNS effects, pleasant induction/recovery, cost
what inhalents decrease blood pressure?
isoflurane, halothane, sevoflurane
what inhalent causes myocardial depression?
halothane
what inhalent causes vasodilation?
isoflurane and sevoflurane
what inhalent can cause arrhythmias (sensitizes heart to catecholamines)?
halothane
what should we avoid halothane with?
myocardial depression, arrhythmias, catecholamine release (pheochromocytoma)
which is more cardiovascularly safe, SEVO or ISO?
neither
what are the respiratory effects of all inhalents?
decrease minute ventilation resulting in hypercapnia, alter responses to hypoxia and hypercapnia but there are species differences between inhalent and respiratory depression (apneic index)
what inhalent is a bronchodilator and good for asthmatics?
halothane
what is the apneic index?
% inhalent when apneic/MAC of inhalent. The higher the number the better the ventilation
caution must be taken with all inhalents in patients with what?
pulmonary disease/hypoxemia, obesity/respiratory muscle weakness, high intracranial pressure (increased CO2 will further increase ICP), may need ot assist or control ventilation
how is an ideal inhalent metabolized?
it's not, rather it is exhaled from body
what inhalent should be avoided in animals with liver disease or dysfunciton?
halothane (~25% metabolized), might avoid SEVO as well (3% metabolized)
what is the CNS effect that all inhalents have?
decrease cerebral autoregulation in a dose depenent manner (ISO less than HALO)
what inhalent do we use in patients where we want to preserve cerebral autoregulation (high intracranial pressure, craniotomies)?
Isoflurane (in smallest amount possible, but may want to avoid inhalents completely)
what inhalent gives us the most rapid induction/recovery?
Sevoflurane is least soluble, so quickest
what inhalent is irritating to the airway and unpleasant to smell?
Isoflurane
what inhalent is non-irritation to the airway and pleasant smell?
sevoflurane
what inhalent do we use for mask inductions?
Sevoflurane (less irritating/fighting)
what inhalent do we use for exotics/neonates (where quick recovery is important)?
Sevoflurane
rank in order of least to most cost: halothane, isoflurane, sevoflurane?
halothane ($0.10), isoflurane ($0.28), sevoflurane ($0.88)?
why would we care about inhalent cost?
profit, client affordability, patient care
how much waste gas exposure is recommended for inhalents and N2O?
inhalents < 2ppm, N2O < 25 ppm
When can we smell inhalents?
~50ppm
where does exposure to waste inhalents occur?
leaky machine, poor cuff, from patient during and after extubation
what are the risks and concerns about waste inhalents?
risks are unknown, but veterinary careers are long, be careful
if we want a quick recovery from gas anesthesia, we want to use what kind of inhalent?
insoluble inhalent
what is the target organ for inhalents?
CNS
what term describes inhalents?
anesthetics