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94 Cards in this Set

  • Front
  • Back
what general anesthetic is a gas?
nitrous oxide
isoflurane
general anesthetic (volatile liquid)
desflurane
general anesthetic (volatile liquid)
sevoflurane
general anesthetic (volatile liquid)
stage I of anesthesia
"analgesia"

- analgesia
- amnesia
- euphoria
stage II of anesthesia
"Excitement"

- excitement
- delirium
- combative behavior
**like a bad nightmare**
stage III of anesthesia
"Surgical Anesthesia"

- unconsciousness
- regular respiration
- decreasing eye movement
stage IV of anesthesia
"Medullary Depression" = OD

- respiratory arrest
- cardiac depression and arrest
- no eye movement
list the stages of anesthesia experienced by a patient as they are being put under for and then awakening from a surgery
Stage I: Analgesia
Stage II: Excitement
Stage III: Surgical Anesthesia
surgery performed and anesthetic stopped
Stage II: Excitement
Stage I: Analgesia
definition of general anesthetic
drug which causes analgesia, amnesia, loss of consciousness, inhibition of sensory and autonomic reflexes, and skeletal muscle relaxation
why is it important that general anesthetics inhibit autonomic reflexes?
prevents the patient's blood pressure and heart rate from changing when an incision is made
what is the advantage to quick induction with general anesthetics?
with fast induction, the patient passes rapidly through the undesirable "excitement" phase (stage II) of anesthesia
define induction, as it pertains to anesthesia
rate of onset of anesthesia

(how quickly alveolar partial pressure of an anesthetic equilibrates with inspired partial pressure of the anesthetic)

**initially, the inspired partial pressure is much greater than the alveolar partial pressure**
define maintenance of anesthesia
maintaining constant alveolar partial pressure of anesthetic at therapeutic levels

**during maintenance, inspired partial pressure of the anesthetic will be equal to the alveolar partial pressure of that anesthetic**
define recovery from anesthesia
rate of decline of alveolar partial pressure of an anesthetic

**when a surgery is finished and a patient is being weaned from anesthesia, the alveolar partial pressure must decrease from therapeutic levels to zero**
define partial pressure
the partial pressure of a gas in a mixture of gases is the portion of the total pressure (760 mmHg) that is supplied by a particular gas
why are neuromuscular blocking drugs often used in addition to anesthetics?
often used to cause flaccidity of muscle, which enables the anesthesiologist to decrease the dose of general anesthetic required

**especially useful when working in highly muscular areas, like the abdominal cavity**
what is the main difference between a low-flow anesthetic machine and a high-flow anesthetic machine?
a low-flow system has a carbon dioxide absorber, whereas the high-flow system doesn't
blood/gas partition coefficient
ratio describing distribution of a gas between two phases (gas and blood) at equilibrium; i.e. ratio of gas dissolved in a given volume of solvent to the amount of free gas that would occupy the same volume of space

determines the rate of induction
what inactive reservoir must be saturated before anesthetic equilibrium can be achieved?
proteins in the blood

lipophilicity determines how quickly alveolar partial pressure equilibrates with arterial partial pressure of an anesthetic, b/c lipophilic anesthetics must bind to proteins and fill this reservoir before the partial pressure of the anesthetic in the blood can equilibrate with its partial pressure in the alveoli
what are the three main categories of anesthetics classified based on blood solubility?
soluble - high (double-digit) blood/gas partition coefficient - slow induction rate

intermediate - single-digit blood/gas partition coefficient - intermediate induction rate

poorly soluble - blood/gas partition coefficient of about 0.5 - rapid rate of induction
what anesthetic is in the intermediate solubility classification of anesthetics?
isoflurane

blood/gas partition coefficient of 1.4

intermediate rate of induction
what anesthetics are in the poorly soluble classification of anesthetics?
anesthetic (blood/gas partition coefficient)
nitrous oxide (0.47)
desflurane (0.45)
sevoflurane (0.65)

poorly soluble, therefore rate of induction is very rapid
what is indicated by a high blood/gas partition coefficient? what does this mean for general anesthetics?
high lipophilicity

because of high lipophilicity, the general anesthetics will seek out lipophilic portions of the blood (e.g. proteins)
what is the active fraction of an inhaled anesthetic?
the portion of anesthetic that exerts a partial pressure

portion of anesthetic dissolved in the water of plasma after the lipophilic portions of the blood (proteins) have been saturated
what is the effect of lipophilicity on rate of induction of general anesthetics?
high lipophilicity -> saturates proteins (inactive reservoir) -> Part equilibrates with Palv -> slow induction

low lipophilicity -> only small amt goes to lipophilic portions of blood -> Part equilibrates with Palv -> rapid rate of induction
what are the stages in the equilibration of the partial pressure of an anesthetic that is inspired with the partial pressure of that anesthetic in the brain?
1) alveolar partial pressure of an anesthetic equilibrates with inspired partial pressure of the anesthetic
2) arterial partial pressure equilibrates with alveolar partial pressure
3) arterial partial pressure equilibrates with brain partial pressure
describe the equilibration of alveolar partial pressure of an anesthetic with the inspired partial pressure of the anesthetic
the particular anesthetic used plays a large role

loading dose can be used for a few minutes to decrease the time required for this equilibration
describe the equilibration of arterial partial pressure of an anesthetic with the alveolar partial pressure of the anesthetic
takes about ten seconds for the blood in lung capillaries to reach the capillaries of the systemic circulation

this equilibration occurs very quickly
describe the equilibration of arterial partial pressure of an anesthetic with the brain partial pressure of the anesthetic
particular anesthetic used plays little/no role on rime required

this equilibration occurs pretty quickly regardless of which anesthetic is used

since all general anesthetics are somewhat lipophilic, they cross the blood-brain barrier readily
what is the only way to increase the speed of recovery from a general anesthetic?
agents with a quick induction have a quick recovery

advantage to a quick recovery is that the patient passes through phase II (excitement phase) quickly
minimum alveolar concentration (MAC)
minimum concentration (partial pressure) of anesthetic necessary to prevent movement in response to surgical skin incision in 50% of patients (measure of potency of inhaled anesthetic)

1.3xMAC is used during surgery to prevent movement in 95% of patients
what is the most potent inhaled anesthetic?
methoxyflurane (1MAC = 0.16% of atmospheric pressure)
what is the least potent inhaled anesthetic?
nitrous oxide (fills any empty cavity b/c it is a gas where other anesthetics are volatile liquids)

1MAC = 101% of atmospheric pressure
can only go to 80%, therefore nitrous oxide is an incomplete anesthetic
how is MAC determined for mixtures of inhaled anesthetics?
MAC = minimum alveolar concentration
MACs are additive for the different anesthetics used
(e.g. 0.5MAC N2O + 0.5MAC halothane = 1.0MAC)
what is the advantage of mixing anesthetics?
reduces the side effects due to each drug
what is the effect of temperature on minimum alveolar concentration for inhaled general anesthetics?
at lower temperatures, the MAC is lower (patient is more sensitive to general anesthetics)

at higher temperatures, the MAC is higher
what is the effect of age on minimum alveolar concentration for inhaled general anesthetics?
as a patient gets older, the MAC decreases (elderly patients are more sensitive to general anesthetics than are young patients)
what is the effect of SNS/CNS altering drugs on the minimum alveolar concentration for inhaled general anesthetics?
pt with a blood-alcohol content of 0.2% requires a lower dose of general anesthetic

chronic alcoholic without alcohol for a couple days requires a higher dose of general anesthetic

patient on CNS-depressing drugs requires lower dose of general anesthetics

patient on CNS-stimulating drugs requires higher dose of general anesthetics
what is the effect of barometric pressure on minimum alveolar concentration for inhaled general anesthetics?
decreased barometric pressure results in increased MAC
what factors have no effect on the minimum alveolar concentration for inhaled general anesthetics?
1) duration of administration (length of surgery)
2) biotransformation (more drug is required, but MAC remains same)
3) gender
4) blood pressure
5) arterial oxygenation
6) level of ventilation
7) hemoglobin concentration (anemia doesn't affect MAC)
what is the Meyer-Overton theory of anesthesia?
developed in 1900

states that anesthetic dissolves in lipid membrane, causes expansion, and subsequently the reversible inhibition of synaptic transmission

changes the properties of the cell membrane rather than using a receptor

states that anesthetics increase the affinity of the GABA receptor for GABA and inhibit the excitatory (glutamate) receptors
how can the minimum alveolar concentration of an inhaled general anesthetic be predicted?
MAC x (oil/gas partition coefficient) = 1.3

can fit a logarithmic scale line very well, thus MAC is actually the partial pressure required to generate a particular concentration of anesthetic in a lipophilic medium (i.e. lipid bilayers of CNS)
what is the antagonist to general anesthetics?
since general anesthetics' effects aren't receptor-mediated, there is no antagonist to them
what is the effect of general anesthetics on the minute ventilation?
decreases tidal volume, which consequently decreases minute ventilation
what is the effect of general anesthetics on the respiratory rate?
increases the respiratory rate
what is the effect of general anesthetics on the arterial PCO2?
increases arterial PCO2, leading to undesirable CV effects (changes TPR and CO)
what is the effect of general anesthetics on the ventilatory response to carbon dioxide?
with increasing PaCO2, the minute ventilation increases in a linear manner (plot of minute ventilation vs. PaCO2); the effect of general anesthetics is to decrease the slope of this line, so that the increase in minute ventilation is less than that seen with a comparable increase in PaCO2 without general anesthetics
what is the effect of general anesthetics on the ventilatory response to hypoxemia?
general anesthetics abolish the ventilatory response to hypoxemia; usually the minute ventilation increases as a result of low PaO2 (curves up after a certain partial pressure), but with general anesthetics the minute ventilation remains constant regardless of how low the PaO2 gets
what is the only general anesthetic that doesn't increase PaCO2?
nitrous oxide (N2O)

advantage - can be used in combination with other general anesthetics to give anesthesia without causing the undesirable CV effects (changing TPR and CO)
for what reasons can nitrous oxide be used in combination with other general anesthetics?
1) decrease hypercapnea caused by other GAs
2) improve hypotension caused by other GAs
what is the only general anesthetic that doesn't decrease blood pressure?
nitrous oxide (it can be used in combination with other general anesthetics in order to decrease the hypotensive effects of the other general anesthetics)

all others decrease TPR
sevoflurane decreases CO
what are the effects of general anesthetics on the CNS? why is this undesirable?
general anesthetics cause an increase in cerebral blood flow

undesirable b/c intracranial tumors cause increasing pressures within a closed vault (skull) and if more blood is flushed into the skull, intracranial pressure rises to a dangerous level
what is the general anesthetic of choice for patients with high intracranial pressure (patients with tumors)?
isoflurane

b/c it doesn't cause as extensive elevation of intracranial pressure as the rest of the inhaled general anesthetics
what is the effect of general anesthetics on the kidneys?
general anesthetics decrease renal blood flow, but usually this isn't clinically significant because it doesn't cause any pathology
why is nitrous oxide combined with a narcotic (fentanyl) to be used as a general anesthetic?
the narcotic doesn't affect blood pressure or cardiac output
why is anesthetic metabolism important?
can have toxic effects on the kidneys and liver
what factors influence the extent of biotransformation of inhaled general anesthetics?
1) enzyme activity - genetic factors/enzyme inducers may determine an individual's ability to metabolize the compound

2) substrrate availability - poorly soluble anesthetics (low blood/gas partition coefficient) leave little substrate available for metabolism; these anesthetics are exhaled rapidly
halothane-associated hepatic dysfunction
rare dysfunction (1/30,000 pts treated), but is associated with high mortality

profile of affected patient:
middle-aged obese
female fever then jaundice
repeated exposure

unknown mechanism - reactive intermediates attach to liver cell membranes and exert toxic effects
what patients should not be given halothane?
a) morbidly obese
b) repeated exposure
c) liver disease
d) enzyme induction
biotransformation of methoxyflurane
very soluble drug (high oil/gas partition coefficient), so about 50% of the absorbed dose is metabolized

transformation frees up fluoride and increases serum concentration, causing neprotoxicity

never use methoxyflurane, but the important thing is that general anesthetics are metabolized and cause problems (e.g. the nephrotoxicity)
biotransformation of isoflurane
chemically and pharmacologically similar to enflurane

metabolism is minimal (about 0.17%)
biotransformation of sevoflurane
though it has a low blood/gas partition coefficient, a surprisingly large amount (3% of dose) is metabolized; this causes significant amounts of fluoride buildup in the blood during long surgeries
why would you not want to use sevoflurane in long surgeries?
though it has a very low blood/gas partition coefficient, a surprisingly large amount (3%) is metabolized, which causes significant amounts of fluoride to build up in the blood during long surgeries
biotransformation of desflurane
essentially no metabolism (0.02%)
why are IV anesthetics used, in general?
used for induction, so that you can skip phase 2 (excitement phase; nightmare)
what is the most commonly used ultra-short-acting barbiturate as a general anesthetic?
thiopental

crosses the blood-brain barrier and establishes a brain:plasma equilibrium within 1 minute because of high lipid solubility
why are barbiturates (thiopental) ultra-short-acting general anesthetics?
they rapidly diffuse out of the brain and other highly vascular tissues and are redistributed to muscle, fat, and eventually all body tissues
thiopental
ultra-short-acting barbiturate

used as an IV general anesthetic for induction

rapid redistribution causes this to be very short acting
propofol
drug of choice as an IV general anesthetic agent; great for inducing anesthesia

smaller doses widely used for sedation in ICU

oil at room temperature, supplied as an emulsion

more rapid emergence from anesthesia than with thiopental; also characterized by minimal postoperative confusion
what are the advantages of propofol over thiopental as IV general anesthetics?
more rapid emergence from anesthesia with propofol than with thiopental

minimal postoperative confusion associated with propofol
etomidate
IV general anesthetic used to induce anesthesia; also used in combination with succinyl choline for intubation in code situations

increases available GABA receptors, perhaps by displacing an endogenous GABA inhibitor

causes minimal respiratory and cardiovascular depression
malignant hyperthermia
dangerous increase in body temperature brought on by the use of anesthetics
- mainly determined by genetic predisposition of the patient
- caused by calcium leak from the SR of skeletal muscle causing massive contractions and heat production

Tx: dantrolene (stabilizes the SR membrane without interfering with action potentials - acts like a calcium channel blocker)
propofol
drug of choice as an IV general anesthetic agent; great for inducing anesthesia

smaller doses widely used for sedation in ICU

oil at room temperature, supplied as an emulsion

more rapid emergence from anesthesia than with thiopental; also characterized by minimal postoperative confusion
dantrolene
essentially a calcium-channel blocker, though it doesn't bind to the calcium channels; stabilizes the SR membrane without interfering with action potentials

used as a Tx for malignant hyperthermia
what are the advantages of propofol over thiopental as IV general anesthetics?
more rapid emergence from anesthesia with propofol than with thiopental

minimal postoperative confusion associated with propofol
etomidate
IV general anesthetic used to induce anesthesia; also used in combination with succinyl choline for intubation in code situations

increases available GABA receptors, perhaps by displacing an endogenous GABA inhibitor

causes minimal respiratory and cardiovascular depression
malignant hyperthermia
dangerous increase in body temperature brought on by the use of anesthetics
- mainly determined by genetic predisposition of the patient
- caused by calcium leak from the SR of skeletal muscle causing massive contractions and heat production

Tx: dantrolene (stabilizes the SR membrane without interfering with action potentials - acts like a calcium channel blocker)
dantrolene
essentially a calcium-channel blocker, though it doesn't bind to the calcium channels; stabilizes the SR membrane without interfering with action potentials

used as a Tx for malignant hyperthermia
propofol
drug of choice as an IV general anesthetic agent; great for inducing anesthesia

smaller doses widely used for sedation in ICU

oil at room temperature, supplied as an emulsion

more rapid emergence from anesthesia than with thiopental; also characterized by minimal postoperative confusion
what are the advantages of propofol over thiopental as IV general anesthetics?
more rapid emergence from anesthesia with propofol than with thiopental

minimal postoperative confusion associated with propofol
etomidate
IV general anesthetic used to induce anesthesia; also used in combination with succinyl choline for intubation in code situations

increases available GABA receptors, perhaps by displacing an endogenous GABA inhibitor

causes minimal respiratory and cardiovascular depression
malignant hyperthermia
dangerous increase in body temperature brought on by the use of anesthetics
- mainly determined by genetic predisposition of the patient
- caused by calcium leak from the SR of skeletal muscle causing massive contractions and heat production

Tx: dantrolene (stabilizes the SR membrane without interfering with action potentials - acts like a calcium channel blocker)
propofol
drug of choice as an IV general anesthetic agent; great for inducing anesthesia

smaller doses widely used for sedation in ICU

oil at room temperature, supplied as an emulsion

more rapid emergence from anesthesia than with thiopental; also characterized by minimal postoperative confusion
what are the advantages of propofol over thiopental as IV general anesthetics?
more rapid emergence from anesthesia with propofol than with thiopental

minimal postoperative confusion associated with propofol
etomidate
IV general anesthetic used to induce anesthesia; also used in combination with succinyl choline for intubation in code situations

increases available GABA receptors, perhaps by displacing an endogenous GABA inhibitor

causes minimal respiratory and cardiovascular depression
dantrolene
essentially a calcium-channel blocker, though it doesn't bind to the calcium channels; stabilizes the SR membrane without interfering with action potentials

used as a Tx for malignant hyperthermia
malignant hyperthermia
dangerous increase in body temperature brought on by the use of anesthetics
- mainly determined by genetic predisposition of the patient
- caused by calcium leak from the SR of skeletal muscle causing massive contractions and heat production

Tx: dantrolene (stabilizes the SR membrane without interfering with action potentials - acts like a calcium channel blocker)
dantrolene
essentially a calcium-channel blocker, though it doesn't bind to the calcium channels; stabilizes the SR membrane without interfering with action potentials

used as a Tx for malignant hyperthermia
use of opiates with regards to general anesthetics
used as a premedication for sedation and analgesia
use of benzodiazepines in regards to general anesthetics
used as a premedication for their anxiolytic effects
e.g. diazepam, lorazepam

additionally, midazolam causes amnesia in 20% of patients
usefulness of antimuscarinics in general anesthetics
e.g. atropine, glycopyrrolate

general anesthetics increase mucous secretions in lungs and causes patients to wake up with a dry mouth - antimuscarinics combat these effects
midazolam
benzodiazepine

useful as a premedication for general anesthetics for anxiolytic effects; also causes amnesia in 20% of patients
atropine
antimuscarinic

useful with general anesthetics to block mucous secretion in the lungs that is caused by the general anesthetics