inhaled 2 Flashcards
decreased rate of rise of FA/FI means
slower induction
what causes a decreased rate of FA/FI
increased CO, increased FRC, decreased fresh gas flow. (think slow wash in and fast uptake)
increased rate of rise of FA/FI means
faster induction
what causes an increased rate of FA/FI
decreased time constant, decreased anatomic dead space, increased alveolar ventilation (think fast wash in and slow uptake)
what is the Fi
inspired gas
Fi (inspired gas concentration) is determined by
FGF rate, breathing circuit volume, and circuit absorption
FA (alveolar gas concentration) is determined by
uptake, ventilation, and the concentration effect and second gas effect
concentration effect has to do with how gases travel from ___ to ___
lungs,blood
how does the concentration effect promote the rapid induction in anesthesia
increased inspired volumes promotes an increase in alveolar partial pressure (PA) and helps to offset the decrease in partial pressure of the gases brought on by pulmonary capillary uptake
higher concentrations —> ____ uptake
greater
the rate at which the alveolar pressure of the anesthetic rises is determined by what 2 factors?
inspired concentration (what you turn your dial to) and alveolar ventilation (how often/how much you are ventilating the alveoli.
the faster you replenish the concentration in the alveoli, the ___ the induction
faster
Second Gas Effect
the rapid crossing of N20 into the blood tends to pull the second gas along with it. so the arterial partial pressure of the second gas rises more rapidly than it would if it were alone in the alveoli.
3 factors determine how rapidly anesthetics pass from the inspired gas to the blood:
solubility of the agent, rate blood flow thru the lungs (CO), partial pressure of the agents in the arterial/venous blood (whatever is in the blood already)
the blood:gas partition coefficient represents the ratio between
concentration in the blood to anesthetic concentration in a gas (alveolar) when the two are in a state of equilibrium. (Pa/PA)
CO - The higher the blood flow, the more blood that is exposed to the agent, the ___ the agent is picked up from the alveoli and delivered to the tissues
faster
as the venous partial pressure rises, there Is ___ picked up from the alveoli and uptake _____
less, decreases. (think: the gradient is less as tissues are becoming saturated and the venous blood returning has a higher partial pressure.)
solubility of the gas in tissues is which coefficient
oil:gas
the higher the blood flow to a particular tissue, the ___ the anesthetic is delivered and the ___ the partial pressure and concentration will rise in that area
faster, faster
the rate at which the partial pressure in the blood and tissues equalize is determinedly 2 things:
solubility of gas in tissues and tissue blood flow.
The rise in alveolar (FA) anesthetic concentration toward the inspired (Fi) concentration is most rapid with the ___ soluble agents
least. nitrous is fastest. (it has to do with the amt that can be dissolved in the blood)
the moderately soluble anesthetic agents (such as iso) have a ___ rate of Fa to Fi rise
slower (think this is why we use nitrous for the second gas effect, because these gases are slow, bc they have a higher blood:gas coefficient)
the higher the blood:gas coefficient, the ___the uptake
slower
