Volatile Anesthetics Flashcards
T/F
At equilibrium, the CNS partial pressure of inhaled anesthetics equals their arterial partial pressure, which in turn equals their alveolar partial pressure if
cardiopulmonary function is normal.
T
Major determinants of the speed of induction
- inspired concentration
2. blood:gas solubility
Most potent of the volatile anesthetics in clinical use
Isolurane
Is the least soluble volatile anesthetics
Deslurane
Least irritating volatile anesthetics to the airways
Sevolurane
Nitrous oxide (N2O) can expand a pneumothorax to double or triple its size in 10 to 30 minutes, and washout of N2O can lower alveolar concentrations of oxygen and carbon dioxide, a phenomenon called
Diffusion hypoxia
Is the alveolar concentration of an inhaled anesthetic at one atmosphere that prevents movement in response to a surgical stimulus in 50% of patients.
Minimum alveolar concentration (MAC)
Excluding data in patients <1 year of age (where MAC is lower than in older children), MAC decreases approximately ___ per decade.
6%
CO2 absorbents degrade sevolurane, deslurane, and isolurane to carbon monoxide when the normal water content of the absorbent (13% to 15%) is markedly decreased to how many percent?
<5%
As the tissues with lower perfusion rates absorb the drug, maintenance of equilibria throughout the body requires drug transfer from highly perfused compartments back into the bloodstream.
This lowering of drug concentration in one compartment by delivery into another compartment is called ____________.
redistribution
Technically, of the inhaled anesthetics only ____ & _____ are true gases
N2O and xenon
At equilibrium, the pressure exerted by molecular collisions of the gas against thecontainer walls is the ________
Vapor pressure
For all of the potent agents, at ___ the vapor pressure is below atmospheric pressure.
20°C
The ______ of a liquid is the temperature at
which its vapor pressure exceeds atmospheric pressure in an open container.
boiling point
Deslurane is bottled in a special container because its
boiling point of _____ makes it boil at typical room temperatures.
23.5°C
For any mixture of gases in a closed container, each gas exerts a pressure proportional to its fractional mass. This is its ____________.
Partial pressure
The sum of the partial pressures of each gas in a mixture of gases equals the total pressure of the entire mixture (______ law).
Dalton’s
Refers to the pressure of the gas in the gas phase
(if it were present) in equilibrium with the liquid.
Partial pressure
Is the term used to describe the tendency of a gas to equilibrate with a solution, hence determining its concentration in solution.
Solubility
_____ expresses the relationship of concentration
of a gas in solution to the partial pressure of the gas with which the solution is in equilibrium
Henry’s law
The principles of partial pressures and solubility apply in mixtures of gases in solution.
That is, the concentration of any one gas in a mixture of gases in solution depends on two factors:
(1) its partial pressure in the gas phase in equilibrium with the solution
(2) its solubility within that solution
The vascular system delivers blood to three physiologic tissue groups:
- vessel-rich group (VRG)
- muscle group
- fat group
In reality, the fat solubilities provide little inluence on emergence in cases lasting < ___ hours since the delivery of anesthetic to fat tissue is extremely slow as a result
of low blood low.
4
Read:
There are two ways to speed the equilibration of FA with FI, that is, to decrease time. One way is to increase minute ventilation, and the other is to decrease FRC.
Both of these methods can be used to speed induction by mask; the patient can exhale deeply before applying the mask (to decrease the initial FRC), and the patient
can breathe deeply and rapidly (to increase) after the mask is applied.
One of the reasons that pediatric inductions by spontaneous breathing of inhaled anesthetics are so much quicker than adult inductions is that the low FRC relative to VA of children makes for a low time constant, and hence a more rapid increase in FA/FI.
Read:
The more soluble the inhaled anesthetic, the larger the capacity of the blood and tissues for that anesthetic, and the longer it takes to saturate at any given delivery rate.
Since uptake is proportional to tissue solubility, the less soluble the anesthetic (such as deslurane), the lesser its uptake and the faster it reaches equilibrium
The most important factor in the rate of rise of FA/FI is _________
The uptake of anesthetic from the alveoli into the bloodstream
The ______ equation applied
to blood uptake of inhaled anesthetics.
The greater the value of VB (blood uptake), the greater the uptake from alveoli to blood, and the slower the
rise in FA/FI.
Fick
As blood is equilibrating with alveolar gas, it also begins to equilibrate with the VRG, muscle, and, more gradually, the fat compartments based on perfusion.
Although both VRG and muscle are lean tissues, the muscle compartment equilibrates far more slowly than the VRG.
The explanation comes in part due to the mass of the compartments relative to perfusion. The perfusion of the VRG is about _____ mL/min/100 g of tissue, whereas it is only ____ mL/min/100 g of tissue in the muscle.
75
3
What volatile anesthetic represents an exception. Its partition coeficients are fairly similar in each tissue: It does not accumulate to any great extent and is not a very potent anesthetic.
Its utility lies as an adjunct to the potent agents, and as a vehicle to speed induction.
Nitrous oxide
In overpresssurization and concentration effect, The higher the FI, the greater the effect. Thus what volatile anesthetic, typically given in concentrations of 50% to 70%, has the greatest concentrating effect.
N2O
This is not the complete picture; there is yet another factor to consider to the concentrating effect of a gas. As gas is leaving the alveoli for the blood, new gas at
the original FI is entering the lungs to replace that which is taken up by the blood.
This other aspect of the concentration effect has
been called ________________.
Augmented gas inlow
Read (Ventilation effects):
The greater the solubility of an inhaled anesthetic, the more rapidly it is absorbed by the bloodstream, such that anesthetic delivery to the lungs may be rate limiting to the rise in FA/FI.
Therefore, for more soluble anesthetics, augmentation of anesthetic delivery by increasing minute ventilation also increases the rate of rise in FA/FI.
Read (Perfusion effects):
For the less soluble agents, changes in cardiac output do not affect the rate of rise of FA/FI to a great extent, but for the more soluble agents the effect is noticeable.
As inspired concentration increases, greater cardiovascular depression reduces anesthetic uptake and actually increases the rate of rise of FA/FI. This positive feedback can rapidly lead to profound cardiovascular depression.
