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15 Cards in this Set

  • Front
  • Back
What is the principal objective of inhalational anesthesia?
To achieve a constant and optimal brain partial pressure of the inhaled anesthetic.
What is alveolar partial pressure or partial pressure of the brain of inhaled anesthetics equal to?
Input (delivery) into alveoli minus uptake (loss) of the drug from alveoli into arterial blood
What is input into alveoli dependent on?
1. inhaled partial pressure (PI)
2. alveolar ventilation
3. characteristics of anesthetic breathing (delivery) system
4. patient's FRC
What characteristics influence uptake of the inhaled anesthestic to pulmonary capillary blood?
1. solubility of anesthetic in body tissues
2. cardiac output
3. alveolar to venous partial pressure differences (A-vD)
What is the concentration effect?
It is the impact of inhaled partial pressure (PI) on the rate of rise of the alveolar partial pressure of an inhaled gas. The higher the PI, the more rapidly the alveolar partial pressure of the gas approaches PI
What is the second-gas effect?
It reflects the ability of high-volume uptake of one gas to accelerate the rate of increase of increase of the P(alveolar) of a concurrently administered companion gas.
What are the characteristics of the anesthetic breathing system that influence the rate of increase of P(alveolar)?
1. volume of external breathing system
2. solubility of inhaled anesthetics in the rubber or plastic components of the breathing system
3. gas inflow from the anesthetic machine
What is a partition coefficient?
It is a distribution ratio describing how the inhaled anesthetics distributes itself between two phases at equilibrium; reflects relative capacity of each phase to accept anesthetic and is temperature dependent (solubility of gas in a liquid decreases as temp of liquid increases)
What is the overpressure technique?
Increasing the PI above what is required for maintenance of anesthesia to speed induction of anesthesia in agents that have higher blood solubility
What is the time constant?
It the amount of inhaled anesthetic that can be dissolved in the tissue divided by the tissue blood flow.
What is the impact of cardiac output on the induction of anesthesia?
Increased CO--> rate of increase in P (alveolar) slowed and induction of anesthesia slowed in highly soluble anesthetics
What do the pharmacokinetics of the elimination of inhaled anesthetics depend on?
Length of administration and the blood-gas solubility of the inhaled anesthetic
When does diffusion hypoxemia occur and what is it?
It occurs when the inhalation of nitrous oxide is discontinued abruptly leading to a reversal of partial pressure gradients such that nitrous oxide leaves the blood and enters the alveoli. The initial influx of NO into alveoli dilutes the PaO2 and PaCO2-->
hypoxia and decreased stimulus to breathe due to reduced CO2
What is MAC?
MAC (minimal alveolar concentration) is defined as the concentration at 1 atmosphere that prevents skeletal muscle movement in response to a supramaximal painful stimulus (surgical skin incision) in 50% of patients; varies only 10-15% between people
Action of inhaled anesthetics on which receptors contribute to immobility?
alpa-2 receptors and 5-HT receptors