Anesthetics UPTAKE Flashcards
What are 3 major factors affecting UPTAKE and DISTRIBUTION?
a. Solubility of the inhalation anesthetic agent
b. Patient’s cardiac output
c. partial pressure difference of the gas between the alveoli and pulmonary vein
What is the solubility of gas determined by
Blood-Gas partition Coefficient
What does the B/G partition Coefficient describes
Affinity of gas to blood
Isoflurane B/G partition coefficient of 1.4 , what does that mean?
At equilibrium, the isoflurane concentration in the
blood would be 1.4 times the concentration in the gas (alveolar) phase. By definition, the PARTIAL PRESSURE OF THE AGENT IN BLOOD AND GAS ARE IDENTICAL AT EQUILLIBRIUM but the blood would contain more isoflurane.
What is the relationship of B/G partition coefficient to blood solubility? How does it affect delivery of anesthetics?
The higher the coefficient number, the more soluble the anesthetic agent will be BLOOD at equilibrium.
Anesthesia onset will be DELAYED
What determines anesthesia, is it the amount of drugs in blood or the partial pressure of inhalation agent in the brain?
Partial pressure of inhalation agent in the (blood) and brain determines ANESTHESIA
What is the B/G Partition coefficient of Desflurane?
0.45
What is the B/G Partition coefficient of Nitrous?
0.47
What is the B/G Partition coefficient of Sevoflurane?
0.65
What is the B/G Partition coefficient of Isoflurane?
1.4
What is the B/G Partition coefficient of Enflurane?
1.8
A high partition coefficient means that
it takes more time to FILL the TANK, meaning that it will take time for the partial pressure to get high enough to induce anesthesia.
Is the FA/FI for high partition coefficient gas high or low? How does that affect the onset of anesthesia?
Low , because the gas dissolve quickly in the BLOOD , which delays onset of anesthesia?
Uptake of soluble inhalation agents can be increased also by what?
by anesthetic overpressuring, that is, delivering a concentration of inspired gas two to four times the MAC
The rate of rise of Fa/Fi over time for most agents correlates_______with the relative solubility of the anesthetic agents.
inversely
Explain how an increase in Cardiac Output affects FA/FI?
As cardiac output increases, more blood travels through the lungs, thereby removing more anesthetic from the gas phase and resulting in a lower FA and a slower rate of FA increase
What has the MOST PRONOUNCED effect on the uptake of more soluble anesthetic?
Changes in Cardiac Output (CO)
What determines DELIVERY to the tissue? Explain how it relates to what happening to the FA/FI?
- Alveolar-VENOUS anesthetic gradient
- As the alveolar-venous anesthetic gradient approaches 0 means that TISSUES ARE SATURATED, means that UPTAKE OF ANESTHETIC IN BLOOD has stopped and FA/FI should be approaching UNITY or be closer to 1
CO mostly affect
SOLUBLE AGENTS
Explain how a decrease in CO affect FA/FI?
Less blood flow to the lungs, less anesthetics TAKEN UP by the lungs, Alveolar concentration is achieved quicker.
For Less soluble anesthetic, the rate of Fa/Fi increase is rapid and does not depend on ________.
Cardiac Output
With highly soluble agents, a potentially dangerous
positive feedback exists. Explain.
Anesthetic-induced cardiac depression decreases uptake, increases alveolar concentration, and further depresses
cardiac output.
Vessel RICH group received _____%of CO
75% of CO
Muscle group received ____-%of CO
19%
Explain the path when anesthetic agent are delivered?
The anesthetic agent in the blood first go to the vessel- rich tissues (lungs, heart, brain) Then after blood returns to the lungs, depending on its blood-gas partition coefficient, it has the same partial pressure that it had on leaving the lungs. As the gradient for the uptake of anesthetic approaches 0, less agent is taken up, and alveolar concentration rises
FA/FI and children, explain.
Children have greater perfusion of the vessel rich
group than do adults, GREATER CO to Fa/Fi rises more rapidly in children, so anesthesia is achieved more rapidly in these patients.
IN CHILDREN IT’S the OPPOSITE, CO increase FA/FI
