INHALATION AGENTS Flashcards
Although the mechanism of action of inhalation
anesthetics remains unknown, it is assumed that their ultimate effect depends on ____________
Attainment of a therapeutic tissue concentration in the central
nervous system. T
There are many steps between the administration of an anesthetic from a vaporizer and its
deposition in the brain
FRESH gas flow is determined by the
Vaporizer and the flow meter settings
Inspired Gas concentration (FI) is determined by
Fresh Gas flow rate
Breathing circuit volume
Circuit absorption
Alveolar Gas concentration (FA) is determined by
Uptake
Ventilation
Concentration effect and 2nd Gas effect (concentrating effect, augmented inflow effect)
Fa (arterial gas concentration) is affected by
Ventilation/ Perfusion mismatching
What does (MAC) stand for?
Minimum alveolar concentration
MAC of Inhaled anesthetic is the
alveolar concentration that prevents movement in 50% of patients in response to a standardized stimulus (eg, surgical incision)
Why is MAC useful (MAP)
MAC is a useful measure because it
• Mirrors brain partial pressure
• Allows comparisons of potency between agents
• Provides a standard for experimental evaluations
Anesthetic uptake produces a characteristic curve that
relates the__________to ______
rise in alveolar concentration to time.
The shape of this graph (anesthetic uptake) is
determined by
The uptakes of individual tissue groups.
The rate of rise of anesthetic slows as the
Vessel-rich group—and eventually the muscle group
—reach their capacity.
Vessel rich group are _____kg and _______%CO
10kg; 75%
Muscle group are _____kg and _______%CO
50kg; 19%
Fat groups are _______ and _______% CO
20kg ; 5%
Vessel POOR group are ____kg and _____–% CO
20kg; 1%
The impact of tissue storage depends on
- the duration of anesthesia
2. Solubility of the anesthesia in various tissue compartments
The initial steep rate of uptake is due to
unopposed filling of the alveoli by ventilation.
Elimination of inhaled anesthetics is reflected by
the decrease in the alveolar concentration (FA) COMPARED WITH the concentration present at
the conclusion of anesthesia (FAO).
The most important route for elimination of inhalation anesthetics is
the alveolus.
Many factors that speed induction also speed recovery:
EHL LDHI
- Elimination of rebreathing
- High fresh gas flows
- Low anesthetic-circuit volume
- Low absorption by the anesthetic circuit
- Decreased solubility
- High cerebral blood flow (CBF)
- Increased ventilation.
An increase in the duration of anesthesia during a constant dose of anesthetic (1.6 MAC) is associated with
increases in the time to recovery, with the greatest increases occurring with the most blood-soluble anesthetics.
Decrease in MAP reflects a
decrease in Systemic Vascular Resistance (SVR) verses a
decrease in Cardiac Output
Halothane lowers MAP by________CO, whereas_______ is unchanged.
decreasing CO; SVR
Dose-dependent reduction of arterial blood pressure is due to _______
direct myocardial depression;
2.0 MAC of halothane results in a
50% decrease in blood pressure and cardiac output.
Halothane, Isoflurane, Desflurane, and Sevoflurane
on systemic vascular resistance (dynes/sec/cm5)
when administered to healthy volunteers.
Halothane (from 1200 to about 1100) Unchanged
Isoflurane (from 1400 to about 750)
Desflurane(From 900 to about 500)
Sevoflurane (From 990 to about 750)I
Decrease in MAP reflects a decrease in
Systemic Vascular Resistance (SVR) verses a decrease in Cardiac Output
Dose related decreases in SVR is minimized by:
substitution of Nitrous Oxide for a portion of Volatile Drug
Nitrous Oxide causes _______or______in MAP when administered alone
unchanged or mildly increases
Nitrous oxide (N2O; laughing gas) is the only
inorganic anesthetic gas in clinical use
• At low concentrations ( 0.25 mac) Isoflurane causes
linear, dose dependent heart rate increase
• Heart Rate increases minimally with
Desflurane concentrations of less than one MAC
• A dose dependents increase in Desflurane is reflected by a:
linear increase in Heart Rate
Inhaled anesthetics produce drug specific and dose-dependent
increases in PaCO2.
Gas exchange becomes progressively less efficient at
deeper levels of anesthesia
Substitution of Nitrous Oxide (60%) for equivalent portion of volatile anesthetic may attenuate
the increased Paco₂
Inhaled anesthetics produce similar dose-dependent
decreases in the ventilatory responses to carbon dioxide.
Blunting of ventilation with inhaled anesthetics may be
less pronounced in patients undergoing surgery
Volatile anesthetics all blunt the___________
ventilatory stimulation evoked by arterial hypoxemia
