GA 2 Flashcards
Signs of development of general anesthesia
- Loss of fine motor function/coordination
- Alteration of consciousness/analgesia
- Loss of temperature regulation
- Unconsciousness
- Changes in eye motion
- Loss of muscle tone
- Respiratory failure*
- CV failure*
- Coma and death*
- occur with overdose
Time course of surgical anesthesia
• Induction: time between initiation of administration of anesthetic and attainment
of surgical anesthesia, that is, until Stage III is reached
• Maintenance: time during which surgical anesthesia is in effect (surgery carried
out during this period)
• Recovery: time following termination of administration of anesthetic until
complete recovery of patient from anesthesia
Phase I: lung factors
The rate of increase in the partial pressure of anesthetic gas in the alveoli and pulmonary capillary blood is proportional to the rate of ventilation (respiratory minute ventilation). The rate of induction of anesthesia can be increased by over-ventilation. The depth of anesthesia is not affected by ventilation rate.
Recovery from anesthesia is also proportional to rate of ventilation. Thus respiratory
depression as a consequence of overly deep anesthesia can prolong the recovery
time
Solubility in blood
The blood:gas partition coefficient (λ) is a measure of the solubility of anesthetic gas in blood. The blood:gas partition coefficient is defined as the concentration of anesthetic in blood divided by anesthetic concentration in the
inspired gas mixture.
Important point: induction of anesthesia is ______
slower for a more soluble anesthetic gas.
Higher GA solubility in blood, means that ______ in blood
in order to reach stage III, surgical anesthesia:
more anesthetic must be dissolved
Descending depression
loss of fine motor function and
progressive loss of function from higher (e.g., cognition
and consciousness) to lower (e.g., respiratory control) levels within the central
nervous system.
impairment of coordination • alteration of consciousness and often analgesia • loss of temperature regulation • unconsciousness • effects on eye motion, pupil size and light reflex • loss of muscle tone • respiratory failure • cardiovascular failure • coma and death
The rate at which an effective concentration of anesthetic is reached in the brain
depends upon 5 factors:
(1) concentration of the anesthetic in inspired air,
(2) alveolar ventilation rate,
(3) pulmonary blood flow (cardiac output),
(4) blood:gas partition coefficient, and
(5) potency (oil:gas partition coefficient).
- A high-solubility GA (halothane) exhibits a slower approach to equilibrium because_________
- A low-solubility GA (nitrous oxide), exhibits a more rapid increase in its partial pressure in blood.
a larger amount must be dissolved in blood
• Combining the effects of blood solubility and pulmonary flow:
the rate of transfer of volatile anesthetic from alveoli to blood is inversely related to both pulmonary blood flow and the solubility of the anesthetic gas in blood.
Pharmacokinetics of GA uptake: Summary
Rate of induction depends on uptake, distribution, and potency of inhaled
anesthetic
• High solubility and large volume of distribution of GA in fatty tissue, and low
perfusion of fatty tissue, produces
slow uptake and elimination from fatty tissue
• Uptake proceeds through 3 compartments
vessel-rich including brain, muscle
group, fat group)
↓cardiac output
↑uptake of inhaled anesthetic
• ↑rate and depth of alveolar ventilation
↑rate of rise in arterial GA anesthetic
