VOLATILE ANESTHETICS

QUESTION 1: The current theories of the mechanism of general anesthesia suggest that all volatile anesthetics: (select all that apply)
1. act at a specific receptor
2. act primarily in the reticular activating system
3. depress release of neurotransmitters
4. affect synaptic transmission

QUESTION 2: The MAC value for isoflurane is: (select all that apply)
1. highest in the young
2. decreased at age 70 compared to age 20
3. decreased at lowered body temperature
4. decreased by administration of 70% nitrous oxide

QUESTION 3: A patient is to have a cholecystectomy.  The anesthesiologist decides to use sevoflurane in oxygen as the sole anesthetic agent, with no other medications administered.  Approximately what concentration of sevoflurane will be required to prevent movement in response to intubation?
A. 1.75%
B. 2.25%
C. 3%
D. 4%
E. 5%

ANSWER 1: (4) It is thought that all volatile anesthetics affect synaptic transmission.  Excitatory synapses are depressed by general anesthetics while inhibitory synapses may be depressed or potentiated.  There is no specific receptor konwn for volatile anesthetics, and no definite location within the CNS is thought to be responsible for their actions.

ANSWER 2: (1, 2, 3, 4) The MAC value is highest in the very young child and decreases as one gets older.  It is also decreased by lower body temperature.  Nitrous oxide in 70% concentration decreases MAC for a given agent.

ANSWER 3: (C) MAC is defined in terms of the prevention of movement in response to skin incision.  The concentration necessary to prevet movement in response to a greater stimulus, such as intubation, is approximately 1.5 times the values for MAC.

REFERENCE:

McGraw-Hill Specialty Board Review