general anesthetics

Question 1

What types of drugs are used mainly to induce anesthesia?

Answer 1

inhalation anesthetics - sevoflurane, desflurane, isoflurane, nitrous oxide
intravenous anesthetics - propofol, etomidate, ketamine, barbiturates, benzodiazepines, opioids

Question 2

What kinds of adjunct drugs can be added to the regimen (balanced anesthesia) while the patient is anesthetized?

Answer 2

amnesia and loss of consciousness - sedative-hypnotics
analgesia - opioids
muscle relaxation - neuromuscular blockers
suppression of autonomic responses to pain - antimuscarinics (e.g. atropine)

Question 3

What is the current hypothesis of the mechanism of action of inhalation anesthetics?

Answer 3

enhancement of inhibitory channels: GABA-A receptors in the brain and glycine receptors in the spinal cord
inhibition of excitatory channels: AMPA and NMDA glutamate receptors

Question 4

What is the reference dose of inhalation anesthetics? How is a dose of inhalation anesthetic measured?

Answer 4

Minimal Alveolar Concentration (MAC) - the concentration of the gas in the alveoli that produces no movement in response to a standardized painful stimulus in 50% of the population
All doses of inhalation anesthetics are multiples of the MAC

Question 5

As the dose of inhalation anesthetic increases, how does the body respond?

Answer 5

lowest dose - losing perceptive awareness -> losing movement in response to painful stimulus -> losing autonomic reactions

Question 6

What pharmacokinetic information does an inhalation anesthetic’s oil:gas coefficient tell you?

Answer 6

Tells you about the potency of the drug.

The higher the oil:gas coefficient, the higher the potency of the drug (and the lower the MAC)

Question 7

What pharmacokinetic information does an inhalation anesthetic’s blood:gas coefficient tell you?

Answer 7

Tells you how soluble the drug is in blood which is inversely proportional to how fast the drug induces anesthesia and how fast patient recovers from the anesthesia
A low solubility drug (low blood:gas coefficient) will induce anesthesia FAST and recover FAST
A high solubility drug (high blood:gas coefficient) will induce anesthesia SLOWLY and recover slowly (used for maintenance)

Question 8

What is diffusion hypoxia? What can you do to prevent it?

Answer 8

When a patient is coming out of nitrous oxide induced anesthesia, the nitrous oxide dilutes the oxygen and CO2 in the alveolar air. This does two things:
1) decreases the partial pressure of oxygen which decreases the driving force for dissolving oxygen in the blood.
2) decreases the partial pressure of CO2 which decreases the respiratory drive
Both of these would lead to low levels of oxygen in the blood and tissues
Prevent with making the patient breath full oxygen during termination of nitrous oxide

Question 9

What is the second gas effect?

Answer 9

During induction, nitrous oxide is much more soluble than nitrogen so it diffuses into the blood more than nitrogen diffuses out. This creates a partial vacuum which increases the ventilation rate.
Increasing the ventilation rate will increase the delivery rate and thus increase the rate of equilibration of a second inhaled anesthetic.

Question 10

What are the effects on inhalant anesthetics on the cardiovascular system? Kidney? Respiration

Answer 10

Decrease blood pressure, decreased CO (except nitrous oxide)
decreased renal blood flow and GFR
Decreased spontaneous respiration (except nitrous oxide)
Decreased ventilatory response to CO2