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Flashcards in GA 2 Deck (36):
1

Signs of development of general anesthesia

1. Loss of fine motor function/coordination
2. Alteration of consciousness/analgesia
3. Loss of temperature regulation
4. Unconsciousness
5. Changes in eye motion
6. Loss of muscle tone
7. Respiratory failure*
8. CV failure*
9. Coma and death*

* occur with overdose

2

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

3

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

4

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.

5

Important point: induction of anesthesia is ______

slower for a more soluble anesthetic gas.

6

Higher GA solubility in blood, means that ______ in blood
in order to reach stage III, surgical anesthesia:

more anesthetic must be dissolved

7

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

8

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).

9

• 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

10


• 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.

11

Pharmacokinetics of GA uptake: Summary

Rate of induction depends on uptake, distribution, and potency of inhaled
anesthetic



12

• 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

13

• Uptake proceeds through 3 compartments

vessel-rich including brain, muscle
group, fat group)

14

↓cardiac output

↑uptake of inhaled anesthetic

15

• ↑rate and depth of alveolar ventilation

↑rate of rise in arterial GA anesthetic

16


• ↓GA solubility in blood (blood:gas partition)

speeds induction of anesthesia

17

• ↑ inspired GA ↑ rate of induction by

↑rate of anesthetic entry into arterial blood

18

_____ is related to kinetics of GA uptake and elimination

• blood:gas partition coefficient

19

oil:gas partition coefficient is an index

of GA potency

20

• Anesthetic potency is related

to 1/MAC

21

Clearance by___ is major route of removal for the volatile anesthetics

lungs

22

• Low potency – have to breathe a lot
• excellent analgesic
• Useful as adjunctive agent (anxiolytic and analgesic properties). Great for suppressing pain (dentists can use).
• Rapid onset and recovery
• Odd PK: Concentration effect, diffusion hypoxia and second gas effect

NO

23

MAC is 105%-->can’t be used as sole anesthetic agent

CI: respiratory obstruction, COPD, pregnancy (since you have to breathe so much of this).

NO

24

(i) Concentration effect:

∼1 liter/min of N20 taken up, owing to high inspired % (maybe 75%)
Big anesthetic vol. taken out of lung into blood, sucks more N2O gas into lung
Thus, uptake rate is faster than predicted

NO

25

ii) Diffusion hypoxia

when anesthetic administration is terminated
Large N2O volume leaving blood expands lung and dilutes alveolar O2 - hypoxia

NO

26

iii) Second gas effect

Like concentration effect, but with 2 gaseous GAs (75% N2O, 1% halothane)
Huge volume uptake rate of N2O sucks more of both gases into lungs
Thus, uptake of halothane is increased over expected value alone

NO

27

MAC = 0.75%
Not a good analgesic

Hepatotoxic

Malignant hyperthermia

Halothane

28

Moderate to high potency

poor analgesic

Low blood:gas partition coefficient

Halothane

29

Somewhat more potent
Less incidence of hepatotoxicity, renal toxicity
Little seizure propensity

Isoflurane (Forane

30

pleasant odor – no coughing – so can be used for induction
• Drawback: chemically unstable, releases fluoride ions, which are toxic to kidneys

Sevoflurane

31

Drugs used for surgery
benzodiazepines

diazepam (Valium®), midazolam, lorazepam
- used preoperatively to ease induction or for sedative purposes

32

Drugs used for surgery
Induction agents:

rapid deep anesthesia (20 sec), avoiding excitation/delirium
-- thiopental, propofol

33

Drugs used for surgery
Analgesics:

- opioids: morphine, fentanyl (latter has advantageously short duration of action)

34

Drugs used for surgery
Neuromuscular blockers:

relax skeletal muscle, particularly for abdominal surgeries
-- D-tubocurarine, vecuronium, succinylcholine

35

Drugs used for surgery
Anticholinergic drugs:

reduce GA-induced hypotension, bradycardia, and excess
salivary secretions that can choke patient during anesthesia
-- glycopyrrolate, atropine, scopolamine

36

Drugs used for surgery
Anti-emetics

reduce post-operative nausea and vomiting (common problem)
-- ondansetron (5-HT3–type serotonin receptor antagonist)