34 - Anesthesia Flashcards Preview

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1

List the general characteristics of general anesthesia.

1. Reversible
2. Failure to respond to a noxious stimulus
3. Blockage of cardiovascular, g.i. and respiratory reflexes
4. Amnesia
5. Loss of consciousness

2

List desirable actions in general anesthetics.

1. Loss of consciousness
2. Analgesia
3. Amnesia
4. Muscle relaxation

3

No single agent has yet been identified as

An ideal anesthetic

4

What are the stages of anesthesia?

1. Analgesia
2. Excitement
3. Surgical anesthesia (4 planes)
4. Imminent death

5

Describe some signs and reflex reactions characterizing stage 1 of anesthesia: analgesia

1. Normal respiration
2. Voluntary control of OCM
3. Normal pupil size
4. Normal eye reflexes
5. Normal muscle tone
6. Normal respiratory response to skin incision

6

Describe some signs and reflex reactions characterizing stage 2 of anesthesia: excitement

1. Unstable respiration
2. Voluntary control of OCM begins to decrease
3. Very dilated pupil size
4. Lid begins to close
5. Tense struggle to maintain muscle tones
6. Normal respiratory response to skin incision

7

Describe some signs and reflex reactions characterizing plane 1 of stage 3 of anesthesia: surgical anesthesia plane 1

1. Normal respiration
2. OCM decreasing
3. Pupil shrinking
4. Corneal eye reflexes begin to dip
5. Muscles begin to get more flaccid
6. Decreasing respiratory response to skin incision

8

Describe some signs and reflex reactions characterizing stage 3, plane 2 of anesthesia: surgical anesthesia plane 2

1. Respiration decreasing
2. No OCM
3. Pupil is extremely shrunken
4. Little to no corneal response, pupillary light response decreasing
5. Decreasing muscle tone
6. Decreasing respiratory response to skin incision

9

Describe some signs and reflex reactions characterizing stage 3, plane 3: surgical anesthesia, plane 3

1. Little to no intercostal respiration, increasing diaphragmatic respiration
2. No OCM
3. Increasing pupil size
4. Decreasing pupillary light
5. Decreasing muscle tone
6. No response to skin incision

10

Describe some signs and reflex reactions characterizing stage 3, plane 4 of anesthesia: surgical anesthesia, plane 4

1. No intercostal respiration, decreasing diaphragmatic respiration
2. No OCM
3. Very dilated pupil
4. Little to no light reflex
5. Little to no muscle tone
6. No response to skin incision

11

Describe some signs and reflex reactions characterizing stage 4 of anesthesia: imminent death

1. Apnea (no respiration)
2. No OCM
3. Extremely dilated pupils
4. No light reflex
5. Complete flaccid muscles
6. No response to skin incision

12

Describe the 2 common anesthetics.

1. Anesthetic gases (eg. Nitrous oxide) - administered via inspired air
2. Volatile anesthetics (egs. Halothane, enflurane) - administered by first being vaporized then administered via inspired air

13

What general factor does anesthesia depend on and why?

The brain (or spinal cord) concentration of inhalational anesthetic. Anesthetic must partition from inspired air into blood water and then from blood into brain.

14

Uptake of anesthetic into brain depends on:

1. The concentration of anesthetic in inspired air
2. The rate of pulmonary ventilation
3. Cardiac output
4. Solubility of anesthetic in air, water, lipid.

15

How is anesthetic solubility described?

1. Blood/gas partition coefficient (Pb/g) determines blood anesthetic levels.
2. Oil (lipid-like)/gas partition coefficient (Po/g) determines brain anesthetic levels and thus anesthetic potency.

16

How are most anesthetics removed from the body?

By exhalation

17

Describe another way that a drug may be removed from the body than exhalation and give examples.

Metabolization

1. Methoxyflurane - 50% metabolized

2. Isoflurane - 0.2% metabolized

18

Describe what MAC is

Minimum alveolar concentration - the minimum concentration in the alveolus that prevents 50% of patients from responding to a painful stimulus.

19

What is MAC used for?

To compare potencies of different anesthetics

20

Describe the Meyer-Overton correlation

As oil:gas partition coefficient rises, MAC atm decreases.

21

What does low MAC indicate?

Greater potency (lower concentration required to prevent 50% patients’ response to painful stimulus)

22

What are the two types of theories of volatile anesthetic action?

1. Lipid-based
2. Protein-based

23

Describe the lipid bilayer expansion hypothesis of anesthetic effect.

Anesthetic molecules accumulate in the hydrophobic region of lipid membrane, causing the volume of the hydrophobic region to expand to the point in which the functions of membrane ion channels are reversibly altered, providing anesthetic effect.

24

Describe the protein-related theory of anesthetic effect.

Single amino acid substitutions at two positions remove the potentiating effects of volatile anesthetics and ethanol at GABAa and glycine receptors.