Anes. Pharm II > Inhalation Agents/ MAC > Flashcards

Inhalation Agents/ MAC Flashcards

(39 cards)

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1
Q

ideal inhaled anesthetic

A
  • Nonflammable
  • Easily vaporized at ambient temperature
  • Potent
  • Low blood solubility to assure rapid induction and recovery from anesthesia
  • Minimal metabolism
  • Compatible with epinephrine
  • Skeletal muscle relaxation
  • Suppresses excessive sympathetic nervous system activity
  • Not irritating to airways
  • Bronchodilation
  • Absence of excessive myocardial depression
  • Absence of cerebral vasodilation
  • Absence of hepatic and renal toxicity
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2
Q

advantages of Halothane

A

nonflammable,
less pungent,
less soluble,
decreased toxicity;

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3
Q

disadvantages of halothane

A

decreased CO and increased arrhythmias (hepatotoxicity)

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4
Q

effects of increased fluorination

A
  • Nonflammable
  • Decreased solubility – MAIN ADVANTAGE***
  • Decreased potency – increased MAC
  • Less toxic due to resistance to degradation
    - Desflurane – yes
    - Sevoflurane – no
  • Decreased percentage metabolized
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5
Q

MAC definition

A

Minimum alveolar concentration (partial pressure) of an inhaled agent at 1 atmosphere that prevents skeletal muscle movement in response to a noxious stimulus in 50 percent of patients. (ED50 and mac have indirect relationship)

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6
Q

As potency increases, MAC…..

A

decreases

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7
Q

10-30% greater concentration than MAC produces

A

immobility in 90-95% of patients

1.1 to 1.3*** MAC

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8
Q

Why 50% immobile versus 95% immobile?

A

o Less variability
o Takes fewer subjects to determine MAC

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9
Q

What portion of the central nervous system determines MAC?

A

o Spinal cord excitability is decreased resulting in immobility
o Perfusion of the brain alone with ordinary concentrations does NOT produce immobility. Took up to 3-6X MAC.

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10
Q

Why minimal ALVEOLAR concentration?

A
  • Alveolar reflects the concentration at the cord or the brain most accurately.
    o Must allow for equilibration (generally about 10-15 minutes)
    o Dependent on agent – 3-4 time constants
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11
Q

As age increases, MAC?

A

decreases about 6% per decade

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12
Q

What does nitrous oxide do to MAC?

A

decreases MAC in all ages, but more so in the elderly.

o 60% nitrous oxide causes about a 60% reduction in MAC normally – more so in elderly.

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13
Q

MAC - Greatest to least

A

infants > children > neonates > adults

  • MAC is greatest in patients less than a year of age and decreases by nearly 50% in the elderly years.
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14
Q

How does temperature affect MAC?

A
  • Body temperature reduction causes MAC reduction.
  • MAC of desflurane is decreased almost in half by a 10 degree C decrease in temp.
  • MAC of nitrous oxide is not as affected ***
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15
Q

how does pregnancy affect MAC?

A

o Decreases MAC due to increased concentrations of progesterone
o Decreases nearly 30% through early postpartum; normalizing within 12*-72 hours.

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16
Q

how does decreased CNS sodium affect MAC?

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A

o Decreased MAC
o Possible causes – dehydration, absorption of irrigant

17
Q

how does opioids affect MAC?

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A

o Opioids – synergistic effect
- Even small dose (fentanyl 3mcg/kg) causes big decrease in MAC (almost 50% reduction for desflurane from 6.3 to 3.2%)
- However, a dose of 6mcg/kg causes a decrease from 6.3 to 2.2%
- Ceiling effect on MAC

18
Q

benzos with MAC?

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A

dose dependent decrease

19
Q

barbs, propofol, acute ETOH ingestion with MAC?

20
Q

LA with MAC?

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A

lidocaine IV decreases MAC

21
Q

Nitrous oxide with MAC?

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A

0.5 MAC of nitrous oxide plus 0.5 MAC of isoflurane are additive to 1 MAC of either drug alone

22
Q

Alpha 2 agonists - Clonidine and dexmedetomidine (Precedex) with MAC?

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A
  • decrease MAC by decreasing central nervous system catecholamines and by hyperpolarization of CNS cell membranes
23
Q

beta-blockers, CCB, adenosine with MAC?

24
Q

what PaO2 and MAP could decrease MAC?

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A

PaO2 < 38 mmHg
MAP < 40 mmHg

cardiopulmonary bypass also decreases MAC

25
factors that increase MAC
* Red hair o Increased MAC due to excess pheomelanin production – 19%* * Drug induced increases in CNS catecholamine levels o Cocaine, ketamine, amphetamines * Hyperthermia * Hypernatremia
26
factors that do not alter MAC
* Gender * Duration of anesthesia - *isoflurane decreases * Body mass * Arterial PaO2>38 mm Hg * Arterial PaCO2 15-95 mm Hg * Hematocrit > 10% * MAP > 40 mm Hg Note: Chronic alcohol abuse
27
Loss of consciousness and the immobility (MAC) are not....
“a single continuum of increasing anesthetic depth but rather two separate phenomena.”
28
MAC-awake definition
The average of the concentrations immediately above and below those permitting voluntary response to command.
29
MAC-awake for des, iso, sevo?
1/3 of MAC
30
MAC-awake for halothane?
more than 50% of MAC
31
MAC-awake for Nitrous oxide
more than 60% of MAC
32
MAC-Awake / MAC is important. o The higher the ratio.....
the seemingly faster the recovery*. o The higher the ratio, the poorer the amnestic value.
33
MACAwake * Low dose opioids (2-3 mcg/kg of fentanyl) affects?
minimally affects MAC awake o However, it does bring MAC down so the ratio of MAC awake / MAC becomes higher, and awakening should be more quickly.
34
Esophageal sphincter and MAC-awake?
* MAC-Awake does not ensure return of esophageal sphincter tone or return of pharyngeal function (airway protection). * Concentrations of inhaled agent may require levels of less than 0.1 MAC for patient safety * Sphincter tone is impaired even at very low concentrations – lower than MACawake.
35
MAC-TE
* To allow tracheal stimulation: o No coughing or bucking during suctioning of pharynx o No movement or coughing within 1 minute of extubation o No breathholding or laryngospasm after extubation * MACTE is equal to or exceeds MAC.
36
MAC-Bar
* Minimum alveolar concentration that blocks autonomic responses to surgical stimulus.
37
drugs that decrease MAC
opioid (synergistic) benzos (dose-depenedent) barbs & propofol lidocaine IV nitrous oxide alpha 2 agonists - clonidine & precedex some beta blockers CCB adenosine
38
MAC-awake is higher or lower than MAC?
* MACAwake usually exceeds MACamnesia
39
MAC-awake is affected by?
age (decreases) and inhalation agent o The ratio of MAC awake / MAC is not affected by age as both decrease
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