Inhalation Agents And MAC Flashcards
(40 cards)
What is MAC amnesia?
MAC 25%
- concentration that blocks anterograde memory in 50% of awake patients
What is MAC awake?
50% MAC
- Concentration required to prevent eye opening on verbal command
What is MAC intubation?
130% MAC (1.3)
- concentration required to prevent movement or coughing during intubation
What is MAC bar?
150% MAC (1.5)
- concentration required to block adrenergic response to skin incision
What are factors that increase MAC?
- age—> term infant to 6 months of age have the HIGHEST MAC REQUIREMENT
- hyperthermia
- Chronic ETOH abuse-liver already working hard (often unreported)
- hypernatremia
- drugs that increase CNS catecholamines
- meth, cocaine
What are factors that have no effect on MAC?
- thyroid gland dysfunction
- duration of anesthesia
- gender
- hyper or hypokalemia
- hyper or hypocarbia
What factors decrease MAC?
- hypothermia- for every 1 C decrease in body temp, MAC decreases by 2-5%
- pre-op meds (fentanyl, versed, opioids, barbiturates, hypnotics)
- neonates/premature infants
- elderly
- pregnancy
- acute ETOH ingestion
- lithium
- cardio pulmonary bypass
- hyponatremia
- alpha 2 agonists
- calcium channel blockers
- severe hypoxemia: PaO2 <38 mmHg
MAC values of halogenated inhalation agents
- N2O—-> 104%
- Sevo—-> 2.2%
- Iso—-> 1.4%
- Des—-> 6.6%
- Halo—-> 0.75%
- En—-> 1.68%
Which agent should you avoid with severe nausea?
N2O
What is the concentration effect?
High inspired concentration speeds up induction
How does alveolar ventilation affect induction?
Increased alveolar ventilation increases rate of rise of agent and speeds induction
How does the anesthesia system affect induction?
Volume, solubility of components and gas flow rates—> higher rates speed induction
What does uptake from alveolar space depend on?
Depends on:
- solubility
- CO
- alveolar/venous partial pressure difference
If you make a change in your agent and gas flows are low it will take a while to see the effects. What can you do about this?
- either increase flows to speed it up or…
- give IV agent along with it (propofol)
What is the most important single facto in determining the speed of induction and the rate of emergence?
SOLUBILITY
What is solubility?
The amount of agent required to saturate a volume of blood at a given temperature
- expressed as blood:gas partition coefficient
What is true regarding high solubility?
- the more soluble the agent the more it will be take up into pulmonary capillaries and into tissues
- high solubility will have high blood:gas partition coefficient
What are the blood:gas partition coefficients for the halogenated agents?
N2O—-> 0.47 Sevo—-> 0.65 Iso—-> 1.4 Des—-> 0.42 Halo 2.3 (very soluble)
A poorly soluble agent a has a _________ inhalation induction and a ___________ emergence. Why?
Faster, faster
Faster induction—> poorly soluble agent rapidly reaches saturation in blood- is saturated when reaches the brain
Faster emergence —> agents prefer fas state and come out of tissues/blood quicker
How does a high CO affect induction?
Slower rate of rise and slower induction
- blood flowing too fast to be saturated
How does low CO affect induction?
Allows large alveolar partial pressure gradient to from, blood gets maximally saturated
- faster induction
What does a large partial pressure difference do?
Enhances uptake and speeds inhalation induction
What % of body weight and CO do the vessel rich group occupy?
10% of body wt
75% of CO
What is the relative solubility in the fat group compared to the vessel rich group?
20 fat
1 vessel rich
—> will store in fat much longer