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Flashcards in Inhalation Agents And MAC Deck (40):

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?



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?



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


What is the 2nd gas effect?

The ability of large volume uptake of a first gas (N2O) to accelerate the rate of rise of alveolar partial pressure of concurrently administered companion gas, speeding induction


What is diffusion hypoxia?

Occurs after N2O stopped
N2O diffuses faster from blood to alveoli, so fast there is more N2O than O2 in alveoli and hypoxemia ensues—>avoid by giving 100% O2 for 5-10 minutes after nitrous stopped
- exaggerated with decreased FRC, pregnancy, obesity and pediatrics


What do all inhaled agents have in common?

- all produce bronchodilation —> decrease airway resistance
- non-flammable
- can trigger MH
- mostly exhaled unchanged by lungs
- inhibit HPV
- decrease mucocilliary clearance
- are fluoridated hydrocarbons—> bad for environment
- use lower FGF to avoid overuse
- potentiate non-depolarize get NMB agents


What are the non-pungent agents?

Nitrous Oxide


How can you remember the rate of rise curves?

Nitrous is the fastest, then des, then sevo, then iso


What are the good things about nitrous oxide?

- good analgesic
- safe in MH
- non-flammable, but a O2 source and supports combustion


What are some negative aspects of nitrous oxide?

- avoid in closed spaces (will expand them )
- diffuses into closed spaces 35 times faster than it can be removed
* long term use—> peripheral neuropathy and megaloblastic anemia (B12)
- inhibits methionine synthesis


What close air spaces will N2O diffuse into?

- ETT cuff
- pneumothorax
- complete bowel obstruction
- inner ear
- pneumocephalus
- air embolism
- intraoccular bubble


What are some facts abut Halothane?

* dose dependent decrease in contractility —> hypotension, and decreased CO (SVR and PVR remain the same)
- blunts reflexive tachycardia with hypotension
* SWEET ODOR (thymol preservative) used with pediatrics—> vagal stimulation cause BRADYCARDIA
- pretreat with atropine
- potent MH trigger
* sensitized heart to catecholamines, dysrhythmogenic
—> use epi with caution
- severely decreased respiratory drive
- halothane hepatitis


Who is at risk for halothane hepatitis?

- Multiple exposures over a short time
- females
- obesity
- avoid in liver disease or repeated exposure in 6 months


What are some things iso and des have in common?

- pungent odor—> irritating to the airways
- when rapidly increasing dose will cause tachycardia


What is true regarding des?

- poorly soluble
- rapid wash in and wash out
- uses special vaporizer, heated and kept at 2 atm


What is true regarding iso?

Risk of Coronary steal syndrome—> normal coronary arteries dilate, stenosis ones don’t—> blood shunted from diseased vessels


What is true regarding sevo?

- non-pungent - pediatrics tolerate high levels
* rapid induction and emergence —> sometimes too rapidly—> delirium in children
- potential nephrotoxicity - avoid in renal failure
- reacts with soda lime to create compound A


What are some facts about compound A?

- nephrotoxic, affects brain and liver
- increased compound A with low FGF, high temp (high agent)
Long cases, dry soda lime
—> keep FGF at least 2l/min when running Sevoflurane


What are some facts about Enflurane?

* It is not a good drug *
- decreases contractility and SVR
- marked respiratory depression
- increases cerebral blood flow and ICP
- decreases renal blood flow
- tonic-clinic muscle action- epileptiform EEG
* avoid with renal failure and seizure disorder *