Flashcards in Inhalation Agents And MAC Deck (40):
What is MAC amnesia?
- concentration that blocks anterograde memory in 50% of awake patients
What is MAC awake?
- 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
* Chronic ETOH abuse-liver already working hard (often unreported)
- drugs that increase CNS catecholamines
- meth, cocaine
What are factors that have no effect on MAC?
- thyroid gland dysfunction
- duration of anesthesia
- 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
- acute ETOH ingestion
- cardio pulmonary bypass
- 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%
- 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?
- 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?
Halo 2.3 (very soluble)
A poorly soluble agent a has a _________ inhalation induction and a ___________ emergence. Why?
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?
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
- 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?
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?
* AVOID USE OF N2O IN THESE INSTANCES *
- ETT cuff
- complete bowel obstruction
- inner ear
- 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
- 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