Inhalation Anesthetics Flashcards
Apneic threshold
highest blood CO2 level at which a patient can remain apneic
Do anesthetics lower or raise the apneic threshold?
raise, suppresses the drive to breathe
Does pain lower or raise the apneic threshold?
lowers, stimulates breathing
hypoxic drive
lowest oxygen level a patient can no longer remain apneic
normal patient ~60mmHg
for a healthy patient is it hypoxia or hypercarbia that causes them to breathe?
hypercardia
for a patient with lung disease is it hypoxia or hypercarbia that causes them to breathe?
hypoxia
less responsive to increase in CO2
The CNS chemoreceptors respond to changes in what?
PaCO2
The PNS chemoreceptors respond to changes in what?
PaO2
minimum alveolar concentration (MAC)
mac of an exhaled gas that will prevent movement in 50% of patients during incision
A patient is exhaling 0.8 MAC of Des. What is the percentage they’re exhaling?
4.8%
A patient is exhaling 0.3 MAC of Sevo. What is the percentage they’re exhaling?
0.6%
1.2% Des + 30% N2O = _____ MAC
0.2 MAC Des + 0.3 MAC N2O = 0.5 MAC
MAC awake
0.4 MAC
Reliable awareness prevention (with narcotics)
0.8 MAC
Reliable awareness prevention (even without narcotics)
1.0 MAC
50% chance of movement (w/o paralytics)
1.0 MAC
5% chance of movement (w/o paralytics)
1.3% MAC
How to know if patients are aware or not when paralyized
vital signs would be high
What are the two reasons to give volatile agents?
prevent movement
prevent awareness
What are factors that decrease MAC?
1- IV anesthetics 2- Old age (4-6% per decade) 3-ACUTE intoxication 4- pregnancy (progesterone sedative) 5-temperature factors 6- blood factors
What are the 4 blood related factors that decrease MAC?
hypoxia
hypercarbia
hypotension
anemia
What are the factors that increase MAC?
YOUNG HOT SALTY ALCOHOLICS
young
hot (hyperthermia/ burn pt)
salty (hypernatremia)
alcoholics (chronic)
Blood/Gas Partition Coefficients
When you reach equilibrium then it is the % of blood concentrated compared to the lungs
If the agent is soluble in the blood, the blood will have more agent than the lungs at equilibrium and the blood gas coefficient will be lower or higher?
Higher
What are the neurologic effects of Volatile agents (not N2O)?
1-Dilates the cerebral vasculature, increases CBF, increases ICP
2- emergence delirium in kids
3- decrease seizures
4- decrease cerebral metabolic rate of oxygen
What are the cardiac effects of volatile agents?
1-decrease cardiac contractility
2-cause systemic vasodilation
3- cause coronary vasodilation
What are the respiratory effects of volatile agents?
1-rapid, shallow breathing (increase in CO2), lower Vd
2- increase apneic threshold
3- decrease hypoxic drive
4- bronchodilation
Other effects of volatile agents?
1-decreases renal blood flow 2- decreases hepatic blood flow 3- prolongs muscle relaxant 4- PONV 5- MH 6- inhibits "non-shivering thermogenesis" in peds
Nitrous oxide
1-analgesic 2-PONV 3-stimulates sympathetic increases PVR 4-dilates cerebral vasculature 5-seizures less likely 6-supports combustion 7- post op diffusion hypoxia 8- expands air containing cavities 9- increases cerebral metabolic rate of oxygen 10- prolonged exposure bad
What does prolonged exposure to N2O cause?
1-bone marrow depression
2- can inhibit enzymes in DNA synthesis
3-neurological deficiencies
How does Nitrous oxide expand air bubbles?
Nitrous oxide will diffuse into air pocket faster than the nitrogen can diffuse into the blood
What are the contraindications for N2O?
1- facial or throat surgery with laser 2-ophthalmic surgery 3- severe COPD 4- cardiopulmonary bypass surgeries 5- certain abdominal surgeries (laparoscopic, bowel obstruction) 6- inner ear surgery 7- 1st trimester of pregnancy 8- neurosurgery
What are the advantages of iso?
mimimal cardiac depression
causes coronary vasodilation
what are the disadvantages of iso?
pungent odor
associated with coronary steal syndrome
Coronary steal phenomenon?
when iso causes coronary vasodilation the stenotic coronary arteries cannot vasodilate as well as the normal coronary arteries
What are the advantages of sevo?
least pungent
what are the disadvantages of sevo?
potential risk for nephrotoxicity (free fluoride ions & compound A)
What are the effects of compound A thought to be more significant with?
prolonged sevo use
high conc of sevo
low FGF used
desflurane
1- high vapor pressure 2- specialized vaporizer 3- fastest induction and emergence 4- possible sympathetic response 5- pungent
What are the advantages of xenon?
inert
low b:g co
minimal cardiovascular effects
doesnt trigger MH
What are the disadvantages of xenon?
rare and expensive
low potency
