Inhalation Induction Flashcards
Fi
inspired concentration of volatile agent
Fa
concentration of volatile agent in alveoli (and expiratory tubing)
inhalation induction mechanism
- volatile agent on
- Fi increases
- Fa increases
- agent diffuses into blood
- agent diffuses from blood to brain
- pt asleep when conc in brain is sufficient
how does concentration gradient effect diffusion speed?
the greater the conc gradient from the lungs to blood the faster the diffusion to the blood
T/F diffusion is slow at first and then rapid.
false, rapid at first then slows as the concentration gradients decrease
Fa/Fi ratio
how concentrated the alveoli are compared to machine
why is the Fa/Fi ratio less than one?
b/c blood is always absorbing agent from the lungs
list the volatile agents in order from fastest to slowest for Fa/Fi ration approaching 1
nitrous oxide des sevo iso halo
what does a steep slope on the Fa/Fi curve mean?
Fa is rapidly increasing and leads to faster diffusion and faster induction
why is low blood solubility important?
slower initial diffusion into blood and Fa builts up, rapidly diffuses to brain b/c low blood solubility
high blood solubility
quickly diffuses to blood, slow to the brain bc wants to stay in the blood
If Desflurane has a lower blood gas coefficient than nitrous oxide, why does nitrous oxide have a steeper Fa/Fi curve?
Because N2O is typically used in much higher concentrations
how to speed up inhalational induction
higher % poison
higher FGF rate
decrease circuit volume
agent with lowest blood solubility
how much oxygen does a patient need?
250mL
When do you need to run at least 2L/min?
sevo is used
advantages of low FGF
cost effective
preserves heat and moisture
slows drying of CO2 granules
preserves pt temp
disadvantages of low FGF
slower induction
slower emergence
advantages of high FGF
faster induction
faster emergence
disadvantages of high FGF
expensive
dries out airway
accelerates drying of granules
what are the patient factors that affect the speed of induction?
cardiac output
minute ventilation
FRC
low cardiac output
faster buildup of agent conc in blood
faster buildup of agent conc in lungs
faster induction
high cardiac output
slower buildup of agent conc in blood
slower buildup of agent conc. in lungs
slower induction
T/F low cardiac output quickens the intravenous induction?
false, it slows the intravenous induction (how long it takes to travel to the brain)
higher minute ventilation
alveoli are open longer
deeper breath= more surface area
faster breaths = more gas
low FRC
less space in alveoli
higher conc of agent in lungs
faster induction
***peds pts
high FRC
more space in alveoli
lower conc agent in lungs
slower induction
where do volatile agents go in the body other than the brain?
vessel rich group, fat group, muscle group
what are the vessel rich organs
brain heart liver kidney endocrine glands
what percent of cardiac output do the vessel rich organs get?
75%
clinical implications of vessel rich group
saturate quickly
desaturate quickly
muscle group includes
muscle and skin
how much cardiac output does the muscle group get?
20%
how much cardiac output does the fat group get?
5%
clinical implications of fat group
slow to saturate
slow to desaturate
wake up mechanism
- turn vapor off
- conc in machine and lungs decrease
- agent diffuse from blood to lungs
- conc agent in blood decrease
- diffuse out of tissues (brain) into blood
- conc in fat decreases and blood conc further decrease
- blood and brain conc decrease enough pt wakes
what are the factors that affect wakeup
age (geriatric=longer) amount of agent in fat FGF rate blood solubility of agent minute ventilation (higher=faster) amount of narcotic (more=longer) body temp- hypothermia (longer) cardiac output (low=longer) lung disease/decreased alveolar diffusion (longer) APL valve FRC (low=faster)
when will there be more agent dissolved in fat?
obesity
time surgery time
high conc of agent
if you want your patient to wake up faster do you want your APL valve open or closed?
OPEN
