Ventilator Flashcards
the first ventilators used ____ pressure. They were called _____
negative
the iron lung
The iron lung was developed to save victims of respiratory failure due to
polio
in positive pressure ventilation, the only connection between the patient and the machine is the _____
endotracheal tube
why we call them “agents” and not “gasses?”
administered as vapor, not gas
Vapor
a solution in liquid form dissipates or evaporates and releases molecules into the air around it
Vapor pressure
pressure exerted by a gas above a liquid in a sealed container
Strong intramolecular forces = _____ vapor pressure
lower
Weak intramolecular forces = ____ vapor pressure
higher
Water has ___ vapor pressure
lower
We can smell liquids that have (lower/higher) vapor pressure
higher
ie: acetone
(low/high) vapor pressure liquids easily give up their molecules to evaporation
high
Anesthetic agents have (lo/hi) vapor pressure.
high
Highest vapor pressure amongst anes. agents
Desflurane
We pressurize the agent ____ to ___ atm and heat it to ____ C
Des
2
40C (Barash: 39C)
principle of fluid dynamics that pulls the vapor molecules off the canisters and into the circuit
Bernoulli’s
Venturi Effect
The entrainment of fluid (gas or liquid) due to the drop in pressure
Bernoulli’s principle states that…
An increase in the speed of a fluid occurs simultaneously with a decrease in pressure or a decrease in the fluid’s potential energy
Venturi effect in the machine
(a drop in pressure will entrain gas/liquid)
-fresh gas flows over the top of the canister
-creates a - pressure grdnt
-pulls vapor up and out
why do we reach MAC faster if you turn your flows up at the beginning of the case?
Venturi effect
neg. pressure in vaporizer pulls vapor up and out of canisters
MAC of Desflurane
6.6%
most lipid insoluble of all the agents
Desflurane
lipid insoluble volatile agents
-body trying to push it back out through the lungs
-force it in by high inspired %
(why Desflurane the quickest on and quickest off)
quickest on and quickest off volatile agent
Des
populations is Desflurane good for
Quick cases
obese
Which patients is Desflurane bad for?
Long cases
reactive airways (asthma, smokers)
tachycardia
Desflurane settings
flows max: 1L/min
inspired percentage high: 12%+
will reach MAC in same time as Higher % and flows, minus the SEs
Sevoflurane MAC
1.8%
Most to least lipid sol
Iso
sevo
Des
least pungent of the agents
Sevo
“Sevo smells bessst”
“smell the sevo, it’s great!”
Sevo, sweetie
agent of choice for inhalational inductions
Sevo
b/c she smell gewd
Flow requirements for ____ are 2L/min due to risk of forming _____
Sevo
Compound A
“sevo serving us compound A”
populations is Sevoflurane good for?
Reactive airways
case that requires high flows (bronchs)
LMA (not paralyzed = higher risk of bronchospasm)
most lipid soluble of the agents
Isoflurane
(soluble/insoluble) agents take the longest to go on and to come off
soluble
Higher b:g = slower
Iso (highest b:g) is slowest
(remember, when talking about agents, “in/soluble” means water/blood solubility)
What happens to insoluble agents in the body?
body sequesters it in the fat and then rereleases it into the plasma
MAC of Isoflurane
1.17%
What cases is Isoflurane most suited for
remain intubated and ICU admit
lasts longer = anesthesia “for the road”
most neuroprotective of the agents
Iso
I so save your brain
All agents reduce ___, which is good for the brain, but reduce ___ , which is bad for the brain
cerebral metabolic rate
cerebral blood flow
What makes Iso more neuroprotective?
reduces Cereb metab rate more & blood flow less
(all agents:
reduce CMR= good
reduce CBF = bad)
When to use Iso
hemorrhagic stroke
head trauma w/ crani for hematoma evac
and other pts that always go direct to ICU on vent
basic components of air
21% oxygen
78% nitrogen
and other stuff we dc about rn
inspiring 75% oxygen & four 4.5 % Desflurane
where’s the rest?
We’re giving air (78% Nitrogen)
remaining % = nitrogen
inspired and expired gasses here are measured in
%s
Flows are measured in
L/min
Six percent of 0.5 liters is the same DOSE as ___ percent of 2 liters
six
same percentage, just takes less amount
low-flow anesthesia allows us to use less agent at ____
steady state
Which is more expensive?
TIVA
inhaled agents
TIVA
Which is worse for the environment?
low flow anesthesia
TIVA
low flow anesthesia
primary benefit to low-flow delivery
economic
(earth, you’re second I guess lol)
primary downside of low flow anesthesia
changing dose takes longer
How to best change dose in low-flow anesthesia
temporarily raise your flows
or
inspired % really high or really low
after desired MAC is reached, put settings back how they were
etCO2 capnography
normal range
30-40
NOT 35-45; thats PCO2 (PaCO2) on ABGs
capnography is measured in
pressure mmHg
_____ is about 5 points higher than ____
PaCO2 (listed as PCO2 on ABG)
>
etCO2
T/F
The gap in PCO2 (PaCO2) and etCO2 is due to dead space, especially from the vent circuit.
False
gap exits b/c gases use differences in partial pressures to diffuse (gas exchange)
etCO2 sensor on circuit so close to mouth that dead space is not a significant contributor
T/F
the vent circuit contributes greatly to dead space, which increases the gap between PCO2 and etCO2
False
etCO2 sensor on circuit so close to mouth that dead space is not a significant contributor
T/F
PACO2 measures CO2 in the arteries
False
PACO2 = Alveoli
PaCO2 = arteries
(“Al” both tall; “ar” both short)
PCO2 NR
35-45
(etCO2 30-40)
T/F
PCO2 and etCO2 are interchangeable.
FALSE
PCO2 = PaCO2 =arterial CO2
etCO2 = expired CO2
Our etCO2 is 32. What would we expect the PCO2 to be?
37
etCO2 is usually 5 points lower than PCO2
T/F
PCO2 = PACO2
False
PCO2 a.k.a. PaCO2 = arterial
PACO2 = alveolar
respiratory alkalosis in a long case
kidneys compensate: excrete bicarb
in PACU: metabolic acidosis
compensate by hyperventilating
(hard to do with opioids they’ve been sedated with)
T/F
Dead space can increase gap between PaCO2 and etCO2.
True
but
not the reason it exists
When speaking on gas diffusion, we describe it in terms of _____
partial pressures!!!
The partial pressure gradient is
~5 mmHg
T/F
CO2 crosses alv. Mem using active transport.
False
passive transport/diffusion
How thick is the alv. memb?
0.3 micrometers
Passive transport is also called
diffusion
T/F
Gas exchange occurs when there is an equilibrium.
False
without a sloping gradient, molecules don’t move
Gases move from areas of higher to lower _____
partial pressures
not concentration thats for solids dissolved in liquids
Fick’s Law of Diffusion
directly controls pH
CO2
In pH management, what parameter is easiest for us to control?
CO2
T/F
CO2 is a base.
False
its an acid
Abnormal pHs mostly result in
acidosis
T/F
Pts lose more blood at an acidic pH than at normal pH.
True
clotting cascade slows down
In acidosis, K moves (into/out of) the cell.
acidosis:
K out
H in
How does acidosis lead to hypovolemic shock?
flaccid peripheral vasculature
SVR drops
BP drops
How do shock and acidosis work together to make things 100x worse? lol
Acidosis: flaccid vasculature, SVR & BP drop
shock!
Shock: anaerob. respir8n = lactic acid
worsened acidosis
Normal etcO2 but pt is still trying to breathe
respiratorily compensate for metabolic acidosis
maybe d/t
early hypovol shock (blood loss/inadequate fluid resuscitation)
inspired CO2 should always be
zero
inspired CO2 above 0 means…
CO2 absorbent needs to be changed
T/F
Using low-flow anesthesia will require more frequent changing of CO2 absorbent
True
slower air is more likely to go thru channels in the crystals & wont absorb as well
Channeling
-preferential passage through absorber via pathways of low resistance.
-decreased efficacy
-bypass absorbent granules
Total flows should never be less than….
volume of inspiratory limb
Volume is measured in
mL
Volume waveform measures (inspired/expired) tidal volume.
expired
delta VT
difference between VT and VT-INSP
delta VT is also known as
your leak
T/F
O2 absorbed = CO2 expelled
O2 absorbed > CO2 expelled
troubleshooting a leak (delta VT)
check:
cuff pressure
circuit connections (CO2 sampling line)
An ETT cuff must be ____ to protect against aspiration.
patent
calculation for minute ventilation
RR x Vt = total volume/minute
Minute ventilation
definition
Minute ventilation is measured in
volume/min
L/min
circuit disconnects or vent failures can present early as…
a big leak
Circuit disconnect
break in the system that delivers ventilation and drugs to the patient
accidental extubation can present as a
Circuit disconnect
ETT occlusion will show a _____ alarm
A disconnect will be a ____ alarm
high pressure
leak
You are manually ventilating your pt as you had to disconnect them d/t a leak. Help is on the way. During this time you should administer ____.
propofol
(pt is not receiving any IA at this time)
new to anesthesia, who dis?
pressure waveform
pressure waveform measures …(3)
3 pressures:
peak, plateau, and PEEP
pressure waveform measures in which units?
cm H20
2 modes of ventilation
volume and pressure
Volume mode
choose volume (mL) & rate
delivers volume regardless of pressure
can set a max pressure
normal PEEP (healthy lungs)
0
lungs return to atmospheric pressure on end expiration
pressure mode
set a pressure (cm H2O) & rate
delivers pressure regardless of volume
no max volume setting!
must monitor the pressure yourself
“pressure mode increases the pressure on the CRNA”
Which mode does not allow a max limit for the other parameter?
Volume
pressure
pressure
cannot set max volume
“pressure mode increases the pressure on the CRNA”
volume auto flow
type of volume mode
machine calculates pressure needed to deliver the set volume (for each breath)
accounts for pt’s compliance
consistent vol w/ minimal peak prsr
(volume autoflow mode)
On the pressure waveform, __ & __ are the same.
peak and plateau
T/F
the same pressure can deliver variable volumes
True
(ie before and after insufflating belly)
if a small amount of pressure results in a large change in volume
high/good compliance
lot of pressure to result in just a small expansion of lung volume
low /poor compliance
Which is more common?
obstructive
restrictive
obstructive
pure obstructive
✅ compliance
❌how fast the gases can move through the airways
always worse on expiration
obstructive
examples of obstructive problems
Dz: COPD, OSA, asthma
Fxnl: bronchospasm, laryngospasm, obstruction
How obstructive issues change breathing?
slower, deeper breaths
reduced RR
reduces air lost to dead space
Dead space calc
2cc/kg/breath
or 150 cc/breath for adults
When do we see this?
obstructive capnography (“shark fin”)
asthma, COPD
breathing too fast and your VT is too low
T/F
Obstructive patients need PEEP from the ventilator.
False
have pathologically high auto PEEP
don’t add more
we usually add _____ of PEEP on the vent to prevent atelectasis
2-3
do not add any PEEP to obstructive Dz (ie: COPD)
restrictive processes call for (higher/low/no) PEEP
higher
Restrictive disease is anything that reduces
compliance
no obstruction to slow gases
examples of restrictive disorders
PnA
ARDS
MV w/ pulmonary failure
DO NOT hand-ventilate these patients during transport
restrictive Dz
keeps tighter control of their settings
Changing vent on pt with high PEEP & restrictive Dz
(PEEP 10-15)
when disconnecting,
inflate & clamp
unclamp when on new vent
prevents fluid buildup in RHF and pulm edema pts
Abdominal insufflation
Pregnancy
Trendelenburg position
are examples of…
functionally restrictive
Extrinsic Pulmonary Disease
restrictive Dz treatment
✅ air flow –> increase RR
✅ no significant dead space
reduce Vt (don’t force volume)
PEEP! (so alveoli dont shut –> atelectasis)
do not use auto flow for pts with…
severe restrictive (ARDS, Pna)
use pressure mode for this instead
T/F
emphysema is both restrictive and obstructive.
True
what fun lol
what’s happening?
Patient trying to breathe over the vent
What’s happening?
obstruction
What do you do when this appears?
elevated baseline = change CO2 absorber
Whats happening?
whats happening?
You noticed this waveform, and recognize it as _______. The first step is to _____ and then ____.
esophageal intubation
pull ETT & intubate trachea
decompress stomach w/ OGT
You notice this waveform. Your first step is to _____. If that is working normally, you must ____.
check the CO2 sampling line
replace water trap
A defective water trap can also give you a false low ____.
etCO2
how long do water traps last?
4 weeks
We would to increase expiratory time for _____ diseases, but decrease it for ____ diseases.
increase E time = obstructive (COPD)
decrease E time = restrictive (ARDS, PnA)
compliance equation
change in pleural pressure
We should use ______ mode in pts with restrictive processes
pressure mode (keep their alveoli open; need PEEP)
DO NOT USE volume autoflow
Volume autoflow is indicated for ____ processes
obstructive
obstructive: use slower, deeper breaths (volume; NO extra peep)
T/F
Volume autoflow is good for normal, healthy lungs.
True
Volume autoflow can be seen as…
a gentler version of normal volume mode
(restrictive mode)
What to do and what NOT to do
needs: pressure! (PEEP to keep alveoli open)
do not give: volume
