10. Capnography Flashcards
EtCO2
[CO2] expired gas
how is EtCO2 measure
exhaled gas analyzer (capnograph)
PaCO2
[CO2] in arteries
(slightly higher than EtCO2)
how is PaCO2 measured
arterial blood gas lab
PaCO2 vs EtCO2
PaCO2 is 3-5 mmHg higher than EtCO2
PaCO2 and EtCO2 normal relationship
proportional
incr PaCO2 = incr EtCO2
when can PaCO2 and EtCO2 be inversely proportional
drop in CO
or
low BP
PaCO2 incr
EtCO2 decr
capnograph
exhaled gas analyzer
capnograph measures
end tidal CO2
end tidal agent concentration
respiratory rate
water trap
can get overfilled w/condensation
weird end tidal readings = time to change or dump out
sample line occluded reading means
time to replace water trap
or
aspirate water with syringe
GA capnography
tubing hooks to anesthesia circuit
MAC capnography
tubing placed inside breathing mask
MAC capnography w/nasal cannula
special cannula w/capnograph line attached
Low CO/ Low BP
incr PaCO2
decr EtCO2
less CO2 taken to alveoli to be exhaled = more CO2 in blood
treatment for hypotension
bolus (20mg) of Ephedrine
EtCO2 is so powerful at telling us
whether or not hypotension is serious enough to compromised perfusion
hypotension accuracy can be verified by
EtCO2
if EtCO2 is low, then likely that BP is also low and tissue perfusion has decreased
low EtCO2 and Low BP indicates
perfusion has decreased
physiologic effects of hypercarbia (hypercapnia)
- respiratory acidosis
- central pulmonary vasoconstriction
- peripheral/cerebral vasodilation
- sympathetic response/catecholamine release
- CO2 narcosis
- possible death
respiratory acidosis
pH decrease
incr CO2
incr acid in body (H+)
decr pH
acidosis can cause
catecholamines dont work
vasopressors dont work
cardiac function depressed
treatment for acidosis
bicarbonate
incr BP
central pulmonary vasoconstriction
incr CO2 = pulmonary vasoconstriction = PVR
do not hyperventilate what type of pts
hypotensive pts
hyperventilation decr CO2
pulmonary vasodialtion
do not hypoventilate what type of pts
hypertensive pts
pts in neurosurgery
pts w/head injury
hypoventilation incr CO2
pulmonary vasoconstriction
peripheral/cerebral vasodilation
decr in SVR
incr CBF / incr ICP
incr CO2 = peripheral/cerebral vasodilation
at high levels CO2 can act as a
sedative
what level does CO2 trigger narcosis/suppress respiratory drive
70mmHg
1 MAC = _____ PaCO2
1 MAC = 200 mmHg PaCO2
what level does CO2 become life threatening?
> 120mmHg
test prompt – know what CO2 will do to the vasculature
physiologic effects of hypocarbia (hypocapnia)
- respiratory alkalosis
- central/pulmonary vasodilation
- peripheral/cerebral vasoconstriction
respiratory alklalosis
pH increase
decr CO2
decr acid (H+)
incr pH
alkalosis is associated with
neuromuscular irritability
seizures
central (pulmonary) vasodialtion
decr CO2 causes pulmonary vasodilation and decr PVR
hyperventilation causes
decr CO2
hyperventilation is beneficial for what pts
pt w/history of pulmonary hypertension
peripheral vasoconstriction causes
incr SVR
decr CBF
pts we should not hyperventilate
hypotensive pts
hypotension and hypocarbia is bad for cerebral perfusion
most reliable confirmation of correct ETT placement
EtCO2
secondary confirmation signs of ETT placement
breath sounds
chest rise
secondary indication that tube is incorrectly placed
drop in SpO2
if an ETT is placed in esophagus, what will the EtCO2 read
low
might be above 0 due to pt swallowing expired air
after 1st minute of apnea, PaCO2 increases by
6mmHg
after each subsequent minute of apnea, PaCO2 increases by
3-4 mmHg
when during the breath does EtCO2 return to baseline?
during inspiration
when during the breath is EtCO2 at its peak?
expiration
curare cleft
pt is trying to breath over the vent
pt is making spontaneous respiratory efforts
MR could be wearing off
treatments for curare cleft
- propofol
- redose paralytic or narcotic
- incr minute ventilation
- turn off vent for SV
how does propofol treat a curare cleft?
short term solution
suppress respiratory drive
how do paralytics treat curare cleft?
longer term solution
good if surgery has a while to go
re-dosing = less than initial paralysis dose
re-dose roc for curare cleft
1-2mL
how do narcotics treat curare cleft?
longer term solution
suppress resp drive
better if surgery is closer to being done
how does increasing minute ventilation treat curare cleft?
lowers EtCO2
less drive to breathe
when should you turn off the vent to treat curare cleft?
if the case is near the end
if we dont know cause of cleft
2 causes of curare cleft
surgical manipulation
(surgeon pushing on chest)
or
pt breathing over vent
1st step if pt is bucking on vent
turn vent off
then treat w/paralytic, fent, propofol, volatile agent
COPD waveform
upsloping
shows prolonged exhalation times
esophageal intubation waveform
small CO2 waves that disappear within a few breaths
Causes of Hypocapnia reading on EtCO2:
- hyperventilation
- hypotension/low CO
- loose circuit connection
low EtCO2 in Low BP/CO pts
false hypocapnia reading
low CO =
high PaCO2
presents as low EtCO2 because body cannot exhale as much CO2 in low CO states
cardiogenic oscillations at end of expiration
cause by heart contractions displacing air from alveoli
caridogenic oscillations are typically seen with
low respiratory rates
go away as pt starts breathing faster/deeper
if cardiogenic oscilaltions persist
lighten anesthetic
if waveform baseline is increased
CO2 absorbant is exhausted
how do you manage a case with exhausted CO2 if you cant change it out immediately?
increase FGF to 5L/min
if you see humps in waveform expiration prior to the peak what does that indicate?
loose capnograph tubing
how does a sample line become occluded?
full water trap
capnograph tubing pinched
stage II capnograph indication
erratic breathing pattern
what if you see a small hump during inspiration phase of capnograph waveform?
pt is inhaling CO2 during inspiration
causes of CO2 rebreathing?
mapleson circuit
faulty expiratory valve
CO2 reading during sedation
is not accurate
value of capnography during sedation
respiratory rate
immediate apnea diagnosis
why is capnography better than SpO2?
capnography diagnoses apnea immediately
SpO2 cant diagnose until pt is hypoxic
in hypoxia, SaO2 is ______ than what SpO2 reads.
lower
larger humps on sedation capnograph indicates
pt is closer to waking up
smaller humps on sedation capnograph indicates
pt is oversedated
treat w/chin lift/jaw thrust