10. Capnography Flashcards by Kira Harms

EtCO2

[CO2] expired gas

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how is EtCO2 measure

exhaled gas analyzer (capnograph)

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PaCO2

[CO2] in arteries
(slightly higher than EtCO2)

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how is PaCO2 measured

arterial blood gas lab

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PaCO2 vs EtCO2

PaCO2 is 3-5 mmHg higher than EtCO2

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PaCO2 and EtCO2 normal relationship

proportional

incr PaCO2 = incr EtCO2

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when can PaCO2 and EtCO2 be inversely proportional

drop in CO
or
low BP

PaCO2 incr
EtCO2 decr

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capnograph

exhaled gas analyzer

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capnograph measures

end tidal CO2
end tidal agent concentration
respiratory rate

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water trap

can get overfilled w/condensation

weird end tidal readings = time to change or dump out

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sample line occluded reading means

time to replace water trap
or
aspirate water with syringe

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GA capnography

tubing hooks to anesthesia circuit

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MAC capnography

tubing placed inside breathing mask

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MAC capnography w/nasal cannula

special cannula w/capnograph line attached

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Low CO/ Low BP

incr PaCO2
decr EtCO2

less CO2 taken to alveoli to be exhaled = more CO2 in blood

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treatment for hypotension

bolus (20mg) of Ephedrine

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EtCO2 is so powerful at telling us

whether or not hypotension is serious enough to compromised perfusion

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hypotension accuracy can be verified by

EtCO2

if EtCO2 is low, then likely that BP is also low and tissue perfusion has decreased

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low EtCO2 and Low BP indicates

perfusion has decreased

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physiologic effects of hypercarbia (hypercapnia)

respiratory acidosis
central pulmonary vasoconstriction
peripheral/cerebral vasodilation
sympathetic response/catecholamine release
CO2 narcosis
possible death

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respiratory acidosis

pH decrease

incr CO2
incr acid in body (H+)
decr pH

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acidosis can cause

catecholamines dont work
vasopressors dont work
cardiac function depressed

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treatment for acidosis

bicarbonate
incr BP

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central pulmonary vasoconstriction

incr CO2 = pulmonary vasoconstriction = PVR

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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)

1. respiratory alkalosis 2. central/pulmonary vasodilation 3. 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

1. propofol 2. redose paralytic or narcotic 3. incr minute ventilation 4. 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:

1. hyperventilation 2. hypotension/low CO 3. 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