ETCO2 Flashcards
The Haldane Effect causes why type of effect on the OHDC?
A left shift
The Bohr effect causes what type of effect on the OHDC?
A right shift
Three things that can cause a left shift of the oxygen-hemoglobin disassociation curve?
- ^ pH
- < 2,3 DPG
- < T
4.
Four things that can cause a right shift
- < pH
- ^ DPG
- ^ Temp
- ^ CO2
How does a left shift affect binding?
The O2 is more tightly bound and less available for cells. The cells get “left behind”.
How does a right shift affect binding?
O2 is less tightly bound and more available for cells. Think, “Right Hand”, O2 is “handed out” more readily
First “fix” for elevated CO2 in an awake patient?
BiPAP.
Provides PEEP and pressure support increasing Vt and Ve since f can’t be adjusted in this patient
What is one cause of divergent PaCO2 and ETCO2 2 levels?
an increase is dead space
How would a PE cause a divergence between between PaCO2 and ETCO2?
By decreasing blood flow to the AC unit which leads to a lack of diffusion of CO2 which leads to a decrease of exhaled CO2 which is what ETCO2 measures. However the CO2 in the blood increases because it cant be diffused to the AC unit and exhaled.
Formula to quantify respiratory deadspace?
PaCO2- PETCO2/ PaCO2
What is the IPI?
Integrated Pulmonary Index
What metrics make up the IPI?
- ETCO2
- Respiratory rate
- SpO2
- Pulse rate
What is the IPI measurement range?
1-10 with 1 being the worst and 10 the best. 8 and above are normal values
What is the first step in cellular respiration?
Glycolysis
What happens during glycolysis?
A 6 carbon glucose molecule gets lysed into two 3 carbon pyruvate molecules.
Does glycolysis require oxygen?
No
After glucose is lysed into pyruvate, what is the next step?
The pyruvate is converted to Acetyl COA, a 2 carbon molecule.
During the conversion of Pyruvate to Acetyl COA, what happens to the free carbon molecule?
It leaves the cell into the blood stream and is carried to the lungs to be exhaled.
What percent of exhaled CO2 comes from pyruvate to Acetyl COA conversion?
About one-third of the carbon dioxide
you exhale comes from the transformation of pyruvate into acetyl CoA
How many carbon molecules does Acetyl COA lose as it enters the Krebs cycle?
Two, which accounts for the other 2/3 of the exhaled carbon.
What percentage of CO2 is dissolved in the blood?
5-10%
How much (as a percent) of C02 is bound to the hemoglobin molecule?
20%
How much CO2 is transported as bicarbonate
75%
What are the two classifications (based on location) of chemoreceptors?
central and peripheral
What anatomical structure detects a rise in CO2 in the blood?
Chemoreceptors
Where is the central chemoreceptor located?
The medulla oblongata and uses CSF to detect changes in pH.
Where are the peripheral chemoreceptors located?
The aortic arch and carotid artery
What metrics do the aortic arch chemoreceptors measure?
CO2 and O2 but not pH
What metric does the central chemoreceptor measure?
pH
What do the carotid artery chemoreceptors measure?
pH, CO2 and O2
What is CO2 narcosis?
When the paCO2 approaches 75mmHg, it causes hypoventilation , worsening hypercarbia and hypoxia.
How is respiratory acidosis addressed?
By increasing Ve
How is respiratory acidosis addressed in the awake patient?
By adding pressure support likely via BiPAP w/PEEP
How does a rising pH effect calcium
It causes calcium to become more bound to albumin, reducing available calcium in the serum
Five causes of blowing off too much CO2?
- O2 issues - trying to breath in more O2 increases Ve and leads to more exhaled CO2
- Psychological- anxiety leading to hyperventilation
- Stimulant drugs 0 leading to hyperventilation
- CNS - Disorders like ^ ICP lead to ^ f
- Excessive Ve from vent or bagging
Causes of not producing enough CO2 (2)?
- Poor perfusion - think about CPR with a low ETCO2
level due to decreased perfusion - Decreased metabolism - hypothermia
What is the normal V/Q ratio?
0.8
How is the normal V/Q ratio derived?
By dividing a Ve of 4L/min. by a CO of 5L/min.
Describe the ‘West’s Lung Zones”?
The lung is divided into three zones, (1)upper, (2)lower and (3) middle with differing V/Q ratios.
The amount of blood flow is subject to graviry
Zone 1 Ventilation > perfusion
Zone 2 best V/Q match
Zone 3 poor perfusion AND ventilation- perfusion is poor r/t hypoxic vasoconstriction
When ventilation stays the same and pulmonary circulation is compromised, the V/Q will ?
increase > 0.8
If perfusion remains constant and ventilation is compromised (shunt), the V/Q will ?
decrease < 0.8.
In terms of measurement levels, how do the ETCO2 and PaCO2 relate?
The PaCO2 will always be higher
What are the phases of caponography?
I, II, III, 0
What does Phase I represent?
Anatomical dead space exhalation. What’s that? We are
exhaling the air in our non-conducting airways that never saw any
gas exchange in the alveoli. This line doesn’t leave baseline even
though it’s exhalation because there is no CO2 in this air (it’s the
same as atmospheric air).
What does Phase II represent?
A mix of anatomical dead space and the alveolar air. This
is a sharp increase in the CO2 value after the anatomical dead
space has mostly been cleared out. Gas mixing is messy, and we’re
seeing the mixing of those gasses live on our waveform here in
Phase II. This phase bleeds into Phase III because it’s always slightly
mixing
What does the Phase III slope on an ETCO2 waveform represent?
- Alveolar gas. Phase III is the best look at alveolar CO2
concentrations that we have (and PaCO2 for that matter)
What does the Alpha angle represent?
The Alpha Angle is the first transition after leaving
baseline. It signals the transition between mostly mixed gas to
mostly alveolar gas
What does the Beta angle represent?
This is the transition from the end of exhalation to
inhalation - it signals a reversal of airflow. The value rapidly drops
because there is no measurable CO2 in the air that the patient is
breathing in.
What does Phase 0 represent?
Room air. As noted above, the room air has no
measurable CO2 in it, so the waveform will return to baseline. This
phase also includes a pause at the end of inhalation, if the patient
has one(
Where on the capnograph waveform is the ETCO2 measured?
At the Beta angle
What can cause a progressive decline in serial waveform amplitudes?
What can cause a progressive increase in serial waveform amplitudes?
What is a cause of Phase I not returning to baseline?
Air trapping
What might a “shark fin” waveform indicate?
Uneven alveolar emptying, (Asthma, bronchoconstriction)
What might a curare cleft indicate?
A patient nor properly sedated, or coming out of sedation.
What might a pigtail sign indicate?
Alveolar collapse?
How might you address the underlying cause of a pigtail capnograph waveform?
Increase alveolar recruitment/expansion (BiPAP, PEEP0
What might a downsloping Phase III indicate?
Emphysema or a pneumothorax
How does emphysema cause a down sloped Phase III
In emphysema, there is lower airway remodeling. It’s like taking an old,
closed-off house, and making it a modern ‘open-concept’ house by
knocking down some walls. That’s cool if you’re redoing your house,
but not so cool for the lungs. The lack of alveolar walls means that gas
exchange occurs rapidly, and CO2 moves down its concentration
gradient prematurely. This creates the reversed Phase 3 by expelling
the most CO2 concentrated gas first, instead of last.
How can a chest tube/pneumothorax cause a downsloping Phase III ?
If airflow going out of the chest tube moves at a higher rate than the
patient’s expiratory flow rate, it can rob the ETCO2 waveform of CO2
as the breath gets slower towards the end of exhalation. This isn’t
necessarily bad, but it’s something you might observe. The CO2 is still
leaving the chest, just in a different direction. This also may clue you
into how much air is actually leaving the chest through that chest
tube.
How would acidosis affect the OHDC?
Causes s rightward shift
What is the SaO2 level?
SaO2 is the percentage of available binding sites on hemoglobin that are bound with
(presumably) oxygen in arterial blood
What is PaO2 and what three things determine it?
PaO2, the partial pressure of oxygen in the arterial blood, is determined solely by
1. the pressure of
inhaled oxygen (the PIO2),
2. the PaCO2, and
3. the architecture of the lungs (V/Q abnormality)
What does the PaO2 indicate?
PaO2 is a sensitive and non-specific indicator of the lungs’ ability to exchange gases with the
atmosphere
