CO2 Waveforms +Pulse oximetry Flashcards
What does the baseline of the CO2 Waveform represents what phase is it?
Exhalation of anatomic dead space (flat region before it becomes positive)
Phase I
What does the UPSTROKE of the CO2 Waveform represents ? what phase?
Exhalation of anatomic dead space + ALVEOLAR GAS
Phase II
What does the PLATEAU phase of the CO2 waveform represents
Exhalation of Alveolar gas
Phase III
What does the return to baseline, DOWNSTROKE phase of the CO2 waveform represents
Inspiration of fresh gas that DOES NOT CONTAIN CO2
What is CO2?
Carbon dioxide, which is the final product of Aerobic metabolism
Where is End Tidal CO2 measured on the waverform?
End of Plateau phase.
What is ventilation
Process of removing CO2 from the body.
If you’re using a Mapleson circuit, what is the primary cause of an increase in CO2 ?
Inadequate fresh gas flow (no unidirectional valves, no CO2 canisters)
Dead space and CO2
increasing dead space, can increase rebreathing and CO2 retention
Valves and CO2 retention
A stuck open inspiratory valve rebreathing can occur because during expiration, alveolar gas can back fill the inspiratory limb of the circle
A defective expiratory valve can lead to rebreathing of CO2 also because during inspiration, the negative pressure generated by the patient can bring alveolar gas from the expiratory limb of the circuit.
Malfunction of the _______can also cause CO2 rebreathing
CO2 absorber
If the CO2 absorbent malfunction midcase, what do you do?
Increase the Fresh gas flow
Classic rebreathing pattern on the capnography will show
elevation of the waveform baseline that does not return to and HIGHER ETCO2 , PaCO2 may be normal
What is the Capnometer?
Device that measures and displays the concentration of CO2.
What is a Mainstream sampling?
INSIDE the tracheal tube with all inhaled and exhaled gas.
Advantage of mainstream sampling vs sidestream sampling
ADV: response time is faster
DIS: bulkiness of the device, need to be heated to 40C –> risk of burning patient skin, INCREASE DEAD SPACE
Most common sampling method? What does it require?
Sidestream ; Water trap to prevent contamination
What is the average sampling flow rate?
150-250 ml/min
If less than 150, too slow
if > 250, may be contaminated with fresh gas
What is use to deal with water condensation?
Water trap systems
CO2 measurements done by
MASS Spectometry
Mass spectometry work by
separating gases and vapors according to difference in their mass-to-charge ratios.
Colorimetric detection consists of a
ph sensitive paper within a chamber place between tracheal tube and ventilation device.
Yellow ETCO2>15
CO2 measures 3 vital parameters which are
Metabolism
Circulation
Ventilation
Normal ETCO2
35-45 mmHg
The ALPHA angle is between phases
II and III
What is a normal alpha angle ?
between 100-110
What conditions are associated with ALPHA angle greater than 110 degrees?
Obstructive lung disease
Bronchospasm
Kinked ET tube
The BETA angle is between phases
III and IV
What is a normal Beta angle?
Less than 100 degrees
What conditions are associated with INCREASED Beta angle?
Rebreathing SPECIFIC to FAULTY UNIDIRECTIONAL VALVES
What are the characteristics of the CO2 waveform for a patient with COPD?
Longer expiratory time
Capnogram with more rounded appearance
Upward slope of the alveolar space.
When CO2 absorbent is exhausted what happens
Baseline CO2 is increased but BETA ANGLE STAY THE SAME
What is the normal PaCO2 to ETCO2 gradient?
2-5mmHg.
Changes in ETCO2 are usually caused by
Changes in CO2 production
Impaired pulmonary perfusion
Impaired ventilation
Causes of Increased ETCO2
increased production of CO2 delivery of CO2 to the lungs (Increased BMR)
Increased Alveolar ventilation
Causes of Decreased ETCO2
decreased production of CO2 delivery of CO2 to the lungs (decreased BMR)
Decreased Alveolar ventilation
Pulse Oximetry involves the measurement of
oxyhemoglobin concentration
Pulse Oximetry is based on this law.
Lambert-Beer law
SPO2 is measured using
a pulse to estimate SaO2
Pulse oximetry measure 2 wavelengths of light:
Oxygenated blood better absorbs near-infrared light (940nm)
DEOXYGENATED blood better absorbs Red light.
What does the pulse oximetry look at?
the ratio of light during the peak of the waveform relative to the trough of the waveform
During the peak of the waveform, what is the relationship of arterial blood to venous?
the ratio of arterial blood to venous blood is increased.
What does the Lambert-Beer law relates?
Intensity of light transmitted through a solution and the concentration of the solute inside the solution (solute:hemoglobin, solution : Blood)
What is the formula for SPO2
Oxygenated Hgb / Oxygenated Hgb + Deoxygenated Hgb x 100%
Better monitoring with probes placed
closer to central circulation
Associated with FAST SPO2 reading
Ear, Nose, tongue, esophagus, Forehead
Associated with medium SPO2 reading
Finger
Slow SPO2 reading on
Toes
Producing a large and consistent spurious decrease in SPO2?
Injection of methylene blue
Pulse ox read 80% what is the PaO2 approximately
50
SPO2 70, 80, 90 Corresponds to PaO2 of ___, ___, and ____respectively
40,50,60
SPO2 best at monitoring
Vascular compression
Is the pulse ox a monitor of Anemia
No
Is the pulse ox a monitor of ventilation why or why not?
No
Because patient may be HYPERCABNIC and still have a SPO2 100%
is the pulse ox a measure of Bronchial intubation
no
Blue nail polish
May reduce SPO2 reading
The most common method of exhaled gas analysis in the OR
Infrared absorption
