SAAS Module Review Flashcards
What does capnography measure?
Capnography gives feedback about what three parameters/key body systems?
- The partial pressure of C02 in expired respiration
- Capnography provides instantaneous information about:
ventilation (how effectively CO2 is being eliminated by the lungs)
perfusion (how effectively CO2 is being transported through the vascular system)
metabolism (how effectively CO2 is being produced by cellular metabolism).[2]
EtCO2 refers to what? What is the normal value for an adult? How about for children?
- It refers to end tidal C02 (End of breath partial pressure of C02)
- 36-40 mmHg in a healthy adult and the range for children is not significantly different
PaCO2 refers to what? What is the normal value?
PaCO2 refers to the Partial pressure of CO2 in the arterial blood (it is generally 3-5 mmHg higher than EtCO2) and normally in the range 35-45 mm Hg.
Capnogram is what?
a plot of EtCO2 over time
Capnography reads or estimates pac02?
Estimates.
Prediction of PaCO2 from ETCO2 is variable (the major limiting factors = blood flow to the lungs and mismatch between ventilation and perfusion);
ETCO2 may however, also be misleadingly in different conditions where a significant mismatch between ventilation and perfusion exists.
How does infrared light detect the etc02?
Infrared is only absorbed by gases that have two or more different atoms.
Because H20 contains two of the same atoms, it does not absorb infrared.
Because c02 has a carbon, and an oxygen molecule…it does absorb infrared.
The capnography device takes a sample of expired air and aspirates it. The infrared light absorbed is measured, to obtain a partial pressure ETc02.
The normal waveform for capnography, would look like what?
An elephant under a blanket. Basically like a big square.
isoelectric line as exhalation begins, and dead space is cleared from the airway. And then a sharp uptick on expiration (dead space gases are mixed with alveolar gases filled with c02). This expiration plateus (the straight line at the top of the square. Peaks and then drops as inhalation begins, making a line drop downwards completing the square.
During resuscitation, why is ETc02 a good reflection of perfusion status in isolation?
During cardiac arrest alveolar ventilation and metabolism are essentially constant. (the amount of c02 produced and the amount of c02 expired)
EtCO2 therefore predominately reflects pulmonary blood flow. Therefore, EtCO2 can be used as a non-invasive gauge of the effectiveness of cardiac compressions. As effective CPR leads to a higher cardiac output, EtCO2 will rise, reflecting the increase in perfusion.
Good compressions cause ETC02 to go up or down?
ETC02 would go up. There is more c02 because
better perfusion -> Better pulmonary blood flow -> more waste products expired in air -> increased ETc02.
Conversely.
Poorer perfusion -> less pulmonary blood flow -> less c02 expired -> lower ETc02.
If a patient gets ROSC, how would this reflect in ETC02?
How can this be used to predict ROSC?
- A massive rise in c02, because the c02 accumulated during arrest is being expelled . THis is because CO is now restored (heart is beating).
- Before ROSC you may see an increase in ETc02 waveform, as CO is being restored.
What is a key value of capnography as it pertains to compressions?
It eliminates the need to stop chest compressions to check for pulses. Because you can see a rise in ETc02, and hence know that CO is increasing.
Pulse checks should only be performed when a perfusing rhythm has been detected, and in conjunction with a notable rise in waveform capnography suggestive of ROSC. either way the 2 minute cycle of CPR should be completed
Is ETc02 good for checking ventilation rate in cardiac arrest?
ARC: “During a cardiac arrest, the EtCO2 value (ie in mmHg) should NOT be used as a guide for ventilation, and clinicians should be wary about using it to guide ventilation in the immediate post resuscitation phase”
Low CO2 in expired breath from a patient under CPR may imply:
- inadequate cardiac compression or excessive ventilation or both
- a treatable condition (reversible causes)
Hypoventilating a patient would cause ETc02 to do what?
It would rise. Because there is less expired air, and hence C02 will be at a greater concentration IF cardiac output is relatively stable
Hyperventilation would cause ETc02 to drop. c02 is being expired excessively.
The CO2 waveform is analysed for five characteristics?
Height – which depends on the end-tidal CO2 value
Frequency – which depends on the respiratory rate
Rhythm – which depends on the state of the respiratory centre or on the function of the person ventilating (in hospital this would be the ventilator)
Baseline – which should be zero
Shape – there is only one normal shape
What is the advantage of capnography over oximetry?
ETC02 can pick up occlusion of airway, hypoxia, apnoea well before haemoglobin desaturation occurs. It is a leading indicator of hypoxia compared to sp02.
When do you need to use a filter with capnography?
In patients > 40 kg. It effects the readings of paediatrics if you use a filter.
If you observe an increase in ETC02 whilst CPR, indicating potential rosc, increase in CO…what action should you take?
Early indication of ROSC - complete 2 minute cycle but have high index of suspicion on a
pulse will be present; withhold CA drugs (if due) until next pulse check; manage post ROSC as
per CPG
For intraosseous administratin what size flush for adults and children?
adults - 10 ml syringe
paeds - 2-5 ml
