Waveform capnography

Question 1

What is CO2 produced from?

Answer 1

As a waste product of metabolism. 400L/day are produced.

Question 2

How do we get rid of CO2 from the body?

Answer 2

It is carried primarily in red blood cells and then exhaled from the lungs and also .

Question 3

What is the usual concentration (partial pressure) of CO2 in arterial blood?

Answer 3

4.7 - 6.0 kPa

Question 4

What is the most useful measure of CO2 concentration during a cardiac arrest?

Answer 4

End tidal CO2

Question 5

What is end-tidal PCO2 ?

Answer 5

It is the partial pressure of CO2 at the end of an exhaled breath

Question 6

What does end-tidal PCO2 reflect?

Answer 6

It reflects cardiac output and pulmonary blood flow.

Question 7

During a cardiac arrest what happens to someones end-tidal CO2?

Answer 7

During CPR it is low, reflecting the low cardiac output generated by chest compressions.

Question 8

What is used to measure end-tidal CO2 during a cardiac arrest?

Answer 8

Waveform capnography

Question 9

What does waveform capnography most reliably work in ?

Answer 9

People with a tracheal tube

Question 10

Can you use waveform capnography in someone with a SGA or bag-mask ?

Answer 10

yes - but the SGA usually needs a good seal. Bag-mask even less reliable.

Question 11

List the different roles of the use of waveform capnography during CPR

Answer 11

• Confirming tracheal tube placement
• Monitoring ventilation rate in CPR
• Monitoring quality of compressions - better quality CPR will have a higher end-tidal CO2
• Identifying ROSC
• Prognostication during CPR - higher end-tidal CO2 is associated with higher rates of ROSC and survival

Question 12

Regarding waveform capnography what indicates possible ROSC?

Answer 12

A sudden increase in end-tidal CO2.

Question 13

What is a capnograph?

Answer 13

A device which displays a waveform of the concentration of CO2 as it varies during expiration and a numerical value. This is referred to as waveform capnography.

Add photo of waveform capnography

Question 14

How do most capnographs/monitors carrying out sampling work ?

Answer 14

They use side-stream sampling. A T-piece connector is placed in the breathing system, usually on the end of the tracheal tube or supraglottic airway device via a small port on the side which a fine bore sampling tube is connected.

A continuous sample of gas is aspirated and analysed.

Question 15

Describe the image of a standard waveform capnography i.e. what each of the follow represent:
* A-B
* B-C
* C-D
* D
* D-E

Answer 15

• A-B = the baseline, indicating the end of inspiration. In effect the concentration of CO2 in the air (which is virtually zero) or whatever gas is being delivered to the patient.
• B-C = start of expiration, a rapid rise in expired CO2 is seen. Initially no CO2 is seen due to the expired gas coming from the anatomical dead space i.e. volume of respiratory tract which does not take place in gas exchange (larynx,trachea and bronchi). As gas from the alveoli starts to be expired it mixes and CO2 concentration rises.
• C-D = Eventually alveolar plateau is reached. It represents the alveoli taking part in gas exchange. The slight gradual increase during this phase is because not all alveoli empty at the same rate.
• D = at the end of expiration (end-tidal CO2), when CO2 concentration is maximal. In healthy patients this is usually 4.8kPa.
• D-E = start of inspiration, air containing no CO2 is mixed with a small amount of residual gas, this rapidly dilutes the gas until there is no gas containing CO2 being inspired.

Question 16

What is often the first indicator of ROSC?

Answer 16

Rapid rise in end-tidal CO2. This often precedes a palpable pulse.

Add photo example of this.

Question 17

Failure to achieve an end-tidal CO2 of what after 20mins of CPR is associated with poor outcomes?

Answer 17

Failure to achieve an end-tidal CO2 of > 1.33kPa.