1 - 5 Physiology SBAs for the Primary FRCA
Question 1
You have intubated a 54 year old woman who has suffered a cardiac arrest on the ward. CPR is ongoing and you decide to assess her monitoring and arterial blood gas analysis.
Which of the following are you most likely to see?
- ETCO2 0.9 kPa
- pH 7.44
- NIBP 77/45
- Magnesium 0.44 mmol per litre
- Bicarbonate 22 mmol per litre
Answer
- ETCO2 0.9 kPa
End tidal CO2 is a measure of how effectively the lungs are being both ventilated and perfused. In cardiac arrest, even with good CPR, there is very poor perfusion of the lungs, resulting in a low end tidal CO2.
There should, however, still be some CO2, with a reliable ETCO2 waveform on the monitor - if not you need to check whether your tracheal tube is in the right place.
The patient is likely to be acidotic with a low bicarbonate, and the blood pressure will be unrecordably low (unless exceptionally effective CPR is in progress)
You are unlikely to be looking at magnesium on a monitor or blood gas, or in a cardiac arrest situation.