1 - 5 Physiology SBAs for the Primary FRCA

1 - 5 Physiology SBAs for the Primary FRCA
Photo by Unseen Studio / Unsplash

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


  • 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.