Air embolism detection

[jafo1964]

Amongst the myraid of techniques recommended to detect air embolism during neurosurgery the top few based on sensitivity are
Trans-oesophageal echo
Doppler Ultrasound
Decrease in End Tidal CO2
Increase in End Tidal N2.

How did N2 come into the picture since during preoxygenation we had denitrogenated the patient and we are now ventilating with a gas mixture containing only N2O and O2.
What monitoring device are we using routinely that would pick up N2 in the expired gas - ?? multigas monitor working on Mass spectrometry or Raman effect

I have just lost the picture..............

3 degrees under my belt and so much more unlearnt in anaesthesia

[jafo1964]

Figured this one out
the N2 comes from the air that got embolised

Normally ET N2 is 0
Even a increase of 1 to 3 mm of N2 is extremely sensitive

It is more sensitive than decrease in ETCO2 because several other factors can decrease ETCO2 like
hypothermia
hyperventilation
hypotension

ofcourse you need to be using a multigas monitor