ET CO2 detection devices

[greg c]

Called in last night to assist with a difficult intubation in which medicine and surgery teams were unable to secure an airway. There was a reluctance to trach given a current medication list including heparin and a IIb/IIIa inhibitor. A retrograde intubation kit was our saving grace and otherwise it is not an eventful story. A learning point did come out of it for the housestaff however, and it might be a learning point to some of you guys as well...

Prior to my arrival, a resident placed the endotracheal tube and pronounced it in place given condensation in the tube as well as a positive CO2 detection device color change. However, the patient's abdomen soon became distended, and sats continued to fall.

So.....

What can cause a false postive color change?
What can cause a false negative?