Outline four (4) causes for the capnograph trace (shown below) obtained from a critically ill patient.
a) Ventilator disconnection
b) Esophageal intubation
c) Cardiac / respiratory arrest
d) Apnoea test in a brain dead patient
e) Capnograph obstruction
Though abnormal capnography waveforms are discussed in greater detail elsewhere, there is little discuss here. Either the patient is not producing any CO2, or the CO2 is not making its way to the capnograph.
Reasons for a flat capnograph trace include:
Thompson, John E., and Michael B. Jaffe. "Capnographic waveforms in the mechanically ventilated patient." Respiratory care 50.1 (2005): 100-109.
Babik, Barna, et al. "Effects of respiratory mechanics on the capnogram phases: importance of dynamic compliance of the respiratory system." Crit Care 16 (2012): R177.
Additonally, capnography.com has a series of excellent diagrams and is otherwise an indispenasable resource for this topic.