Question 17.1

Outline four (4) causes for the capnograph trace (shown below) obtained from a critically ill patient.

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College Answer

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:

  • Ventilator disconnection
  • Airway obstruction (eg. patient suddenly bit down on the tube)
  • ETT perforation (the end tidal gas is escaping via the hole before it gets to the capnograph)
  • Capnograph disconnection or obstruction
  • Water droplet contamination of capnography module
  • Cardiac / respiratory arrest
  • Apnoea test in a brain dead patient


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, has a series of excellent diagrams and is otherwise an indispenasable resource for this topic.