Figure 1:


a) Give a cause for the abnormality seen in the expiratory phase of the waveforms in figure 1.

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College Answer

a) Either of the following answers acceptable 
• Water in circuit 
• Secretions in trachea or circuit 



This is a pattern recognition question which relies on the candidate's familiarity with troubleshooting equipment. Unfortunately, the college has removed the images, so nobody can recognise the patterns, but we've all seen this, surely. 

The expiratory waveform which is described in (a) probably looks like this, and represents the bubbling of fluid in the airway or in the ventilator circuit.

The picture I used to replace Figure 1 is duplicated from an excellent paper by Correger et al, which actually summarises all sorts of useful ventilator waveform patterns. It is an important resource.



Correger, E., et al. "Interpretation of ventilator curves in patients with acute respiratory failure." Medicina Intensiva (English Edition) 36.4 (2012): 294-306.