Selection criteria for valid Chartis measurements to calculate the optimal VT20 threshold

1.Presence of positive flow prior to start of assessment.
2.The flow should be consistent.
• This flow may be decreasing over the course of the assessment, but there should be no extended duration of missing flow. This indicates proper catheter balloon positioning and sealing of the airways and that the catheter has not been clogged.
• There should be no sudden increases in flow to a much higher level. This could indicate that the catheter balloon seal was lost.
• During the assessment, if there is an instantaneous loss or drop in flow within the first 30 s and flow does not resume, the assessment should be abandoned and a new one should be re-initiated.
3.At the end of the assessment, the total volume of air exhaled by the patient during the assessment should have been >50 mL.