Monday, May 11, 2009

Waveform of the week: Flow Mismatch

Flow Mismatch as evidence by the scooping in the pressure waveform, a indication of inappropriate inspiratory flow to meet patient demands.

Flow Mismatch

Flow mismatch happens during volume ventilation (VC-CMV or VC-IMV) as a patients respiratory drive increases the fixed/set flow rate does not provide enough assist for the patients demands.
Flow mismatch is easy to identify by recognizing pressure scooping in the pressure waveform. Additionally, the practitioner can evaluate P0.1 to quantify excessive effort.
To correct or prevent flow mismatch the operator can simply adjust the flow rate to match patient demands. However, spontaneous decreases in ventilatory demand will result in unnecessarily higher than average ventilator assist which may result in respiratory muscle disuse, a lower PaCO2 set-point, and delay weaning.
Other actions include; switching from a constant flow pattern to a decelerating flow pattern
, this provides a high initial peak flow, which provides lower peak airway pressures, improved gas exchange, and less patient work.
The operator may also switch to an "Adaptive Pressure Control" mode, pressure control (PC-CMV, PC-IMV) , knowledge based control, or to "Proportional Assist Ventilation".
Lastly, consider increasing sedation if patient demand & or tidal volume exceed clinical goals.


Flow Mismatch: Patient ventilator asynchrony associated with volume ventilation

What the heck is P0.1?

Obtaining P0.1 on various ventilators