This patient is receiving noninvasive ventilation with pressure support. What does the spike at the beginning of inspiration on both the pressure and flow waveforms mean?
Answer: There is an overshoot of both pressure and flow at the beginning of the mechanical breath.
The inspiratory pressure (15 cmH2O) is higher than the set pressure (PS 10 cmH2O + PEEP 4 cmH2O = 14 cmH2O). The cause of this is usually too short a pressure ramp. The problem occurs mainly in patients with decreased compliance and is unusual in patients with increased resistance.
Pressure overshoot may be uncomfortable for the patient in NIV.
In addition, flow overshoot disturbs cycling as it increases the peak inspiratory flow.
Therefore, when pressure and flow overshoots are noted on the waveforms, the pressure ramp should be prolonged.
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