This patient is intubated and ventilated using pressure support (PS) mode. Why is the shape of the flow and pressure waveforms abnormal?
Answer: The pressure waveform shows a very steep decrease before the mechanical breath (1). During inspiration, the pressure rises instead of having a square shape (2). Flow during inspiration is rounded instead of having a triangular shape (3), and there is early cycling because of the small distortion of flow at the beginning of expiration (4).
All these abnormalities mean that the patient has a strong inspiratory effort and the ventilator is not providing enough flow. This flow starvation in PS can be corrected by increasing pressure support and shortening the pressure ramp.
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