Patient-Ventilator Asynchrony and Standard Waveforms: Looks Can Be Deceiving

To the Editor:

In a recent issue of Respiratory Care, Ramirez et al¹ assessed clinicians' ability to detect patient-ventilator asynchrony using standard ventilator waveforms. I applaud their contribution. The ability to interpret ventilator waveforms is essential for safe and effective ventilator management. The authors effectively articulate the importance of identifying and minimizing patient-ventilator asynchrony. The purpose of this letter is not to criticize the contribution of Ramirez et al,¹ but rather to take the opportunity to call attention to the fact that in terms of patient-ventilator asynchrony, standard ventilator waveforms can be quite deceiving. Indeed, marked patient-ventilator asynchrony can be accompanied by satisfactory waveforms. A more complete patient-ventilator synchrony assessment requires the addition of diaphragmatic electromyogram waveforms.² Figure 1 shows the standard pressure, flow, and volume versus time waveforms in a patient with severe COPD. The standard waveforms do not indicate any significant asynchrony. However, when you superimpose the diaphragmatic electromyogram tracing over the pressure versus time waveform, marked inspiratory trigger asynchrony can be appreciated. In addition, the diaphragmatic electromyogram peak value of 38 μV indicates that the patient is experiencing a fatiguing work load, which is due in some part to imposed work of breathing, a consequence of inspiratory trigger asynchrony. Standard ventilator waveforms without diaphragmatic electromyogram limit the ability of clinicians to detect patient-ventilator asynchrony.

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Fig. 1.

Ventilator waveforms from a patient with severe COPD. The tracings represent pressure (yellow), flow (green), volume (blue), and diaphragmatic electromyogram (Edi, white) versus time. The white vertical line indicates the onset of diaphragmatic electromyogram activity, and the yellow vertical line indicates the onset of ventilator response via flow triggering.

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