Provided by Dr. Nuttapol Rittayamai
A 59 years old man presented with COVID-19 pneumonia and severe ARDS. He was ventilated, heavily sedated and paralyzed, and received prone positioning for two consecutive weeks. After discontinuing cisatracurium, he developed asynchrony with the mode Pressure Regulated Volume Control (PRVC). We decided to put an EAdi catheter to evaluate his neural drive and to promote synchronization using the mode Neurally Adjusted Ventilatory Assist (NAVA). Interestingly, his EAdi was very high (varying from60-80 uV) even when receiving high doses of midazolam, fentanyl, and thiopental because of his agitation. His arterial blood gas did not show significant acidosis or CO2 retention to explain such a high EAdi.
Airway pressure delivered was limited during NAVA mode to avoid too high pressure support due to high level of EAdi (Figure 1 – square airway pressure waveform). We thought that NAVA was not a good mode of choice in this case then, to promote weaning, we decided to switch him to PSV mode and gradually decreased the level of pressure support (PS) regardless of the absolute EAdi value (Figure 2).
We found a slight increase in EAdi after switching from NAVA to PSV (Figure 3), however, his breathing pattern was stable. We collected data on P0.1 in both modes, but due to the questionable reliability of P0.1 to represent respiratory drive during NAVA (because the trigger is neurally based rather than flow or pressure), we provide the P0.1 trend during PSV (Figure 4).
Pmusc index (PMI), the pressure generated by the inspiratory muscles which represents inspiratory effort during PSV and calculated as occlusion plateau pressure minus airway pressure before occlusion, was measured at PS of 16 and 8 cmH2O and we found no difference in PMI between the two levels of PS (6 and 7 cmH2O, respectively) (Figure 5 and 6).
Finally, because of the acceptable level of PMI, the ventilator was successfully disconnected and high-flow oxygen via tracheostomy mask was applied after 4 days of weaning with PSV, despite an excessive level of EAdi.
For more information on PMI measurements please see our previous post here.
Further Reading on PMI
Foti G, Cereda M, Banfi G, Pelosi P, Fumagalli R, Pesenti A. End-inspiratory airway occlusion: a method to assess the pressure developed by inspiratory muscles in patients with acute lung injury undergoing pressure support. Am J Respir Crit Care Med. 1997;156(4 Pt 1):1210-1216.