by Francesco Mojoli, Marco Pozzi, Anita Orlando, Isabella M.
Bianchi, Eric Arisi, Giorgio A. Iotti, Antonio Braschi and Laurent Brochard
Critical Care volume 26,
Article number: 32 (2022)
Background
Whether respiratory efforts and their timing can be reliably
detected during pressure support ventilation using standard ventilator
waveforms is unclear. This would give the opportunity to assess and improve
patient–ventilator interaction without the need of special equipment.
Methods
In 16 patients under invasive pressure support ventilation,
flow and pressure waveforms were obtained from proximal sensors and analyzed by
three trained physicians and one resident to assess patient’s spontaneous
activity. A systematic method (the waveform method) based on explicit rules was
adopted. Esophageal pressure tracings were analyzed independently and used as
reference. Breaths were classified as assisted or auto-triggered,
double-triggered or ineffective. For assisted breaths, trigger delay, early and
late cycling (minor asynchronies) were diagnosed. The percentage of breaths
with major asynchronies (asynchrony index) and total asynchrony time were
computed.
Results
Out of 4426 analyzed breaths, 94.1% (70.4–99.4) were
assisted, 0.0% (0.0–0.2) auto-triggered and 5.8% (0.4–29.6) ineffective.
Asynchrony index was 5.9% (0.6–29.6). Total asynchrony time represented 22.4%
(16.3–30.1) of recording time and was mainly due to minor asynchronies.
Applying the waveform method resulted in an inter-operator agreement of 0.99
(0.98–0.99); 99.5% of efforts were detected on waveforms and agreement with the
reference in detecting major asynchronies was 0.99 (0.98–0.99). Timing of
respiratory efforts was accurately detected on waveforms: AUC for trigger
delay, cycling delay and early cycling was 0.865 (0.853–0.876), 0.903
(0.892–0.914) and 0.983 (0.970–0.991), respectively.
Conclusions
Ventilator waveforms can be used alone to reliably assess
patient’s spontaneous activity and patient–ventilator interaction provided that
a systematic method is adopted.
