Abstract
BackgroundWhether 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.MethodsIn 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.ResultsOut 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.ConclusionsVentilator waveforms can be used alone to reliably assess patient’s spontaneous activity and patient–ventilator interaction provided that a systematic method is adopted.
Highlights
Whether respiratory efforts and their timing can be reliably detected during pressure support ventilation using standard ventilator waveforms is unclear
Ventilator waveform interpretation was originally described in the 90 s’ to assess patient–ventilator interaction [5, 10] and it was proposed as a skill that intensivists should possess in the era of mechanical ventilators displaying real-time waveforms [11]
Materials and methods In this prospective observational study, we enrolled mechanically ventilated patients in pressure support ventilation (PSV) mode with an esophageal balloon already inserted for clinical purposes, either because they displayed any form of asynchrony on the ventilator screen visible at the bedside or they were considered by clinicians to be uncomfortable from a ventilation standpoint
Summary
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. No data are available about waveform detection of minor asynchronies such as trigger delay, early and late cycling These “minor” asynchronies predispose to and are more frequent than “major” asynchronies [5, 8, 14, 15], accounting for more than 75% of the total asynchrony time in patients under pressure support ventilation [16]. Prerequisite for the detection of minor asynchronies is the ability to precisely identify the start and the end of patient’s spontaneous respiratory effort
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