Performance and applications of bedside visual inspection of airway pressure–time curve profiles for estimating stress index in patients with acute respiratory distress syndrome
To determine the performance of bedside visual inspection of airway pressure-time (Paw–t) curve profiles (VI) for estimating stress index (SI) in patients with acute respiratory distress syndrome (ARDS). A prospective study in 30 subjects with ARDS receiving mechanical ventilation at two peak inspiratory flow (PIF) settings: 60 or 40 L/min. For each study session, two physicians inspected real-time Paw–t waveforms from mechanical ventilator’s monitoring screens at bedside for 30 s and interpreted which of the three patterns (tidal recruitment, noninjurious ventilation or tidal overdistension) the Paw–t curve profile was compatible with. Subsequently, the study was repeated again at the second PIF setting. SI was derived from a standardized dedicated software program and categorized into three groups: SI < 0.9, or tidal recruitment; SI = 0.9–1.05, or noninjurious ventilation; and SI > 1.05, or tidal overdistension. The lower PIF setting increased the sensitivity of VI to correctly estimate SI (75% vs. 50%; p = 0.005). At PIF 40 L/min, the likelihood ratio of a positive test was 3.6, 5.4 or 7 if the Paw–t curve profile was interpreted as noninjurious ventilation, tidal recruitment or tidal overdistension, respectively. The likelihood ratio of a negative test ranged from 0.55 for tidal recruitment to 0.32 and 0.19 for noninjurious ventilation and tidal overdistension, respectively. Experience in mechanical ventilation did not influence the accuracy. Bedside VI is moderately accurate for estimating SI and may be used to monitor injurious ventilation in patients with ARDS, in addition to plateau airway pressure.
KeywordsMechanical ventilation Waveform Ventilator-associated lung injury Overdistension Recruitment Accuracy
End-inspiratory plateau airway pressure
Visual inspection of airway pressure–time curve profiles
Peak inspiratory flow
Likelihood ratio of a positive test
Likelihood ratio of a negative test
The authors would like to express their appreciation to Khemajira Karaketklang for statistical assistance; and Sarun Kraivee for his technical assistance with ‘Datalogger’.
PW is guarantor for the entire manuscript. PW contributed to the conception, hypothesis, outline, and design of the study; data acquisition; data analysis; drafting the manuscript; and substantial involvement in its revision prior to submission. NY contributed to the design of the study; data acquisition; drafting the manuscript; and substantial involvement in its revision prior to submission.
This research received no specific grants from any funding agency in the public, commercial, or non-profit sectors.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflict of interest.
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.
Informed consent was obtained from all individual participants or the participants’next of kin.
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