Expiratory flow limitation during mechanical ventilation: real-time detection and physiological subtypes

Tidal expiratory flow limitation (EFL_T) complicates the delivery of mechanical ventilation but is only diagnosed by performing specific manoeuvres. Instantaneous analysis of expiratory resistance (Rex) can be an alternative way to detect EFL_T without changing ventilatory settings. This study aimed to determine the agreement of EFL_T detection by Rex analysis and the PEEP reduction manoeuvre using contingency table and agreement coefficient. The patterns of Rex were explored.

Medical patients ≥ 15-year-old receiving mechanical ventilation underwent a PEEP reduction manoeuvre from 5 cmH₂O to zero for EFL_T detection. Waveforms were recorded and analyzed off-line. The instantaneous Rex was calculated and was plotted against the volume axis, overlapped by the flow-volume loop for inspection. Lung mechanics, characteristics of the patients, and clinical outcomes were collected. The result of the Rex method was validated using a separate independent dataset.

339 patients initially enrolled and underwent a PEEP reduction. The prevalence of EFL_T was 16.5%. EFL_T patients had higher adjusted hospital mortality than non-EFL_T cases. The Rex method showed 20% prevalence of EFL_T and the result was 90.3% in agreement with PEEP reduction manoeuvre. In the validation dataset, the Rex method had resulted in 91.4% agreement. Three patterns of Rex were identified: no EFL_T, early EFL_T, associated with airway disease, and late EFL_T, associated with non-airway diseases, including obesity. In early EFL_T, external PEEP was less likely to eliminate EFL_T.

The Rex method shows an excellent agreement with the PEEP reduction manoeuvre and allows real-time detection of EFL_T. Two subtypes of EFL_T are identified by Rex analysis.

Clinical trial registered with www.thaiclinicaltrials.org (TCTR20190318003). The registration date was on 18 March 2019, and the first subject enrollment was performed on 26 March 2019.