Automatic tailoring of the lowest PEEP to abolish tidal expiratory flow limitation in seated and supine COPD patients

Rationale: In COPD patients, the development of tidal expiratory flow limitation (EFLT) results in intrinsic positive end-expiratory pressure (PEEPi), leading to increased work of breathing and worsening patient-ventilator interaction. An external PEEP can mitigate these consequences, but how to optimize its value it is still unknown. Objective: To measure the minimum PEEP able to abolish EFLT by a new automatic non-invasive ventilation (NIV) mode in stable hypercapnic COPD patients in the seated and supine positions. Methods: Twenty-six hypercapnic COPD patients (mean±SD: FEV1%pred = 39.2 ± 16.1, FEV1/FVC%pred = 46.3 ± 16.3%) were studied while receiving NIV during two consecutive 15-min periods, with patients studied seated in the first and supine in the second. A ventilator able to identify EFLT breath-by-breath by using the forced oscillation technique optimized in real-time PEEP to the lowest pressure able to abolish EFLT (PEEPO). Results: The ventilator was always able to identify a PEEPO. Its values were highly variable among patients and increased from median(iqr) 4.0 (0.03) (range: 4.0–8.3cmH2O) to 6 (6.1) cmH2O (range: 4.0–15.7 cmH2O) when patients moved from the seated to the supine position, respectively. PEEPO in supine position did not correlate to any spirometric or anthropometric variable. Conclusions: PEEPO in COPD patients is highly variable and increases in supine position. It is not predicted by spirometric nor anthropometric variables, but had a considerable variability among the patients. We suggest that PEEPo may be used as a phenotyping variable in COPD patients.