Pulmonology ·
Active expiration alters regional responses to PEEP in hypoxemic patients
A secondary analysis of two randomized crossover physiological studies examined responses to low and high PEEP in 31 hypoxemic patients receiving invasive or noninvasive support. Active expiration was more common at high PEEP and was associated with a smaller increase in end-expiratory lung volume, alongside dorsal redistribution of tidal ventilation and increased regional strain.
- Active expiration was more frequent at high PEEP.
- Global EELI increased less with active expiration.
- PEEP redistributed ventilation dorsally and increased dorsal strain.
- Exploratory findings do not establish a change in PEEP practice.
This secondary analysis included 31 hypoxemic patients receiving invasive ventilation (18) or noninvasive support (13). In randomized order, patients received low PEEP (2–5 cm H₂O) and high PEEP (14–15 cm H₂O) at constant inspiratory assistance. Researchers assessed expiratory activity using gastric manometry and measured respiratory pressures and regional ventilation, including end-expiratory lung impedance (EELI), with manometry and electrical impedance tomography. Analyses were exploratory and not adjusted for multiple comparisons.
Active expiration was detected in 10 patients (32%) at low PEEP and 22 (71%) at high PEEP. The increase in global EELI with PEEP was smaller in patients with active expiration than in those with passive expiration (median increase 941 vs 2,348 arbitrary units; p=0.03). In the active-expiration group, PEEP increased ventral but not dorsal EELI and redistributed tidal ventilation dorsally. This group also had a greater tidal recruitment/derecruitment fraction (13% vs 6%; p=0.004) and increased dorsal dynamic strain.
Oxygenation improved with PEEP in patients with active expiration, despite the smaller overall lung-volume increase and regional mechanical changes. The authors caution that oxygenation may not reflect these regional effects. The small sample, secondary design and unadjusted exploratory comparisons limit interpretation; the findings do not establish that PEEP should be changed in clinical practice.
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Critical Care: Expiratory muscle activity and the physiological response to PEEP in hypoxemic patients ↗This is an automated AI-condensed summary that has not yet been reviewed by an editor. Always consult the full item at the original source.