Respiratory failure & ventilation
Effects of increasing respiratory rate on ventilatory efficiency and mechanical costs during low-tidal-volume ventilation: a prospective physiological pilot study
Authors' conclusion
In this physiological study, RR escalation during low-tidal volume ventilation was associated with progressive decline in ventilatory efficiency, driven by increasing dead space fraction and compounded by rising CO2 rebreathing.
Study context
- Population
- Mechanically ventilated ICU patients under low-tidal-volume controlled ventilationprimary analysis RR ≤27 min-1
- Participants
- 30 participants
- Exposure
- Complete expiration vs Fixed I:E
- Outcome
- Physiological effects of RR escalation (dead space, ventilatory efficiency, mechanical power)
Methodological detailsstepwise RR escalation at fixed tidal volume, two protocols: complete expiration and fixed I:E ratio (1:1.9)
- Stepwise RR escalation at fixed tidal volume
- Two protocols: complete expiration and fixed I:E ratio (1:1.9)
Main finding
As reported in the abstract
- PaCO2 reduction with 50% increase in minute ventilation (RR 17→25 min-1), less than predicted assuming constant dead space fraction
- 5.1 mmHg (95% CI 4.2-5.9)
- Alveolar dead space increase (mL)
- 132 to 189 (p < 0.001)
- Dead space fraction increase
- 0.60 to 0.65
- Decline in incremental CO2 elimination efficiency with increasing RR (β, ml CO2/L MV per min-1), suggesting plateau under complete expiration
- −0.95 (95% CI −1.41 to −0.49)
- Mechanical power increase at 27 min-1, complete expiration (exponential)
- +181%
- Mechanical power increase at 27 min-1, fixed I:E
- +122%
Observational data: associations, not effects.
Further findings
V̇CO2 trajectories by baseline ventilatory ratio (VR) (subgroup)
- High-VR patients tended to show declining CO2 elimination beyond 21-24 min-1; low-VR patients showed approximately linear increases
Original publication
Effects of increasing respiratory rate on ventilatory efficiency and mechanical costs during low-tidal-volume ventilation: a prospective physiological pilot study. Ann Intensive Care. Published 2 June 2026. doi:10.
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