Respiratory failure & ventilation
Ventilatory ratio, dead space, and venous admixture in patients with acute respiratory distress syndrome
Authors' conclusion
VR is a useful aggregate variable associated with outcome, but variables not associated with ventilation (VCO2 and venous admixture) strongly contribute to the high values of VR seen in patients with severe illness.
Study context
- Population
- Mechanically ventilated patients with acute respiratory distress syndrome (ARDS) in the UK and Italy
- Participants
- 641 participants
- Exposure
- Mild ARDS vs Moderate ARDS vs Severe ARDS
- Mild ARDSn = 65
- Moderate ARDSn = 363
- Severe ARDSn = 213
- Outcome
- Relationship of VR with physiological dead space and VCO2
Methodological detailsmultinational (UK and Italy), Venous admixture measured (n=153) or estimated by PaO2/FiO2 (n=448); VCO2 estimated from Harris-Benedict resting energy expenditure
- Multinational (UK and Italy)
- Venous admixture measured (n=153) or estimated by PaO2/FiO2 (n=448); VCO2 estimated from Harris-Benedict resting energy expenditure
Main finding
As reported in the abstract
Ventilatory ratio (VR) at physiological dead space 0.6, VCO2 200
1.1
VR at physiological dead space 0.6, VCO2 250
1.4
VR at physiological dead space 0.6, VCO2 300
1.7
Observational data: associations, not effects.
Further findings
Mortality associated with VR
| Estimate | ||
|---|---|---|
| VR | OR 2.5 (95% CI 1.8–3.5) | |
| VRAdjusted for VD/VTphys, VCO2, PaO2/FiO2 | ORadj 1.2 (95% CI 0.7–2.1) | |
| 0.20.5125Ratio (log scale) |
Independent predictors of ICU mortality
| ORadj (95% CI) | P value | ||
|---|---|---|---|
| VD/VTphys | 17.9 (1.8–185) | P < 0.05 | |
| VCO2 | 0.99 (0.99–1.00) | P < 0.001 | |
| PaO2/FiO2 | 0.99 (0.99–1.00) | P < 0.001 | |
| 0.050.21520Adjusted odds ratio (log scale) |
Original publication
Ventilatory ratio, dead space, and venous admixture in patients with acute respiratory distress syndrome. Br J Anaesth. Published 2 December 2022. doi:10.
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