Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
Observational Study
. 2023 Mar;130(3):360-367.
doi: 10.1016/j.bja.2022.10.035. Epub 2022 Dec 2.

Ventilatory ratio, dead space, and venous admixture in patients with acute respiratory distress syndrome

Roberta Maj  1 , Paola Palermo  1 , Simone Gattarello  1 , Serena Brusatori  2 , Rosanna D'Albo  2 , Carmelo Zinnato  2 , Mara Velati  1 , Federica Romitti  2 , Mattia Busana  2 , Johannes Wieditz  2 , Peter Herrmann  2 , Onnen Moerer  2 , Micheal Quintel  2 , Konrad Meissner  2 , Barnaby Sanderson  3 , Davide Chiumello  4 , John J Marini  5 , Luigi Camporota  3 , Luciano Gattinoni  6
Affiliations
Observational Study

Ventilatory ratio, dead space, and venous admixture in patients with acute respiratory distress syndrome

Roberta Maj et al. Br J Anaesth. 2023 Mar.

Abstract

Background: Ventilatory ratio (VR) has been proposed as an alternative approach to estimate physiological dead space. However, the absolute value of VR, at constant dead space, might be affected by venous admixture and CO2 volume expired per minute (VCO2).

Methods: This was a retrospective, observational study of mechanically ventilated patients with acute respiratory distress syndrome (ARDS) in the UK and Italy. Venous admixture was either directly measured or estimated using the surrogate measure PaO2/FiO2 ratio. VCO2 was estimated through the resting energy expenditure derived from the Harris-Benedict formula.

Results: A total of 641 mechanically ventilated patients with mild (n=65), moderate (n=363), or severe (n=213) ARDS were studied. Venous admixture was measured (n=153 patients) or estimated using the PaO2/FiO2 ratio (n=448). The VR increased exponentially as a function of the dead space, and the absolute values of this relationship were a function of VCO2. At a physiological dead space of 0.6, VR was 1.1, 1.4, and 1.7 in patients with VCO2 equal to 200, 250, and 300, respectively. VR was independently associated with mortality (odds ratio [OR]=2.5; 95% confidence interval [CI], 1.8-3.5), but was not associated when adjusted for VD/VTphys, VCO2, PaO2/FiO2 (ORadj=1.2; 95% CI, 0.7-2.1). These three variables remained independent predictors of ICU mortality (VD/VTphys [ORadj=17.9; 95% CI, 1.8-185; P<0.05]; VCO2 [ORadj=0.99; 95% CI, 0.99-1.00; P<0.001]; and PaO2/FiO2 (ORadj=0.99; 95% CI, 0.99-1.00; P<0.001]).

Conclusions: 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.

Keywords: ARDS; dead space; mechanical ventilation; venous admixture; ventilatory ratio.

PubMed Disclaimer

Conflict of interest statement

LG reports a consultancy for General Electric and SIDAM. He also receives lecture fees from Estor and Mindray.

Figures

Fig 1
Fig 1
(a) Theoretical model: ventilatory ratio as a function of the physiological dead space at VCO2 equal to 186 ml min−1 (median of the clinical cohort – blue line), 228 ml min−1 (50% above the median – red line), and 142 ml min−1 (50% below the median). (b) Clinical cohort (n=641): ventilatory ratio as a function of physiological dead space. Patients with VCO2 higher than median (186 ml min−1) are represented by red points (average VCO2 equal to 208 (29) ml min−1); patients with VCO2 below the median are represented by green points (average VCO2 equal to 164 (17) ml min−1).
Fig 2
Fig 2
(a) Theoretical model: the true physiological dead space as a function of physiological dead space at different venous admixture. The blue line is the identity line (venous admixture equal to zero), green line denotes venous admixture equals to 0.31, whereas the red line has venous admixture equal to 0.48. (b) Corrected dead space as a function of the physiological dead space in the clinical cohort of patients in which venous admixture was available. The venous admixture levels were the average above the median (0.31 [0.07]) and below the median (0.48 [0.13]).
Fig 3
Fig 3
Effect of the venous admixture, measured as difference between ventilatory ratio and ventilatory ratio corrected for venous admixture, in different classes of ARDS severity. The greater is the venous admixture, the higher is its effect on the difference between measured and corrected ventilatory ratios. ARDS, acute respiratory distress syndrome; VR, ventilatory ratio.
See this image and copyright information in PMC

References

    1. Gattinoni L., Bombino M., Pelosi P., et al. Lung structure and function in different stages of severe adult respiratory distress syndrome. JAMA. 1994;271:1772–1779. - PubMed
    1. Nuckton T.J., Pittet J.F. Pulmonary dead-space fraction as a risk factor for death in the acute respiratory distress syndrome. N Engl J Med. 2002;346:1281–1286. - PubMed
    1. Cressoni M., Cadringher P., Chiurazzi C., et al. Lung inhomogeneity in patients with acute respiratory distress syndrome. Am J Respir Crit Care Med. 2014;189:149–158. - PubMed
    1. Kallet R.H., Zhuo H., Liu K.D., Calfee C.S., Matthay M.A. On behalf of the National Heart Lung and Blood Institute ARDS Network Investigators. The association between physiologic dead-space fraction and mortality in subjects with ARDS enrolled in a prospective multi-center clinical trial. Respir Care. 2014;59:1611–1618. - PMC - PubMed
    1. Sinha P., Fauvel N.J., Singh S., Soni N. Ventilatory ratio: a simple bedside measure of ventilation. Br J Anaesth. 2009;102:692–697. - PubMed

Publication types