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

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

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.

Conflict of interest statement

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

Copyright © 2022 British Journal of Anaesthesia. Published by Elsevier Ltd. All rights reserved.

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.

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.
    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.
    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.
    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.
    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.
    1. Morales-Quinteros L., Schultz M.J., Bringué J., et al. MARS Consortium Estimated dead space fraction and the ventilatory ratio are associated with mortality in early ARDS. Ann Intensive Care. 2019;9:128.
    1. Sinha P., Calfee C.S., Beitler J.R., et al. Physiologic analysis and clinical performance of the ventilatory ratio in acute respiratory distress syndrome. Am J Respir Crit Care Med. 2019;199:333–341.
    1. Sinha P., Fauvel N.J., Singh P., Soni N. Analysis of ventilatory ratio as a novel method to monitor ventilatory adequacy at the bedside. Crit Care. 2013;17:R34.
    1. Ranieri V.M., Rubenfeld G.D., Thompson B.T., et al. ARDS Definition Task Force Acute respiratory distress syndrome: the Berlin Definition. JAMA. 2012;307:2526–2533.
    1. Harris A., Benedict F. A biometric study of human basal metabolism. Proc Natl Acad Sci U S A. 1918;4:370–373.
    1. Kuwabara S., Duncalf D. Effect of anatomic shunt on physiologic deadspace-to-tidal volume ratio—a new equation. Anesthesiology. 1969;31:575–577.
    1. Douglas A.R., Jones N.L., Reed J.W. Calculation of whole blood CO2 content. J Appl Physiol. 1988;65:473–477.
    1. Herrmann P., Nguyen X., Luecke T., Quintel M. MALUNA 1.03 a software tool for the analysis of computed tomographic slice images of the lung. Jamal R Jaschinski H Published Online. 2002:389–395.
    1. Herrmann P., Busana M., Cressoni M., et al. Using artificial intelligence for automatic segmentation of CT lung images in acute respiratory distress syndrome. Front Physiol. 2021;12
    1. Nunn J.F. Ventilation nomograms during anaesthesia. Anaesthesia. 1960;15:65.
    1. Rossi S., Palumbo M.M., Sverzellati N., et al. Mechanisms of oxygenation responses to proning and recruitment in COVID-19 pneumonia. Intensive Care Med. 2022;48:56–66.
    1. Bohr C. Ueber die Lungenathmung1. Skand Arch Für Physiol. 1891;2:236–268.
    1. Riley R.L., Lilienthal J.L., Proemmel D.D., Franke R.E. On the determination of the physiologically effective pressures of oxygen and carbon dioxide in alveolar air. Am J Physiol. 1946;147:191–198.
    1. Enghoff H. Volumen inefficax. Bermekungen zur Frage des shadlichen Raumes. Upsala Lakareforen Forh. 1938;44:191–218.

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