Ventilatory ratio, dead space, and venous admixture in patients with acute respiratory distress syndrome. 2023

Roberta Maj, and Paola Palermo, and Simone Gattarello, and Serena Brusatori, and Rosanna D'Albo, and Carmelo Zinnato, and Mara Velati, and Federica Romitti, and Mattia Busana, and Johannes Wieditz, and Peter Herrmann, and Onnen Moerer, and Micheal Quintel, and Konrad Meissner, and Barnaby Sanderson, and Davide Chiumello, and John J Marini, and Luigi Camporota, and Luciano Gattinoni
Department of Anaesthesiology, Medical University of Göttingen, University Medical Centre Göttingen, Göttingen, Germany; Department of Anaesthesia and Intensive Care, IRCCS San Raffaele Scientific Institute, Milan, Italy.

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). 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. 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]). 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.

UI MeSH Term Description Entries
D007558 Italy A country in southern Europe, a peninsula extending into the central Mediterranean Sea, northeast of Tunisia. The capital is Rome. Sardinia
D012119 Respiration The act of breathing with the LUNGS, consisting of INHALATION, or the taking into the lungs of the ambient air, and of EXHALATION, or the expelling of the modified air which contains more CARBON DIOXIDE than the air taken in (Blakiston's Gould Medical Dictionary, 4th ed.). This does not include tissue respiration ( Breathing
D012121 Respiration, Artificial Any method of artificial breathing that employs mechanical or non-mechanical means to force the air into and out of the lungs. Artificial respiration or ventilation is used in individuals who have stopped breathing or have RESPIRATORY INSUFFICIENCY to increase their intake of oxygen (O2) and excretion of carbon dioxide (CO2). Ventilation, Mechanical,Mechanical Ventilation,Artificial Respiration,Artificial Respirations,Mechanical Ventilations,Respirations, Artificial,Ventilations, Mechanical
D012126 Respiratory Dead Space That part of the RESPIRATORY TRACT or the air within the respiratory tract that does not exchange OXYGEN and CARBON DIOXIDE with pulmonary capillary blood. Dead Space, Respiratory,Dead Spaces, Respiratory,Respiratory Dead Spaces,Space, Respiratory Dead,Spaces, Respiratory Dead
D012128 Respiratory Distress Syndrome A syndrome characterized by progressive life-threatening RESPIRATORY INSUFFICIENCY in the absence of known LUNG DISEASES, usually following a systemic insult such as surgery or major TRAUMA. ARDS, Human,Acute Respiratory Distress Syndrome,Adult Respiratory Distress Syndrome,Pediatric Respiratory Distress Syndrome,Respiratory Distress Syndrome, Acute,Respiratory Distress Syndrome, Adult,Respiratory Distress Syndrome, Pediatric,Shock Lung,Distress Syndrome, Respiratory,Distress Syndromes, Respiratory,Human ARDS,Lung, Shock,Respiratory Distress Syndromes,Syndrome, Respiratory Distress
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D012189 Retrospective Studies Studies used to test etiologic hypotheses in which inferences about an exposure to putative causal factors are derived from data relating to characteristics of persons under study or to events or experiences in their past. The essential feature is that some of the persons under study have the disease or outcome of interest and their characteristics are compared with those of unaffected persons. Retrospective Study,Studies, Retrospective,Study, Retrospective

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