Influence of body mass index on respiratory mechanics in acute respiratory distress syndrome: a multicenter cohort study.
CCCF ePoster library. Coudroy R. 11/13/19; 283416; EP133
Remi Coudroy
Remi Coudroy
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Topic: Retrospective or Prospective Cohort Study or Case Series

Coudroy, Remi1,2,3,4;Vimpere, Damien5; Aissaoui, Nadia5; Younan, Romy5; Bailleul, Clotilde5; Couteau-Chardon, Amélie5; Lancelot, Aymeric5; Guerot, Emmanuel5; Chen, Lu1,2; Diehl, Jean-Luc5; Brochard, Laurent1,2

1 Interdepartmental Division of Critical Care Medicine, University of Toronto, Toronto, Canada.
2 Department of Critical Care, St Michael's Hospital, Keenan Research Centre and Li Ka Shing Knowledge Institute, Toronto, Canada
3 Médecine Intensive et Réanimation, CHU de Poitiers, Poitiers, France
4 INSERM CIC 1402, ALIVE research group, Université de Poitiers, Poitiers, France
5 Department of Medical Intensive Care, Hôpital Européen Georges Pompidou, Assistance Publique-Hôpitaux de Paris, Paris, France.

Overweight and obesity are increasingly prevalent worldwide and account for about 30-40% of patients with acute respiratory distress syndrome (ARDS). How body mass index (BMI) influences respiratory mechanics in ARDS is unclear.
Our objective is to compare the respiratory mechanics of obese and non-obese ARDS and to assess the influence of BMI on respiratory mechanics.
This study is a secondary analysis of 2 cohorts of ARDS according to the Berlin definition: a bicenter Canadian study of 44 ARDS of any BMI enrolled in a prospective study (NCT02457741), and a French monocenter cohort of 9 selected ARDS with a BMI > 40 kg/m2. Airway pressure, flow and esophageal pressure were collected in all patients and we report data at a set positive end-expiratory pressure (PEEP) of 5 cmH2O. Presence of complete airway closure and airway opening pressure were assessed using a low-flow inflation pressure-volume curve.
Patients were sorted in 3 groups according to the World Health Organization overweight classification (BMI<30, from 30 to 40, and ≥40 kg/m2).
Among the 53 patients included, 18 patients (34%) had BMI<30 kg/m2, 16 (30%) from 30 to 40 kg/m2, and 19 (36%) ≥40 kg/m2. Overall, PaO2/FiO2 was 137 mmHg with a PEEP of 15 cmH2O, and mortality was 32% without difference across groups.
Airway closure occurrence increased with BMI (22%, 38% and 58%, p=0.04). When present, the airway opening pressure was 9.6 cmH2O (8.5-13.2) and similar between the 3 groups. With increasing BMI, total PEEP at a PEEP of 5 cmH2O increased from 6.0 to 9.0 cmH2O (p=0.02) across groups due differences in respiratory rate, respiratory system resistance and time constant of the respiratory system between the 3 groups. All values of esophageal pressure increased with BMI with a strong correlation between end-expiratory esophageal pressure and BMI (Rho=0.71, p<0.001, see Figure 1). Consequently end-expiratory transpulmonary pressure et a PEEP of 5 cmH2O decreased from -2.7 to -9.3 cm H2O with increasing BMI (Rho=0.56, p<0.001).
Respiratory system and lung elastances were significantly and negatively related to BMI, whereas chest wall elastance was not influenced by BMI. As a consequence, the chest wall to respiratory system elastance ratio increased significantly with respect to BMI, suggesting the amount of airway pressure at end-inspiration bore by the chest wall increases with BMI.
In ARDS, increasing BMI was associated with increased occurrence of airway closure, increased values of esophageal pressure and decreased values of end-expiratory transpulmonary pressure. Although chest wall elastance was not influenced by BMI, respiratory system and lung elastances decreased with BMI, and the chest wall to respiratory system elastance ratio increased. All in all, these results suggest that increasing PEEP in obese patients could be necessary to decrease atelectrauma in the dependent lung, and safe in limiting overdistension in the non-dependent lung. Including BMI in the interpretation of ARDS respiratory mechanics can provide important additional information for the clinical management of obese patients.

Figure 1. Relationship between individual values of end-expiratory esophageal pressure and body mass index (Spearman's Rho= 0.72). The dotted line represents the regression line (R2 = 0.48, p < 0.001). BMI: Body Mass Index; end-expiratory esophageal pressure.


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