Advanced respiratory mechanics assessment in mechanically ventilated obese and non-obese patients with or without acute respiratory distress syndrome

Abstract

Background Respiratory mechanics is a key element to monitor mechanically ventilated patients and guide ventilator settings. Besides the usual basic assessments, some more complex explorations may allow to better characterize patients’ respiratory mechanics and individualize ventilation strategies. These advanced respiratory mechanics assessments including esophageal pressure measurements and complete airway closure detection may be particularly relevant in critically ill obese patients. This study aimed to comprehensively assess respiratory mechanics in obese and non-obese ICU patients with or without ARDS and evaluate the contribution of advanced respiratory mechanics assessments compared to basic assessments in these patients. Methods All intubated patients admitted in two ICUs for any cause were prospectively included. Gas exchange and respiratory mechanics including esophageal pressure and end-expiratory lung volume (EELV) measurements and low-flow insufflation to detect complete airway closure were assessed in standardized conditions (tidal volume of 6 mL kg−1 predicted body weight (PBW), positive end-expiratory pressure (PEEP) of 5 cmH2O) within 24 h after intubation. Results Among the 149 analyzed patients, 52 (34.9%) were obese and 90 (60.4%) had ARDS (65.4% and 57.8% of obese and non-obese patients, respectively, p = 0.385). A complete airway closure was found in 23.5% of the patients. It was more frequent in obese than in non-obese patients (40.4% vs 14.4%, p < 0.001) and in ARDS than in non-ARDS patients (30% vs. 13.6%, p = 0.029). Respiratory system and lung compliances and EELV/PBW were similarly decreased in obese patients without ARDS and obese or non-obese patients with ARDS. Chest wall compliance was not impacted by obesity or ARDS, but end-expiratory esophageal pressure was higher in obese than in non-obese patients. Chest wall contribution to respiratory system compliance differed widely between patients but was not predictable by their general characteristics. Conclusions Most respiratory mechanics features are similar in obese non-ARDS and non-obese ARDS patients, but end-expiratory esophageal pressure is higher in obese patients. A complete airway closure can be found in around 25% of critically ill patients ventilated with a PEEP of 5 cmH2O. Advanced explorations may allow to better characterize individual respiratory mechanics and adjust ventilation strategies in some patients. Trial registration NCT03420417 ClinicalTrials.gov (February 5, 2018).

Airway opening pressure maneuver to detect airway closure in mechanically ventilated pediatric patients

“…For example, following the standard operating procedure described in Supplementary Table S2, a 10 kg patient will get 60 ml of Vt over 3 s, which gives a flowrate of 1.2 L/min. Airway closure is an increasingly recognized phenomenon in patients with obesity (10), ARDS (up to 40% of adult patients and 65% in those with body mass index of ≥40 kg/m 2 ) (7), and more recently in patients with hydrostatic pulmonary edema caused by cardiogenic shock (11). The prevalence in pediatrics is unknown; however, with the use of this adapted maneuver, it is now possible to study its prevalence in pediatric patients with ARDS or other lung diseases.…”

“…As a result, airway closure is expected to occur more often at a very young age, in patients with obesity and patients with ARDS ( 15 ). Therefore, its routine assessment has been recommended in patients with obesity and ARDS ( 10 ). Several causal factors have been postulated to contribute to airway closure in ARDS, including surfactant impairment, intraluminal fluid accumulation, bronchoconstriction, and the loss of radial traction secondary to elastic fiber destruction, with consequently decreased lung elastic recoil ( 15 ).…”

Optimal positive-end expiratory pressure weaning in acute respiratory distress syndrome patients

“…To address these altered mechanics, patients with obesity and ARDS require higher airway pressures to recruit lung units relative to patients with ARDS but normal BMI [19,20 ▪ ]. Studies comparing different PEEP titration strategies in patients with a BMI greater than 35 kg/m 2 , have shown that higher PEEP strategies result in reduced atelectasis, improved lung elastance, and better oxygenation [21].…”

Setting positive end-expiratory pressure: the use of esophageal pressure measurements

“…For a detailed practical stepby-step approach for bedside measurement of P es and its use in the full context of a lung-protective ventilation strategy, we refer to a recent publication [4 && ]. Theoretically, a P es -guided PEEP setting could prevent atelectasis formation and enhance lung recruitment, which is of particular interest in ARDS and in patients with high P Pl due to other causes, as for example patients with obesity [5]. In this review, we present key concepts and the physiological rationale for titrating PEEP using P es , we discuss the current clinical evidence for this approach, and provide considerations to facilitate bedside implementation.…”