Prevalence of Complete Airway Closure According to Body Mass Index in Acute Respiratory Distress Syndrome

Abstract

Background Complete airway closure during expiration may underestimate alveolar pressure. It has been reported in cases of acute respiratory distress syndrome (ARDS), as well as in morbidly obese patients with healthy lungs. The authors hypothesized that complete airway closure was highly prevalent in obese ARDS and influenced the calculation of respiratory mechanics. Methods In a post hoc pooled analysis of two cohorts, ARDS patients were classified according to body mass index (BMI) terciles. Low-flow inflation pressure–volume curve and partitioned respiratory mechanics using esophageal manometry were recorded. The authors’ primary aim was to compare the prevalence of complete airway closure according to BMI terciles. Secondary aims were to compare (1) respiratory system mechanics considering or not considering complete airway closure in their calculation, and (2) and partitioned respiratory mechanics according to BMI. Results Among the 51 patients analyzed, BMI was less than 30 kg/m2 in 18, from 30 to less than 40 in 16, and greater than or equal to 40 in 17. Prevalence of complete airway closure was 41% overall (95% CI, 28 to 55; 21 of 51 patients), and was lower in the lowest (22% [3 to 41]; 4 of 18 patients) than in the highest BMI tercile (65% [42 to 87]; 11 of 17 patients). Driving pressure and elastances of the respiratory system and of the lung were higher when complete airway closure was not taken into account in their calculation. End-expiratory esophageal pressure (ρ = 0.69 [95% CI, 0.48 to 0.82]; P < 0.001), but not chest wall elastance, was associated with BMI, whereas elastance of the lung was negatively correlated with BMI (ρ = −0.27 [95% CI, −0.56 to −0.10]; P = 0.014). Conclusions Prevalence of complete airway closure was high in ARDS and should be taken into account when calculating respiratory mechanics, especially in the most morbidly obese patients. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

When could airway plateau pressure above 30 cmH2O be acceptable in ARDS patients?

“…This situation can be present in obese patients, patients with fluid overload or abdominal distension. These patients have normal or near-normal E CW values [9]. Panels c and d of Fig.…”

“…While waiting further studies on this topic, such a selection could be based on the medical history of the patients and on baseline characteristics, such as BMI values. Of note, even if a rather good correlation (R 2 = 0.45) was found between end-expiratory P es and BMI in a series of 51 ARDS patients [9], it is likely that other factors, such as the distribution of obesity (central, abdominal, etc.) and the abdominal elastance, are important to consider.…”

Impact of Obesity in Critical Illness

“…32 Finally, accurate assessment of lung compliance and driving pressure, used to optimize PEEP settings, may be complicated by endexpiratory complete airway closure, present in up to two-thirds of patients with ARDS with BMI $ 40 kg/ m 2 . 33 At PEEP below airway opening pressure, standard end-expiratory airway pressure measurements may therefore underestimate alveolar pressure and chestjournal.org overestimate driving pressure and respiratory system elastance. There is a sound physiological basis, however, for a higher PEEP approach in patients with very high BMI, and trials testing clinical outcomes using this strategy in the obese population are clearly warranted.…”

A rational approach on the use of extracorporeal membrane oxygenation in severe hypoxemia: advanced technology is not a panacea

“…Individual titration of mechanical ventilation based, among others, on esophageal manometry might be particularly valuable in obese patients and could improve their outcome compared to standard practice [ 103 ]. In this group, the high prevalence of complete airway closure (> 41%), can make driving pressures unreliable [ 104 ]. Furthermore, the hemodynamic tolerance to high PEEP was found remarkably good in class III obese patients (mean BMI = 57 kg/m 2 ) [ 105 ].…”