Pathophysiology and Management of Acute Respiratory Distress Syndrome in Obese Patients

Michele Umbrello, MD; Jacopo Fumagalli, MD; Antonio Pesenti, MD; Davide Chiumello, MD

Disclosures

Semin Respir Crit Care Med. 2019;40(1):40-56. 

In This Article

Abstract and Introduction

Abstract

A rising prevalence of obesity is reported over time and throughout the world. At the same time, the acute respiratory distress syndrome (ARDS) remains an important public health problem, accounting for approximately 10% of intensive care unit admissions and leading to significant hospital mortality. Even in the absence of acute illnesses, obesity affects respiratory mechanics and gas exchange in the setting of a restrictive disease. In the presence of ARDS, obesity adds various challenges to a safe and effective management of respiratory support. Difficult airway management, altered lung and chest wall physiology, and positional gas trapping are routinely encountered. The management of such difficult cases is generally empiric, as it is based on small-sized, physiologic studies or on suggestions from the general anesthesia literature. The present review focuses on those cases in which ARDS is coincident with obesity, with the aim of presenting treatment options based on the current evidence. The first part summarizes the epidemiology of obesity and ARDS. Then the diagnostic challenges due to obesity-related artifacts of the different imaging techniques will be presented. A subsequent, detailed description of the altered respiratory anatomy and physiology of obesity will provide help in selecting an optimal, individually tailored strategy of support. Furthermore, we will discuss how esophageal manometry should be used to adjust the settings of positive end-expiratory pressure and tidal volume; the challenges of prone positioning and extracorporeal support; and the optimal strategies for weaning from mechanical ventilation, including when and how to perform a tracheostomy.

Introduction

The obesity pandemic continues, with a rising prevalence reported throughout the world.[1] Even in the absence of acute illness, obesity induces major changes on cardiopulmonary physiology. In fact, it directly affects respiratory mechanics, since it increases oxygen consumption and carbon dioxide production, while at the same time increases the work of breathing in the setting of a restrictive respiratory disease.

Up to one in five critically ill patients admitted to intensive care units (ICUs) worldwide has been shown to suffer from obesity.[2] Moreover, the number of obese patients admitted to the ICU with acute respiratory failure is likely to increase in the near future. The present review focuses on those cases in which acute respiratory distress syndrome (ARDS) is coincident with obesity. High-level evidence coming from well-designed, large, multicenter randomized controlled trials on respiratory management is lacking for this population. In fact, the management of such cases is rather empiric, and it is generally based on small-sized, single-center studies or on treatment suggestions from the general anesthesia literature.

Besides the differences in respiratory physiology in obese compared with nonobese individuals, additional considerations for disease mechanism, management, and prognosis should be taken into account, as well as specific ventilator settings should be used to minimize potentially adverse consequences. As far as specific forms of support such as prone positioning, the use of extracorporeal assistance, or the technique for performing a tracheostomy are considered, we will see how the old dogmas of a strict contraindication for obesity have been challenged.

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