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INTRODUCTION

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The respiratory system primarily functions to provide adequate oxygenation and carbon dioxide elimination for the purposes of sustaining aerobic metabolism and pH homeostasis. Acute respiratory failure (ARF) is broadly defined as the inability to effectively manage gas exchange due to an impairment of the respiratory system. Although the etiologies of respiratory failure are too numerous to list, the underlying pathophysiologic mechanisms are similar and usually lead to a final common pathway. A consensus definition has not been established for ARF. Several large studies have defined severe ARF or acute respiratory distress syndrome (ARDS) as a PaO2/FiO2 ratio <200, or PaO2 <60 with either a FiO2 of >0.6 (hypoxemic) or a PaCO2 >50 (hypercapnic). ARDS recently has been redefined. The American European Consensus definition had been used since 1994 and was replaced with the Berlin definition in 20121,2 (Table 10-1). Irrespective of the criterion used to establish ARF, it can generally be stated that all patients with respiratory impairment will have either primary ventilatory or primary oxygenation impairment (Figure 10-1).

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TABLE 10-1:

Definition of ARDS: North American European Consensus Conference and Berlin Definition

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FIGURE 10-1

Common causes of acute respiratory failure in the ICU.

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ARF is one of the leading causes of admission to the intensive care unit (ICU). Incidence ranges for ARF, acute lung injury (ALI), and ARDS in adults were found to be 77.6–88.6, 17.9–34.0, and 12.6–28.0 cases/100,000 population per year, respectively.3,4 Mortality rates of approximately 40% were reported for patients with ARF, and similar or slightly lower rates for those with ALI and ARDS.5,6 A population based, pre-hospital study evaluated 19,858 cases for respiratory distress and found one-third of those required intensive care admission. The most common discharge diagnoses for patients admitted to the hospital were congestive heart failure (CHF; 16%), pneumonia (15%), chronic obstructive pulmonary disease (COPD; 13%), and acute respiratory failure (13%).7

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Physiologically, the respiratory system is composed of the lung and the respiratory pump. The respiratory pump consists of the chest wall, respiratory muscles, and the central nervous system innervations. Four types of respiratory failure are typically defined; they ...

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