Ventilatory strategies in obstructive lung disease

Abstract

Chronic obstructive pulmonary disease (COPD) is characterized by expiratory flow limitation (EFL) due to progressive airflow obstruction. The various mechanisms that cause EFL are central to understanding the physiopathology of COPD. At the end of expiration, dynamic inflation may occur due to incomplete emptying the lungs. This "extra" volume increases the alveolar pressure at the end of the expiration, resulting in auto-positive end-expiratory pressure (PEEP) or PEEPi. Acute exacerbations of COPD may result in increased airway resistance and inspiratory effort, further leading to dynamic hyperinflation. COPD exacerbations may be triggered by environmental exposures, infections (viral and bacterial), or bronchial inflammation, and may result in worsening respiratory failure requiring mechanical ventilation (MV). Acute exacerbations of COPD need to be distinguished from other events such as cardiac failure or pulmonary emboli. Strategies to treat acute respiratory failure (ARF) in COPD patients include noninvasive ventilation (NIV), pressure support ventilation, and tracheal intubation with MV. In this review, we discuss invasive and noninvasive techniques to address ARF in this patient population. When invasive MV is used, settings should be adjusted in a way that minimizes hyperinflation, while providing reasonable gas exchange, respiratory muscle rest, and proper patient-ventilator interaction. Further, weaning from MV may be difficult in these patients, and factors amenable to pharmacological correction (such as increased bronchial resistance, tracheobronchial infections, and heart failure) are to be systematically searched and treated. In selected patients, early use of NIV may hasten the process of weaning from MV and improve outcomes.