ABSTRACT
Air trapping and auto-PEEP as a result of severe airflow limitation are the primary pathophysiologic abnormalities leading to mechanical ventilation of patients presenting in an exacerbation of COPD or severe acute asthma. AutoPEEP is a primary cause of patient ventilator dyssynchrony but also exerts similar cardiopulmonary effects as applied PEEP1. Functional residual capacity is increased, intrathoracic pressure is increased, hemodynamics are compromised and ventilationperfusion mismatch is increased1. In addition, work of breathing is markedly increased and the efficiency of diaphragmatic contraction decreased2. Air trapping and auto-PEEP flatten the diaphragm, frequently eliminating its inspiratory muscle capabilities and changing its motion to expiratory in function2. The altered pulmonary mechanics observed as auto-PEEP increases frequently leads to the ventilatory muscle dysfunction and blood gas abnormalities that require initiation of mechanical ventilation in COPD and asthma.
