Extrinsic positive end-expiratory pressure (PEEP) reduces the work of breathing in status asthmaticus

The figure compares three conditions: No intrinsic or extrinsic positive end-expiratory pressure (PEEP), intrinsic PEEP only, and intrinsic plus extrinsic PEEP. When intrinsic PEEP exists, the addition of extrinsic PEEP reduces inspiratory effort (shown in red) from -11 cm H₂O to -3 cm H₂O. Airflow obstruction is inhomogenous, so levels of intrinsic PEEP are likely to vary from airway to airway. Thus, as a general rule, extrinsic PEEP is usually set up to, but not exceeding, 80 percent of the measured intrinsic PEEP in order to prevent regions of worsening dynamic hyperinflation.