Figure 6

Measurement of intrinsic positive end-expiratory pressure. Intrinsic positive end-expiratory pressure is the lowest average alveolar pressure achieved during the respiratory cycle and is obtained by an end-expiratory hold manoeuvre. In the non-obstructed patient, alveolar pressure (P_ALV) equals pressure at the airway opening (P_AO) both at end inspiration and end expiration. In the severely obstructed patient, P_ALV may increase because of air trapping, and at end expiration P_ALV does not equal P_AO. If an expiratory hold manoeuvre is performed, P_AO will rise, reflecting the degree of lung hyperinflation. Published with permission from Principles of Critical Care [69].