DYNAMIC HYPERINFLATION AND INTRINSIC PEEP DURING MECHANICAL VENTILATION

Dynamic hyperinflation, also called intrinsic PEEP (PEEPi,) occurs par ticularly when high tidal volumes or high respiratory rates are used d uring mechanical ventilation, although the phenomenon does occur at no rmal tidal volumes. It is not identified using existing monitoring suc h as the airway pressure but can be identified by occlusion of the exp iratory port before the onset of the next positive pressure breath. Ma ny factors contribute to PEEPi which has unfavourable effects on respi ratory muscle activity. Inhomogenicity of the time constants is a majo r aetiological factor. Fine tuning of positive pressure ventilation, u sing low tidal volumes, short inspiratory times and adequate inspired oxygen are required. External PEEP, up to but not exceeding PEEPi, may be advisable. PEEP may be used therapeutically to improve gas exchang e by inverse ratio ventilation or high frequency jet ventilation.