INSPIRATORY EFFORT AND MEASUREMENT OF DYNAMIC INTRINSIC PEEP IN COPD PATIENTS - EFFECTS OF VENTILATOR TRIGGERING SYSTEMS

Objective: To investigate effects of ventilator triggering systems (pr essure and flow triggering: PT and FT) on measurement of dynamic intri nsic PEEP (PEEPi(dyn)) and patient-ventilator interaction in patients with chronic obstructive pulmonary disease during weaning from mechani cal ventilation. Design: Prospective study. Setting: Medical/surgical intensive care unit of an academic hospital. Patients and participants : 6 COPD patients with acute respiratory failure ready to wean. Measur ements: We measured flow, airway opening, esophageal and gastric press ures. Minute ventilation, breathing pattern and pressure time product (PTP) of the respiratory muscles and of the diaphragm were obtained du ring spontaneous ventilation through a mechanical ventilator (Puritan- Bennett 7200 ae). Two triggering systems, namely PT and FT, were evalu ated. Results: The inspiratory muscles effort necessary to overcome th e triggering system overestimated PEEPi(dyn) measurement of an amount equal to 49+/-2 and 58+/-3% during respectively pressure and flow trig gering. FT increased tidal volume and minute ventilation and decrease PTP/b and PTP/min of the respiratory muscles and diaphragm. Conclusion s: To correctly measure PEEPi(dyn), the inspiratory effort produced to overcome PEEPi and to trigger the ventilator must be discriminated. A pplication of flow triggering requires less effort to initiate inspira tion and provide a positive end-expiratory pressure level that is able to unload the respiratory muscles by reducing PEEPi. With flow trigge ring higher minute ventilation are obtained in COPD patients during th e weaning phase.