• V M Ranieri, L Mascia, V Petruzzelli, F Bruno, A Brienza, and R Giuliani.
• Istituto di Anestesiologia e Rianimazione, Università di Bari, Ospedale Policlinico, Italy.
• Intensive Care Med. 1995 Nov 1;21(11):896-903.

ObjectiveTo investigate effects of ventilator triggering systems (pressure and flow triggering: PT and FT) on measurement of dynamic intrinsic PEEP (PEEPidyn) and patient-ventilator interaction in patients with chronic obstructive pulmonary disease during weaning from mechanical ventilation.DesignProspective study.SettingMedical/surgical intensive care unit of an academic hospital.Patients And Participants6 COPD patients with acute respiratory failure ready to wean.MeasurementsWe measured flow, airway opening, esophageal and gastric pressures. Minute ventilation, breathing pattern and pressure time product (PTP) of the respiratory muscles and of the diaphragm were obtained during spontaneous ventilation through a mechanical ventilator (Puritan-Bennett 7200ae). Two triggering systems, namely PT and FT, were evaluated.ResultsThe inspiratory muscles effort necessary to overcome the triggering system overestimated PEEPidyn measurement of an amount equal to 49 +/- 2 and 58 +/- 3% during respectively pressure and flow triggering. FT increased tidal volume and minute ventilation and decrease PTP/b and PTP/min of the respiratory muscles and diaphragm.ConclusionsTo correctly measure PEEPidyn, the inspiratory effort produced to overcome PEEPi and to trigger the ventilator must be discriminated. Application of flow triggering requires less effort to initiate inspiration and provide a positive end-expiratory pressure level that is able to unload the respiratory muscles by reducing PEEPi. With flow triggering higher minute ventilation are obtained in COPD patients during the weaning phase.

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