Variation des exspiratorischen Umschaltkriteriums während assistierter Beatmung bei chronisch obstruktiver Lungenerkrankung – Untersuchung der Patient-Ventilator-Interaktion am Lungenmodell

Abstract

Introduction: During pressure support ventilation (PSV) the ventilator cycles to the expiratory phase when the inspiratory flow falls below a predefined percentage of the peak-flow, the off-cycling criterion. In COPD delayed off-cycling is common due to the slow decrease of the inspiratory flow. The interface, the level of pressure support, the duration of patient inspiratory effort, leakage in non-invasive ventilation and the use of a niv-mode potentially influence the off-cycling. Patient-ventilator synchrony is crucial for the success of ventilation. Methods: COPD was simulated in a lung model. PSV was delivered by a standard ventilator via endotracheal tube (ET), face mask (FM) and ventilation helmet (VH). The off-cycling criterion was varied (10 %, 20 %, 30 %, 40 %, 50 %, 60 %, 70 % of peak flow) at different levels of pressure support (5 cmH2O, 15 cmH2O) and different respiratory rates (15 und 30 bpm). During non-invasive ventilation measurements were repeated with leakage using the ventilators invasive (IV) and non invasive (NIV) mode. Asynchrony-events (wasted efforts, double trigger), inspiratory (TLINSP) an expiratory trigger latency (TLEXP), intrinsic PEEP (PEEPi), pressure time products in different phases of the breathing cycle (PTPPEEP, PTPINSP, PTPEXSP) and the tidal volume (VT) were calculated to analyse the patient-ventilator interaction. Results: Using conventional off-cycling criteria (20 % to 30 % of peak flow) always resulted in delayed cycling. Augmenting the off-cycling criterion led to a reduction of TLEXP, PTPEXSP and PEEPi. Consequently wasted efforts, TLINSP and PTPPEEP were reduced. The use of high off-cycling criteria (50 % - 70 %) caused premature cycling in some situations which was associated with double-triggering and led to a reduction of PTPINSP and VT. Similar results were found for ET and FM without leakage. Patient-ventilator interaction was disturbed in VH which favoured premature off-cycling. The high level of pressure support was associated with prolonged TLEXP when ET and FM were used, using VH tended to show the opposite effect. TLEXP was prolonged in the presence of leakage (IV-mode). This effect was partially corrected by using the NIV-mode. Conclusions: Augmenting the off-cycling criterion above the default setting (20-30% of peak inspiratory flow) improved patient-ventilator interaction in simulated COPD. The augmentation of the off-cycling criterion also led to premature cycling which was especially detected at low respiratory rate an when VH was used. The level of pressure support, the respiratory rate, leakage and the ventilation mode have to be considered when adjusting the off-cycling criterion.