Chest
Effects of Initial Flow Rate and Breath Termination Criteria on Pressure Support Ventilation
Section snippets
PATIENTS AND METHODS
Thirty-three clinically stable, mechanically ventilated patients were studied. Initial data were collected while the patient was receiving his/her baseline mechanical ventilatory support (all patients were either on high levels of PS or on synchronized intermittent mandatory ventilation with lower levels of PS). Baseline data included: diagnosis, total minute ventilation determined by the ventilators exhaled volume monitor (MV), static respiratory system compliance (CRS, volume controlled tidal
RESULTS
Baseline characteristics of the 33 study patients are given in Table 1.
DISCUSSION
Several investigators have demonstrated that the spontaneous inspiratory effort which triggers a mechanically assisted breath does not cease with the delivery of that breath.7, 8, 9, 10 Thus, the potential for significant imposed ventilatory muscle loads exists if the mechanically assisted flows and volumes do not match the patient's desired flow pattern and tidal volume. Subjective dyspnea, as well as increased muscle energy demand, would appear to be a consequence of such imposed loads.8,11
ACKNOWLEDGMENT
The authors are indebted to Mrs. Janet Johns for her secretarial expertise.
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2008, ChestCitation Excerpt :A constant or square inspiratory flow waveform was applied with the IMV breaths. For PSV, the “% rise” setting on the ventilator (ie, the control to adjust the ventilator flow-rate output during inhalation and, thus, the rate of pressure rise, which results from the interaction of ventilator flow rate output and patient inspiratory flow rate demand10) ranged from 60 to 80%, and the expiratory sensitivity setting (“Esens”) or PSV breath-termination criteria was 25%. The levels of PSV, PEEP, fraction of inspiratory oxygen (Fio2), carbon dioxide elimination, and hemoglobin oxygen saturation were comparable for patients at all sites at the time of enrollment into the study (Table 1).