Effects of Different Levels of Pressure Support on Intra-Individual Breath-to-Breath Variability

Abstract

BACKGROUND: Evidence exists that during pressure support ventilation (PSV), the addition of an extrinsic (ie, ventilator-generated) breath-to-breath variability (BBV) of breathing pattern improves respiratory function. If BBV is beneficial per se, choosing the PS level that maximizes it could be considered a valid strategy for conventional PSV. In this study, we evaluated the effect of different PS levels on intrinsic BBV in acutely ill, mechanically ventilated subjects to determine whether a significant relationship exists between PS level and BBV magnitude. METHODS: Fourteen invasively mechanically ventilated subjects were prospectively studied. PS was adjusted at 20 cm H 2 O and sequentially reduced to 15, 10, and 5 cm H 2 O. Arterial blood gas analysis and pressure at 0.1 s after the onset of inspiration (P 0.1 ) were measured at each PS level. Airway and esophageal pressure and air flow were continuously recorded. Peak inspiratory flow, tidal volume (V T ), breathing frequency, and pressure-time product (PTP) were calculated on a breath-by-breath basis. The breathing pattern variability was assessed by the coefficient of variation of the time series of V T , peak inspiratory flow, and breathing frequency from ϳ60 consecutive breath cycles at each PS level. A general linear model for repeated measures was applied, with PS as an independent factor. A significance level of .05 was considered. RESULTS: Despite a large inter-individual difference in all measured variables (P < .001), the coefficient of variation was as low as 30%, and no significant differences in the coefficient of variation of peak inspiratory flow, breathing frequency, and V T between PS levels were observed (P > .15). Additionally, a significant increase in P 0.1 , PTP, and breathing frequency (P < .01) and a reduction in V T (P < .001) were observed with PS reduction. CONCLUSIONS: Despite a significant increase in spontaneous activity with PS reduction, BBV was not influenced by the PS level and was as low as 30% for all evaluated parameters.

Synchronized intermittent mandatory ventilation with volume guarantee and pressure support in neonates: Detailed analysis of ventilator parameters

“…In adults, progressively decreasing PS levels were associated with increasing breathing rate but no change in pCO 2 12 and similar findings have also been reported in neonates. 10 For adults, a proprietary automated weaning protocol (SmartCare™; Dräger) has been developed to adjust PS level based on respiratory rate and tcCO 2 and it has been shown to reduce the duration of mechanical ventilation.…”