Cruz Monica R, Camilo Luciana M, Paula Luis Felipe S C, Japiassú Andre M, Beda Alessandro, Carvalho Alysson R, Bozza Fernando A, Medeiros Denise M
Laboratory of Clinical Research in Intensive Care Medicine, National Institute of Infectious Disease, Oswaldo Cruz Foundation, Rio de Janeiro, Brazil.
Laboratory of Respiration Physiology, Carlos Chagas Filho Institute of Biophysics, Universidade Federal do Rio de Janeiro, Brazil.
Respir Care. 2014 Dec;59(12):1888-94. doi: 10.4187/respcare.02853. Epub 2014 Aug 12.
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.
Fourteen invasively mechanically ventilated subjects were prospectively studied. PS was adjusted at 20 cm H2O and sequentially reduced to 15, 10, and 5 cm H2O. Arterial blood gas analysis and pressure at 0.1 s after the onset of inspiration (P0.1) were measured at each PS level. Airway and esophageal pressure and air flow were continuously recorded. Peak inspiratory flow, tidal volume (VT), 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 VT, peak inspiratory flow, and breathing frequency from ∼ 60 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.
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 VT between PS levels were observed (P > .15). Additionally, a significant increase in P0.1, PTP, and breathing frequency (P < .01) and a reduction in VT (P < .001) were observed with PS reduction.
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.
有证据表明，在压力支持通气（PSV）期间，增加呼吸模式的外在（即呼吸机产生的）逐次呼吸变异性（BBV）可改善呼吸功能。如果BBV本身有益，那么选择能使其最大化的PS水平可被视为传统PSV的一种有效策略。在本研究中，我们评估了不同PS水平对急性病机械通气患者内在BBV的影响，以确定PS水平与BBV幅度之间是否存在显著关系。
对14名有创机械通气患者进行前瞻性研究。PS先调整为2０cmH₂O，然后依次降至15、10和5cmH₂O。在每个PS水平测量动脉血气分析和吸气开始后0.1秒时的压力（P0.1）。持续记录气道和食管压力以及气流。逐次计算吸气峰流速、潮气量（VT）、呼吸频率和压力-时间乘积（PTP）。通过在每个PS水平连续约60个呼吸周期的VT、吸气峰流速和呼吸频率时间序列的变异系数评估呼吸模式变异性。应用重复测量的一般线性模型，将PS作为独立因素。显著性水平设定为0.05。
尽管所有测量变量存在较大个体差异（P < 0.001），变异系数低至30%，且未观察到PS水平之间吸气峰流速、呼吸频率和VT变异系数的显著差异（P > 0.15）。此外，随着PS降低，观察到P0.1、PTP和呼吸频率显著增加（P < 0.01），VT降低（P < 0.001）。
尽管随着PS降低自主活动显著增加，但BBV不受PS水平影响，所有评估参数的BBV均低至30%。
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