Resp Care
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In the critical care setting, usually the most important outcome is survival. However, this is not the only important outcome of critical care. There are increasing data that the patient's quality of life and functional status can be affected long after an intensive care unit stay, and some data suggest that mechanical ventilation strategies could influence those outcomes. ⋯ To deliver effective, cost-effective, and patient-centered care, critical-care clinicians must consider outcomes other than survival. These outcomes include such diverse concepts as quality of life, functional status, and neuropsychological function. This review addresses theoretical and practical challenges to measuring and interpreting those other outcomes.
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There is increasing appreciation that lung-protective strategies are beneficial in patients with acute respiratory distress syndrome. Using low tidal volume in these patients improves survival. However, low tidal volume ventilation may promote alveolar de-recruitment. ⋯ A variety of approaches have been used as recruitment maneuvers, including increasing the level of positive end-expiratory pressure, sustained inflation maneuvers, sigh breaths, spontaneous breathing, and others. There have been a number of recent reports describing improvements in arterial oxygenation with the use of recruitment maneuvers. However, the impact of recruitment maneuvers on patient-important outcomes such as survival is unknown.
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Application of positive end-expiratory pressure (PEEP) in acute lung injury patients under mechanical ventilation improves oxygenation and increases lung volume. The effect of PEEP is to recruit lung tissue in patients with diffuse lung edema. This effect is particularly important in patients ventilated with low tidal volumes. ⋯ In patients with acute respiratory distress syndrome in whom the lungs have been near-optimally recruited by PEEP and tidal volume, the use of recruitment maneuvers as adjuncts to mechanical ventilation remains controversial. The application of PEEP in patients with unilateral lung disease may be detrimental if PEEP hyperinflates normal lung regions, thus directing blood flow to diseased lung regions. In patients with air flow limitation and lung hyperinflation, the application of additional external PEEP to compensate for intrinsic PEEP and flow limitation frequently decreases the inspiratory effort to initiate an assisted breath, thus decreasing breathing work load.
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Alveolar (and thus arterial) P(O2) and P(CO2) clearly depend on minute ventilation. However, we need to balance gas exchange goals against the risk of overstretching, especially of the healthier regions of the lung. The plateau pressure is probably the best easily-obtained marker of the risk of stretch in the lung, and a commonly quoted threshold is 30--35 cm H(2)O, the normal maximum transalveolar pressure at total lung capacity. ⋯ In addition, the small V(T) of HFV prevents excessive end-inspiratory distention. Although considerable clinical data support the use of HFV in pediatric patients at risk for ventilator-induced lung injury, there are few data from adults. Whether HFV will prove valuable in well-designed open lung strategies in the adult population still has to be determined.