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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Invasive mechanical ventilation can be lifesaving for patients with acute respiratory failure, but numerous complications have been identified. Therefore, once clinical improvement has occurred, emphasis is placed on quickly weaning (ie, liberating) the patient from mechanical ventilation. Weaning can be subdivided into 2 components: readiness testing and progressive withdrawal. ⋯ Recent insights into the pathophysiology of weaning failure have provided a framework for identifying potentially correctable limiting factors. Randomized controlled trials suggest that several approaches to progressive withdrawal may be acceptable, though only a minority of patients require progressive withdrawal. Emerging evidence indicates that protocol-directed weaning, driven by respiratory therapists and intensive care nurses, can improve outcome.
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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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Increased understanding of the mechanisms and effects of acute respiratory failure has not been accompanied by more precise criteria by which the clinician can determine when intubation should be carried out and invasive positive-pressure ventilation (IPPV) instituted in a given patient. The indications traditionally offered in reviews and textbooks have tended to be either so broad as not to be very helpful in an individual case, or of questionable clinical relevance and too cumbersome for practical use. This review updates the indications for IPPV in adult patients with acute respiratory failure by examining available evidence from clinical trials and by considering new management alternatives that have become available in the last 20 years. ⋯ However, in other settings of acute hypoxemic respiratory failure, such as acute lung injury and acute respiratory distress syndrome, this has not been shown. The use of IPPV may improve outcomes in patients with severe cardiogenic shock. However, IPPV has not proven to be beneficial in traumatic brain injury and flail chest, in the absence of other indications.
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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.