Resp Care
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One of the most important aspects of caring for a critically ill patient is monitoring. Few would disagree that the most essential aspect of monitoring is frequent physical assessments. Complementing the physical examination is continuous monitoring of heart rate, respiratory rate, and blood oxygen saturation measured via pulse-oximetry, which have become the standard of care in intensive care units. ⋯ Based on the available literature, it seems reasonable to use continuous capnography, for at least a subset of critically ill patients, to ensure integrity of the endotracheal tube and other ventilatory apparatus. However, at this point definitive data are not yet available to clearly support continuous capnography for optimizing mechanical ventilatory support. We hope that as new data become available, the answer to this capnography question will become clear.
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Ventilator-associated pneumonia (VAP) significantly increases intensive care unit morbidity, mortality, and costs. VAP is thought to be caused by bacterial entry into injured airways, which produces tracheobronchitis that evolves into diffuse pneumonia. The use of aerosolized antibiotics is conceptually attractive, especially when the infection is early and limited to the airway epithelium. ⋯ The clinical evidence for aerosolized antibiotics to prevent VAP is weak but suggestive. Concerns about the high cost, possible development of antibiotic resistance, and other potential risks of aerosolized antibiotics led several evidence-based consensus groups to recommend against routine use of aerosolized antibiotics for VAP prevention until better data are available. Importantly, the clinical evidence that aerosolized antibiotics can treat established VAP is negative, and multiple consensus groups recommend against treating established VAP with aerosolized antibiotics.
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Positive end-expiratory pressure (PEEP) and inspired oxygen fraction (F(IO(2))) are the primary means of improving P(aO(2)) during mechanical ventilation. Patients with acute respiratory distress syndrome (ARDS) typically present with a large intrapulmonary shunt, which makes even high F(IO(2)) ineffective in improving P(aO(2)). ⋯ The improved survival found in the National Institutes of Health's ARDS Network low-tidal-volume study may suggest that their PEEP/F(IO(2)) titration tables represent the best method for adjusting these variables. Based upon an extensive literature review of PEEP and respiratory system mechanics in ARDS, we conclude that: (1) for most patients the therapeutic range of PEEP is relatively narrow, so the ARDS Network PEEP/F(IO(2)) strategy is reasonable and supported by high-level evidence, (2) how best to adjust PEEP to prevent or ameliorate ventilator-associated lung injury is unknown and still under investigation, and (3) in a small subset of patients with severe lung injury and/or abnormal chest-wall compliance, highly individualized titration of PEEP, based upon the respiratory-system pressure-volume curve, PEEP/tidal-volume titration grids, or a recruitment maneuver and a PEEP decrement trial is a reasonable alternative.
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Airway pressure-release ventilation (APRV) is a mechanical ventilation strategy that is usually time-triggered but can be patient-triggered, pressure-limited, and time-cycled. APRV provides 2 levels of airway pressure (P(high) and P(low)) during 2 time periods (T(high) and T(low)), both set by the clinician. APRV usually involves a long T(high) and a short T(low). ⋯ Other ventilation modes also promote spontaneous breaths, but at overall lower end-inflation transpulmonary pressure. There is a dearth of data on what would be the optimal APRV inspiratory-expiratory ratio, positive end-expiratory pressure, or weaning strategy. The few clinical trials to date indicate that APRV provides adequate gas exchange, but none of the data indicate that APRV confers better clinical outcomes than other ventilation strategies.
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Traditional mechanical ventilation is provided with either a constant volume or constant pressure breath. In recent years, dual-control (adaptive pressure control) has been introduced in an attempt to combine the attributes of volume ventilation (constant tidal volume and minute ventilation) with the attributes of pressure ventilation (rapid, variable flow and reduced work of breathing). Adaptive pressure control is a pressure-controlled breath that utilizes closed-loop control of the pressure setting to maintain a minimum delivered tidal volume. ⋯ While adaptive pressure control can guarantee a minimum tidal volume, it cannot guarantee a constant tidal volume. One concern is that the ventilator cannot distinguish between improved pulmonary compliance and increased patient effort. Clinicians should be aware of the limitations of adaptive pressure control and understand when other breath delivery techniques are more suitable.