Resp Care
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Acute lung injury/acute respiratory distress syndrome is a syndrome of low respiratory compliance. However, longstanding knowledge of applied respiratory mechanics and refined imaging techniques have shown that this is clearly an oversimplified view. ⋯ These basic measurements, once the domain of applied physiologists only, are now available to aid clinicians to choose the appropriate ventilator settings to promote lung recruitment and avoid injury during lung-protective ventilatory strategies. High-resolution lung imaging and bedside recording of physiologic variables are important tools for clinicians who want to deliver specialized care to improve the outcome of critically ill patients in acute respiratory failure.
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Pressure support ventilation (PSV) is a commonly used mode. It is patient-triggered, pressure-limited, and (normally) flow-cycled. Triggering difficulty occurring during PSV is usually due to intrinsic positive end-expiratory pressure. ⋯ Patient-ventilator dyssynchrony may occur during PSV if the flow at which the ventilator cycles to exhalation does not coincide with the termination of neural inspiration. The newer generation ventilators offer clinician-adjustable flow-termination during PSV. Ventilator waveforms may be useful to appropriately adjust the ventilator during PSV.
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The interaction of a mechanical ventilator and the human cardiovascular system is complex. One of the most important effects of positive-pressure ventilation (PPV) is that it can decrease venous return. PPV also alters right- and left-ventricular ejection. ⋯ Understanding and managing these complex and often opposing interactions in critically ill patients is facilitated by analysis of hemodynamic and ventilator waveforms at the bedside. The relationship of PPV to changes in the arterial pressure waveform gives important information regarding appropriate fluid and vasopressor treatment. This article focuses on effects of respiratory pressures on hemodynamics and considers how cardiac pressures can be transmitted to the airway and cause ventilator malfunction.
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Dual-control ventilation modes were introduced with the goal of combining the advantages of volume-control ventilation (constant minute ventilation) and pressure-control ventilation (rapid, variable flow). Dual-control ventilation modes have gained popularity despite little evidence to support routine use. ⋯ Inspecting the waveforms will lead clinicians to the realization that dual-control does not guarantee a set tidal volume and that variability in delivered tidal volume is greater with dual-control than with pressure control. These realizations have important implications for low-tidal volume strategies.
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Graphical waveforms have become ubiquitous in clinical care. Using and understanding pictures and symbols is a daily activity. Humans are neurologically equipped to understand symbolic information and have done so for millennia. ⋯ Didactic study, frequent viewing, and understanding of the background of the artist (artistic context) are needed to fully appreciate art. Using waveforms to care for patients requires understanding of the clinical context under which they are obtained, factors that affect their creation, and artifacts that interfere with interpretation. This article summarizes the presentation and discussions at this Journal Conference on ventilator waveforms in relation to lung and chest wall compliance, resistance, carbon dioxide kinetics, hemodynamics, specific modes of ventilation, specific lung diseases, and ventilator-weaning.