Resp Care
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Since the early 1970s there has been an ongoing debate regarding the wisdom of promoting unassisted spontaneous breathing throughout the course of critical illness in patients with severe respiratory failure. The basis of this debate has focused on the clinical relevance of opposite problems. Historically, the term "disuse atrophy" has described a situation wherein sustained inactivity of the respiratory muscles (ie, passive ventilation) results in deconditioning and weakness. ⋯ Regardless, the clinical implications of this research strongly suggest that passive mechanical ventilation should be avoided whenever possible. However, promotion of unassisted spontaneous breathing in the acute phase of critical illness also may carry a substantial risk of respiratory muscle injury and weakness. Use of mechanical ventilation modes in a manner that induces spontaneous breathing effort, while simultaneously reducing the work load on the respiratory muscles, is probably sufficient to minimize both problems.
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Optimizing patient-ventilator synchrony is essential in managing patients who require prolonged mechanical ventilation in the long-term acute-care hospital. Inadequate synchrony can increase work of breathing, cause patient discomfort, and delay both weaning and general rehabilitation. Achieving optimal synchrony in the long-term acute-care hospital depends on a number of factors, including adjusting ventilator settings in response to improving lung function; adjusting psychotropic medications to control delirium, anxiety, and depression; and ensuring there is a well positioned correctly sized tracheostomy tube in the airway. The purpose of this review is to provide an update on issues pertinent to patient-ventilator synchrony in the LTACH setting.
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Patient-ventilator synchrony is a common problem with all patients actively triggering the mechanical ventilator. In many cases synchrony can be improved by vigilant adjustments by the managing clinician. ⋯ Proportional assist ventilation (PAV) and neurally adjusted ventilatory assist (NAVA) were both developed to improve patient-ventilator synchrony by proportionally unloading ventilatory effort and turning control of the ventilatory pattern over to the patient. This paper discusses PAV's and NAVA's theory of operation, general process of application, and the supporting literature.
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Patient-ventilator interaction has been the focus of increasing attention from both manufacturers and researchers during the last 25 years. There is now compelling evidence that passive (controlled) mechanical ventilation leads to respiratory muscle dysfunction and atrophy, prolonging the need for ventilatory support and predisposing to a number of adverse patient outcomes. Although there is consensus that the respiratory muscles should retain some activity during acute respiratory failure, patient-ventilator asynchrony is now recognized as a cause of ineffective ventilation, impaired gas exchange, lung overdistention, increased work of breathing, and patient discomfort. ⋯ The respected authorities on mechanical ventilation who participated in this conference differed in the modes they preferred but agreed that proper understanding and use according to the individual patient's needs are more important than which mode is chosen. Conference participants discussed the determinants, manifestations, and epidemiology of patient-ventilator asynchrony, and described and compared several ventilation modes aimed specifically at preventing and ameliorating it. The papers arising from these discussions represent the most thorough examination of this important aspect of respiratory care yet published.
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There has been a dramatic increase in the number and complexity of new ventilation modes over the last 30 years. The impetus for this has been the desire to improve the safety, efficiency, and synchrony of ventilator-patient interaction. Unfortunately, the proliferation of names for ventilation modes has made understanding mode capabilities problematic. ⋯ These control systems are designed to serve the 3 primary goals of mechanical ventilation: safety, comfort, and liberation. The basic operations of these schemes may be understood by clinicians without any engineering background, and they provide the basis for understanding the wide variety of ventilation modes and their relative advantages for improving patient-ventilator synchrony. Conversely, their descriptions may provide engineers with a means to better communicate to end users.