Current opinion in critical care
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Curr Opin Crit Care · Feb 2001
ReviewClinical relevance of monitoring respiratory mechanics in the ventilator-supported patient: an update (1995-2000).
The introduction of mechanical ventilation in the intensive care unit environment had the merit of putting a potent life-saving tool in the physicians' hands in a number of situations; however, like most sophisticated technologies, it can cause severe side effects and eventually increase mortality if improperly applied. Assessment of respiratory mechanics serves as an aid in understanding the patient-ventilator interactions with the aim to obtain a better performance of the existing ventilator modalities. ⋯ Thanks to it, new ventilatory strategies and modalities have been developed. Finally, on-line monitoring of respiratory mechanics parameters is going to be more than a future perspective.
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Low tidal volume (4-8 mL/kg) during mechanical ventilation in adult respiratory distress syndrome is the standard of care. However, there are questions regarding the approach to setting positive end-expiratory pressure and the use of recruitment maneuvers in patients with adult respiratory distress syndrome. ⋯ Prone positioning has also become established a method of recruiting lung and improving PaO2 in those with adult respiratory distress syndrome. The data suggest that recruitment maneuvers in the prone position are most effective in improving PaO2 and that the positive end-expiratory pressure level required to sustain the improved PaO2 is less in the prone position than in the supine position.
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The basic mechanism of patient-ventilator asynchrony is the mismatching between neural inspiratory and mechanical inspiratory time. Alterations in respiratory drive, timing, respiratory muscle pressure, and respiratory system mechanics influence the interaction between the patient and the ventilator. None of the currently available partial ventilatory support modes are exempt from problems with patient-ventilator asynchrony. ⋯ The set inspiratory flow rate in the post-trigger phase for assist-control volume cycled ventilation affects patient-ventilator asynchrony. Likewise, the initial pressure rise time, the pressure support level, and the flow-threshold for cycling off inspiration for pressure support ventilation are important factors affecting patient-ventilator asynchrony. Current investigations have advanced our understanding in this area; however, its prevalence and the extent to which patient-ventilator asynchrony affect the duration of mechanical ventilation remain unclear.
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Subjective and objective measures of sleep quality indicate that the sleep of patients in the intensive care unit (ICU) is extraordinarily disturbed. Several studies spanning the past two decades have demonstrated that critically ill patients exhibit reduced sleep efficiency, reduced restorative sleep, and frequent arousals and awakenings. A number of potential sleep disrupters exist in the ICU environment, with noise being the predominant focus of investigation. ⋯ Medications, light, and frequent care-related activities can also interfere with a patient's ability to obtain good-quality sleep. Sleep disruption can have significant adverse consequences for critically ill patients, such as immune system compromise and respiratory abnormalities. Although several questions remain unanswered, including the impact of sleep disruption on the clinical outcome of patients in the ICU, there is a growing interest in developing new strategies to improve sleep quality.
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The term permissive hypercapnia defines a ventilatory strategy for acute respiratory failure in which the lungs are ventilated with a low inspiratory volume and pressure. The aim of permissive hypercapnia is to minimize lung damage during mechanical ventilation; its limitation is the resulting hypoventilation and carbon dioxide (CO2) retention. In this article we discuss the rationale, physiologic implications, and implementation of permissive hypercapnia. We then review recent clinical studies that tested the effect of various approaches to permissive hypercapnia on the outcome of patients with acute respiratory failure.