Respiratory care clinics of North America
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Maintaining optimal lung recruitment has a marked effect on the outcome of patients who suffer from ARDS. RMs superimposed on mechanical ventilation have the potential to recruit atelectatic lungs in the course of general anesthesia; however, the physiologic benefits are less evident in ARDS patients who are ventilated at low VT values and high PEEP levels. ⋯ Although RMs are transient, they may be associated with complications such as hypotension, bradycardia, and barotrauma. Moreover, further studies are needed to compare the efficacy of periodic high-pressure RMs that are superimposed on mechanical ventilation with ventilation using high PEEP levels and low VT values without RMs in patients who have early ARDS after initial hemodynamic stabilization.
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Respir Care Clin N Am · Jun 2002
ReviewProne positioning in patients with acute respiratory distress syndrome.
Acute respiratory distress syndrome (ARDS) is a severe form of respiratory failure that is characterized by marked hypoxemia, bilateral infiltrates on chest radiograph, and no clinical evidence of left ventricular failure. Mechanical ventilation with positive end-expiratory pressure (PEEP) is a cornerstone therapy for ARDS patients. ⋯ Despite encouraging results, however, the use of prone positioning is not widely accepted as an adjunct to therapy in hypoxemic patients because, aside from temporarily improving gas exchange, it does not seem to affect the outcome of these patients. This article reviews the rationale for using prone positioning in ARDS patients who require intubation and mechanical ventilation.
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Respir Care Clin N Am · Jun 2002
ReviewHigh-frequency mechanical ventilation principles and practices in the era of lung-protective ventilation strategies.
The term high-frequency ventilation is used to describe a heterogeneous group of ventilation modes that are characterized by high respiratory frequencies and low tidal volumes. The increasing understanding of the pathogenesis of VILI, including concepts such as volutrauma and atelectrauma, has led to a renewed interest in the role of HFV in lung-protective ventilation strategies. Inherent to many modes of HFV are low tidal volumes and small pressure swings during the respiratory cycle, which allow for higher mean airway pressures than those safely achieved with CMV. ⋯ Early studies of applying HFO in ARDS patients have demonstrated its safety and benefit in terms of oxygenation. Additionally, limited data exist on the comparison between HFO and CMV in this patient population; however, encouraging preliminary results have been reported. The optimum strategy for the application of HFV, including the timing of HFV initiation, remains unclear.
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There has been increasing recognition that mechanical ventilation can cause acute parenchymal lung injury (ventilator-induced lung injury, or VILI) in addition to the more widely recognized forms of barotrauma. Furthermore, in patients with acute lung injury, this type of injury may cause considerable morbidity and mortality. ⋯ In patients with acute asthma, chronic obstructive pulmonary disease, or acute lung injury, however, accepting abnormal blood-gas tensions, particularly an elevated PaCO2 (permissive hypercapnia), to improve survival and reduce complications is frequently necessary. Extensive experience has shown that ventilated patients usually tolerate moderate hypercapnia and frequently some degree of hypoxemia in the absence of shock, anemia, severe cardiac disease, or other contraindications.
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In laboratory models, PLV is clearly more effective than conventional ventilation alone; however, this advantage has not been observed in any human study. The reasons for this are unclear, but the approach to ventilation during PLV may have been inappropriate. HFO may require further study or perhaps PLV should be combined with nitric oxide or some other vasoactive agent. ⋯ Kandler et al. recently demonstrated better gas exchange that was sustained for a longer period in lavage-injured piglets when a perfluorocarbon was aerosolized. This preliminary result demonstrates that there are other options for the delivery of perfluorocarbons in the management of critically ill patients. Based on the failure of the two trials in adult ARDS patients, however, a long time may pass before another human PLV trial is undertaken.