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机械通气:急性监护设置中的非侵入性方法

Mechanical Ventilation: Noninvasive Strategies in the Acute Care Setting
Disclosures
Neil R. Maclntyre, MD
Introduction
　　Noninvasive ventilation (NIV) is the technique of supplying positive pressure ventilatory support to the airways through masks attached to a patient's nose or mouth. This support can be in the form of a constant positive airway pressure throughout the ventilatory cycle (eg, continuous positive airway pressure [CPAP]), or it can deliver inspiratory pressure above expiratory pressure as a form of ventilatory support. This latter strategy is sometimes referred to as bilevel positive airway pressure (BIPAP).[1]
　　CPAP can be supplied by attaching a mask to a conventional intensive care unit (ICU) ventilator or by using a simpler device designed solely for this purpose. CPAP will raise functional residual capacity (which may reduce the inspiratory work to breathe in some disease states -- see below), and it can also be used to "splint open" collapsing/obstructed upper airways in disease states such as obstructive sleep apnea.
　　BIPAP can also be supplied by attaching a mask to a conventional ICU ventilator and generally using a time cycled, pressure targeted mode (pressure assist control). The flow cycled, pressure targeted mode, pressure support, is not appropriate under these circumstances because mask leak may disrupt the ICU ventilator breath cycling algorithm. Simpler ventilators designed solely for mask application generally also supply pressure assist control. These devices often also provide pressure support by using special leak compensation mechanisms. BIPAP can not only accomplish the goals of CPAP noted above but can also further reduce inspiratory muscle loads through the application of additional inspiratory pressure.
　　One of the major conceptual advantages to NIV (both CPAP and BIPAP) is that the need for endotracheal intubation is avoided. This, in turn, should translate into better comfort (and, thus, less sedation) as well as a reduced risk of ventilator-associated pneumonia (VAP) and tracheal injury.[1]
　　NIV in Acute Respiratory Failure
　　Acute Heart Failure
　　Invasive Ventilator Weaning
Conclusion
　　NIV is an attractive alternative to endotracheal intubation in patients needing positive pressure respiratory support. Data are strong that early removal of endotracheal tubes improves comfort, reduces risk of VAP, and reduces risk of airway trauma. NIV, however, can only provide limited levels of respiratory support and does not provide airway protection or ready access for airway toilet. The strongest evidence supporting its use is in patients with acute exacerbations of COPD. Fewer data exist to support the use of NIV in other forms of acute respiratory failure. In acute heart failure, CPAP by NIV has been shown in multiple studies to improve cardiac physiology as well as improve oxygenation and reduce inspiratory work. Whether BIPAP offers additional benefit, however, is unclear. In patients with prolonged ventilator dependence but with adequate airway protection capabilities, NIV has been explored in 2 areas. First, in early extubation failures, NIV has been shown to "buy time" for reversible issues. However, in more progressive extubation failure, NIV has not been of benefit. Second, in patients known to still require ventilatory assistance, early extubation with planned replacement by NIV has been evaluated in several studies but results have been inconsistent.
References
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3. American Association for Respiratory Care Consensus Group. Noninvasive mechanical ventilation. Respir Care. 1997;42:364-369.
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