Acute respiratory failure (ARF) refers to a severe deterioration in gas exchange that may require mechanical ventilation for life support. Instituted when conservative treatment fails, mechanical ventilation aims to improve the pathophysiology of ARF, reduce the work of breathing, and ameliorate dyspnea; concomitant pharmacologic intervention is directed at correcting the condition that resulted in ARF. Traditionally, an endotracheal tube is inserted into the trachea to deliver positive pressure to the patient's lungs. Potential complications and discomfort associated with placing this artificial airway have confined the use of mechanical ventilation to the most severe forms of ARF.
Injury to the upper airways can occur at the point of contact between the mucosa and the endotracheal tube or cuff and can result in ulceration, edema, and hemorrhage, with potential stenosis. Most importantly, however, the endotracheal tube directly places patients at significant risk for developing life-threatening nosocomial infections— mainly ventilator-associated pneumonia and sinusitis.155
Noninvasive ventilation (NIV) includes various techniques of augmenting alveolar ventilation without an endotracheal airway. The theoretic advantages of this approach include avoiding the complications associated with endotracheal intubation, improving patient comfort, and preserving airway defense mechanisms, speech, and swallowing.103 Furthermore, NIV provides greater flexibility in instituting and removing mechanical ventilation. Noninvasive methods include external negative pressure, chest wall oscillation, and positive-pressure ventilation administered through a mask, which is the subject of this article.
The origin of positive-pressure ventilation dates back to the creation of man (Genesis 2:7):
And the Lord God formed man of the dust of the ground, and breathed into his nostrils the breath of life, and man became a living soul.
It was not until 1935, however, that Barach131416171819 reported a series of studies involving a powered mechanical ventilator to deliver continuous positive airway pressure (CPAP) through a face mask to patients with pulmonary edema and other forms of respiratory failure. With the evolution of aeronautic engineering during World War II, the technical knowledge was generated to allow development of modern mechanical ventilators. By the early 1960s, the endotracheal tube became widely accepted as the exclusive interface to deliver mechanical tidal breaths to patients with ARF.
In the late 1970s and early 1980s, two methods of noninvasive positive-pressure ventilation, using a facial or nasal mask, were introduced into clinical practice—CPAP improved oxygen exchange in patients with hypoxemic ARF (Table 1) and intermittent positive-pressure ventilation (IPPV) rested the respiratory muscles of patients with chronic respiratory failure resulting from neuromuscular disease and chronic obstructive pulmonary disease (COPD). In the early 1990s, encouraging results of a pilot study153 stimulated investigation of NIV with IPPV in patients with ARF (Table 2). In this article, clinical application of NIV using CPAP alone is referred to as mask CPAP, and NIV using IPPV with or without CPAP as noninvasive (intermittent) positive-pressure ventilation (NPPV). The aim of this article is to provide the reader with a systematic review of the literature on applying NIV in various forms of hypercapnic and hypoxemic ARF. Under headings for each disease state causing ARF, a description of the underlying pathophysiology is followed by a review of physiologic data (when available) explaining the mechanisms of action of NIV. To assess the risks and benefits of NIV versus conventional management, data are provided on complications of mechanical ventilation via endotracheal intubation. A critical review of clinical studies is followed by specific recommendations. Because the correct implementation and monitoring of NIV in patients with ARF are critical to its success, methodology is covered in detail. Finally, advantages and disadvantages of NIV in ARF are discussed.
