KEY POINTS
• To reduce the morbidity and mortality rates of treatment with endotracheal intubation, noninvasive positive pressure ventilation (NIPPV) was developed in the late 1980s as an alternative to endotracheal intubation. Since then, many studies have compared the efficacy of NIPPV to conventional medical therapies for all causes of acute respiratory failure (ARF).
• During NIPPV, a mask attached to a ventilator machine is placed over the patient's mouth and/or nose to deliver positive pressure to the patient's airway. The provider should titrate NIPPV to meet the desired physiologic end points.
• Randomized controlled trials have shown that this treatment improves patient outcomes with ARF secondary to COPD exacerbations with hypercapnia, CPE, and asthma exacerbations.
• Patients with other forms of ARF, such as nosocomial pneumonia, ARDS, and aspiration pneumonitis, have not shown a decrease in morbidity and mortality with the use of NIPPV but have shown a decrease in the need for endotracheal intubation.
• Studies are ongoing to answer other questions related to NIPPV use in patients with forms of ARF as well as to investigate using NIPPV as a bridge to extubation.
Acute respiratory failure (ARF) is one of the most common diagnoses in adults admitted to an ICU. In one study, Vincent and colleagues found that 32% of patients had ARF on admission to the ICU and another 24% developed the condition during their stay.1 Patients with ARF often require endotracheal intubation and mechanical ventilation. The complications of these procedures in combination with risks associated with the underlying disease process lead to high morbidity and mortality rates in this patient population. In critically ill patients with ARF, the mortality rate is between 40% and 65%.1 Complications of endotracheal intubation and mechanical ventilation include dental damage, oropharyngeal damage, corneal abrasions, vocal cord damage, tracheal damage, pneumothorax, pulmonary aspiration, ventilator-associated pneumonia, alveolar damage, and bronchospasm, among others.
To reduce the morbidity and mortality rates, noninvasive positive pressure ventilation (NIPPV) was developed in the late 1980s as an alternative to endotracheal intubation.2 Since then, many studies have compared the efficacy of NIPPV to conventional medical therapies (CMTs) for ARF. This article details the causes of ARF and the role NIPPV plays with each; contraindications for the use of NIPPV; complications of NIPPV; how to initiate and titrate NIPPV therapy; how to reevaluate a patient on NIPPV; and how to determine when a patient has not adequately responded to NIPPV therapy and will require endotracheal intubation with mechanical ventilation.
MECHANICS OF NIPPV
During NIPPV, a mask attached to a ventilator machine is placed over the patient's mouth and/or nose to deliver positive pressure to the patient's airway (Figure 1). NIPPV ventilates and oxygenates the lungs and helps to maintain upper airway patency. Three common methods are used to deliver NIPPV breaths. The first technique is continuous positive airway pressure (CPAP), in which the machine delivers air at a constant pressure during both inspiration and expiration. In pressure support mode, the machine delivers air at a set pressure each time the patient takes a breath. Lastly, during bilevel positive airway pressure (BiPAP), the machine delivers different pressures during inspiration and expiration. The NIPPV display is depicted in Figure 2.
NIPPV reduces the amount of effort required by a patient during breathing by decreasing the amount of support required by the diaphragm and accessory muscles. This decrease in required effort diminishes the amount of inspiratory energy the patient must exert and aids ventilation by increasing both tidal volume and minute ventilation, which acts to decrease the patient's PaCO2. NIPPV also provides positive end-expiratory pressure, which opens flooded or collapsed alveoli, thus improving atelectasis and oxygenation. NIPPV also improves cardiac output by decreasing the left ventricular afterload.3
CAUSES OF ARF AND THE ROLE OF NIPPV
COPD exacerbations Acute exacerbations of chronic obstructive pulmonary disease (COPD) are one of the most common causes of ARF encountered in ICUs. Patients with COPD are frequently admitted to the hospital with hypercapnic respiratory failure. Hypercapnia results from worsening ventilation that prevents the patient's body from ridding itself of a sufficient amount of carbon dioxide. As carbon dioxide builds up in the blood, it causes respiratory acidosis likely spurred by worsening lung function, bronchospasm from a worsened obstructive process, pneumonia-producing secretions, or pulmonary edema. The end result is over-fatigued respiratory muscles that cause ventilatory failure.
Strong evidence exists to support the use of NIPPV in patients with acute exacerbations of COPD. Ram and colleagues, who reviewed 14 randomized controlled trials (RCTs) conducted between 1993 and 2004 involving 758 patients, found that mortality was reduced by 48% with NIPPV compared to CMT.4 They also found that NIPPV reduced the risk of endotracheal intubation by 59%. Length of stay was reduced by an average of 3 days, and morbidity and mortality were significantly reduced with an overall risk reduction of 62%.4