Noninvasive ventilation (NIV) has assumed an important role in the intensive care unit (ICU), with increasing use during the past 15 years. It is now considered the ventilatory mode of first choice for such forms of acute respiratory failure ( Table 7-1 ). Multiple randomized controlled trials have demonstrated that NIV improves outcomes in these forms of respiratory failure. Improved outcomes include avoidance of intubation and reduced morbidity and mortality compared with conventional therapy including intubation. In addition, the role of NIV is expanding as more studies are completed in other forms of respiratory failure. There are encouraging results from trials evaluating NIV use in postoperative respiratory failure and preoxygenation of patients with hypoxemic respiratory failure before intubation in the ICU. The results are less clear in other forms of respiratory failure such as severe asthma, pneumonia, and acute lung injury (ALI)/acute respiratory distress syndrome (ARDS) as well as in postextubation respiratory failure in patients with non–chronic obstructive pulmonary disease (COPD).
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Selecting Patients for Noninvasive Ventilation
The first question that should be addressed when selecting patients for NIV is whether the patient needs ventilatory support. Such patients usually have moderate to severe respiratory distress, signs of increased work of breathing such as tachypnea, increased use of accessory muscles, or abdominal paradox. Arterial blood gases should be obtained before starting NIV to assess the severity of the gas exchange derangement (particularly partial pressure of arterial carbon dioxide [Paco 2 ]) and to establish a baseline for comparison after the first 1 to 2 hours. Acutely ill patients should be monitored initially in an ICU or step-down unit to ensure that the patient is improving and tolerating the mask. Trials have shown that the response at the 1- to 2-hour time point is highly predictive of subsequent outcome; patients improving at this point are likely to succeed, but those failing to respond are likely to fail. Risk factors for failure after 2 hours of NIV are listed in Table 7-2 .
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Contraindications to Noninvasive Ventilation
When the need for ventilatory assistance is established, candidates for NIV should be screened for possible contraindications. NIV is contraindicated in patients with cardiopulmonary arrest because there is no time to place a mask and make adjustments. Any patient in shock requiring more than low doses of vasopressors is not a good candidate, nor is the patient with a large acute myocardial infarction, uncontrolled arrhythmias or cardiac ischemia, or a large upper gastrointestinal bleed that is threatening the upper airway. Uncooperative and agitated patients and those with severe claustrophobia are unlikely to tolerate the mask. Patients with copious secretions, impaired swallowing, and frequent vomiting are at risk for aspiration and are poor candidates. Recent upper gastrointestinal surgery is also a relative contraindication because of the risk for abdominal distension and suture line rupture, although there have been some reports of successful use of NIV in these patients. Upper airway obstruction due to epiglottitis or angioedema is best treated with intubation to avoid progression to complete airway obstruction and the need for emergent cricothyrotomy, although upper airway obstruction due to glottic edema after extubation may respond well. Impaired mental status is a relative contraindication, with one of the major concerns being the patient’s inability to remove the mask in the event of vomiting. However, hypercapnic coma in patients with COPD exacerbations should not be considered a contraindication, and one trial has shown good outcomes with NIV use in these patients ( Table 7-3 ).
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Applications of Noninvasive Ventilation in the Intensive Care Unit
NIV has been tried for many types of respiratory failure in the ICU. However, the evidence to support these applications varies depending on the diagnosis or circumstance. Table 7-4 lists the most common applications and the levels of evidence supporting them. In the following, we discuss the evidence supporting the various applications in more detail, starting with those supported by the strongest evidence.
| Strength of Recommendation ∗ | Indication for NIV | Quality of Evidence † |
|---|---|---|
| Strong | COPD exacerbations | A |
| Acute cardiogenic pulmonary edema | A | |
| Immunocompromised states | A | |
| Facilitating extubation in COPD | A | |
| Intermediate | Postoperative respiratory failure | B |
| Preoxygenation in hypoxemic respiratory failure | B | |
| Facilitation of flexible bronchoscopy | B | |
| Palliation in DNR/DNI patients | B | |
| Postextubation respiratory failure | B | |
| Weak | ALI/ARDS | C |
| Neuromuscular disease | C | |
| Pneumonia | C | |
| Status asthmaticus | C |
∗ Strength of recommendation: strong, recommended therapy; intermediate, strongly consider in good candidates for NIV; weak, cautious trial can be performed in otherwise excellent candidates for NIV.
† Quality of evidence: A, multiple randomized controlled trials showing benefit with NIV; B, single randomized trial or nonrandomized trials showing benefit with NIV; C, conflicting evidence or evidence of harm with NIV.
First-Line Therapy
COPD Exacerbations
Multiple randomized, trials meta-analyses, and, more recently, comparative effectiveness analyses have shown decreased intubation and improved mortality rates with NIV use compared with standard medical therapy in patients with exacerbations of COPD. Therefore NIV should be considered the standard of care in patients with COPD exacerbations requiring ventilatory support in the absence of contraindications. The physiologic rationale in these patients is that NIV unloads the inspiratory muscles and increases tidal volume, decreases the dead space-to-tidal volume ratio, lowers respiratory rate, and improves alveolar ventilation. The addition of positive end-expiratory pressure (PEEP) decreases the work of breathing by decreasing the inspiratory threshold load imposed by auto-PEEP that is frequently present in these patients.
Acute Cardiogenic Pulmonary Edema
Multiple randomized trials and meta-analyses have shown that either continuous positive airway pressure (CPAP) alone or NIV lowers intubation rates and mortality when compared with conventional medical therapy in patients with cardiogenic pulmonary edema. The benefit in these patients primarily reflects an increase in intrathoracic pressure. Higher intrathoracic pressure increases functional residual capacity (FRC), recruiting flooded alveoli, improving gas exchange, and improving lung compliance. An increase in intrathoracic pressure also reduces cardiac preload and afterload, improving hemodynamics in most patients with cardiogenic pulmonary edema. Longer term use of CPAP in stable congestive heart failure patients improved left ventricular ejection fraction, decreased mitral regurgitation, and decreased atrial natriuretic peptide levels compared with controls. Whether CPAP alone or NIV (i.e., pressure support plus PEEP) is the preferred modality is unclear. An early study showed an increased rate of myocardial infarctions with NIV, but subsequent trials and meta-analyses have failed to replicate this and have instead demonstrated that both modalities similarly reduce the need for intubation and lower mortality rates. Although CPAP has been suggested as the preferred initial modality because of its greater simplicity and lower expense, most centers initially use NIV because bilevel devices are readily available and unloading of the inspiratory muscles may be achieved more quickly. In unstable patients with pulmonary edema complicating ST-elevation myocardial infarction, or in the presence of cardiogenic shock, early intubation is recommended.
Immunocompromised States
NIV decreases mortality compared with oxygen therapy alone in immunocompromised patients with hypoxemic respiratory failure. This includes patients with hematologic malignancies, patients who have had solid organ transplantation, or patients with HIV or AIDS. The beneficial effects are attributed to the avoidance of infectious complications related to intubation. These patients are particularly vulnerable to intubation-associated pneumonias and septic complications. We would recommend instituting this therapy early when there is a window of opportunity to avoid the progression to overt respiratory failure and the need for intubation. Once intubated, mortality rates among the immunocompromised may be very high, although they appear to be declining. In a retrospective observational study of patients with malignancy (including hematologic malignancies) and ARDS, mortality rates improved over time (89% in the first 5 years compared with 52% over the last 5 years). However, there was continued evidence of high mortality (68.5%) in patients with severe ARDS (partial pressure of arterial oxygen (Pao 2 )/fraction of inspired oxygen (Fio 2 ) ≤ 100). Higher rates of NIV failure were observed in patients with moderate or severe ARDS and in patients experiencing NIV failure.
Extubating Patients with COPD
Studies have shown decreased duration of mechanical ventilation and improved mortality when intubated COPD patients who have failed spontaneous breathing trials are extubated and supported with NIV. However, this approach should be used with extreme caution. Patients should be excellent candidates for NIV in every other way—hemodynamically stable, cooperative, having a good cough and manageable secretions, and able to be ventilated with pressure support levels not exceeding 15 cm H 2 O. Furthermore, initial intubation should not have been technically difficult because of the potential for catastrophe should these patients require emergent reintubation. The authors have found early extubation to NIV to be useful in avoiding the need for tracheostomies in such patients. However, if this approach fails and reintubation is necessary, we usually proceed to prompt placement of a surgical airway.
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