Introduction
Mechanical ventilation (MV) is a life-saving procedure with applications in acute and chronic respiratory failure. Since the late 1950s, mechanical ventilation has been preferentially delivered by direct access to the lower airways through an endotracheal tube, such as during general anesthesia and surgery, or via a tracheostomy cannula.
Since the late 1980s, home MV has been increasingly applied in patients with chronic restrictive or obstructive respiratory disorders via noninvasive techniques, with the main objective of improving patients’ quality of life compared with home tracheostomy. Manufacturers have devoted considerable technologic effort to develop specific home ventilators for “leaky” ventilation and to provide comfortable and adaptable interfaces. The recognition that major sleep disturbances could be caused by abnormal respiration has also contributed to the widespread use of different kinds of home ventilatory support. Noninvasive ventilation (NIV) is therefore the standard of care for home mechanical ventilation.
In the early 1990s in parallel with the expansion of home NIV, clinicians started to demonstrate a major interest in this technique as a way of avoiding endotracheal intubation in the acute care setting. The indications have progressively been extended from acute hypercapnic respiratory failure to a large variety of clinical situations with different degrees of respiratory failure significantly expanding the number of patients currently treated with NIV. In the acute care field, technical improvements and specific equipment came late and benefited from improvements made for home ventilation. Currently, there are a number of specific indications for the use of NIV as the standard of care for acute respiratory failure. However, there are also many situations where there is uncertainty about the usefulness or the limits of this technique, explaining large variations in its use internationally ( Table 102-1 ).
| DISEASE | Clinical Status | ||||
|---|---|---|---|---|---|
| Recommended | Intermediate Recommendation | Weak Recommendation | No, or Contraindication | Yes | No |
| Exacerbations of COPD Acute cardiogenic pulmonary edema Acute respiratory failure in immunocompromised patients Facilitation of weaning/extubation in patients with COPD Postoperative hypoxemia after major abdominal or lung surgery Acute respiratory failure in patients with obesity-hypoventilation Do-not-intubate patients | Asthma Hypoxemic respiratory failure in nonimmunocompromised patients Preventive use during procedures (upper endoscopies, endotracheal intubation)Community-acquired pneumonia in patients with COPD Extubation failure in patients with COPD Postoperative preventive (cardiac, upper abdominal-bariatric surgery) Neuromuscular disease | Mild-moderate ARDS Community-acquired pneumonia (non-COPD) TraumaExtubation failure (non-COPD) Postoperative preventive following esophageal or lung surgery (using low pressures) | Severe ARDS ARDS with multiple organ dysfunction End-stage interstitial pulmonary fibrosis Facial trauma Facilitation of weaning (non-COPD) Undrained pneumothorax Upper gastrointestinal bleeding | Conscious and cooperative (except encephalopathy in COPD) Hypercapnic failure Hemodynamically stable No multiple organ failures Improvement in gas exchange, respiratory, and heart rate within first 2 hr | Hemodynamic instability Loss of consciousness, drowsiness Abdominal distention, nausea or vomiting Uncooperative patient Inexperienced staff Upper airway obstruction |
Soon after the introduction of invasive MV via a tube in the trachea, many complications of positive pressure ventilation were identified. These complications generated concern about the invasiveness of MV. The endotracheal intubation procedure and the tube itself have been implicated in a large number of complications. Some are directly related to the intubation procedure, such as cardiac arrest following endotracheal intubation, and laryngeal or tracheal injury leading to long-term sequelae. Others are related to the fact that the endotracheal tube bypasses the barrier of the upper airway, setting the stage for ventilator-associated pneumonia that carries its own risk of morbidity and mortality. Mechanical ventilation often requires sedation, which itself is often a cause of prolonged weaning and prolonged mechanical ventilation. These major safety considerations prompted the development of noninvasive methods for delivering positive pressure ventilation. Thus, in patients with acute respiratory failure, the main goal of NIV has been—and still is—to provide ventilatory assistance while lowering the risk of adverse events by reducing the need for invasive MV. Convincing evidence that NIV diminishes the risk of infectious complications has been obtained from randomized controlled trials and meta-analyses, as well as from large cohort studies and case-control studies, which have demonstrated substantial decreases in all categories of nosocomial infection. The reason is that NIV is in general associated with a reduction in the overall invasiveness of patient management: Sedation is usually not required or, if necessary, it is administered at low doses, and the use of central venous lines, urinary catheters, and other invasive devices is reduced compared with patients receiving endotracheal MV ( Fig. 102-1 ).
Another important factor favoring the use of NIV is the growing number of patients who are unwilling to accept endotracheal intubation (ETI) or are considered poor candidates for endotracheal MV because of a fragile underlying health status. In these patients, NIV offers a chance of recovery with a low risk of complications and can be considered as a ceiling of therapy with acceptable risks. By postponing ETI, NIV may also provide a window of opportunity for the physician, family, and patient to make informed decisions about the goals of therapy in patients treated with palliative care. Potential benefits and risks of the technique are discussed later and summarized in Table 102-2 .
| Benefits | Risks |
|---|---|
| Unload the respiratory muscles Improve gas exchange Decrease left ventricular afterload (in non-preload-dependent patients) Decrease right and left ventricular preload Reduce the invasiveness of patient management Decrease ICU and hospital stay Diminish the risk of nosocomial infections Decrease complications Decrease mortality | Intolerance related to interface Abdominal distention and regurgitation Skin lesions Masking deterioration of underlying disease Frequent unrecognized patient-ventilator asynchrony May promote large tidal volumes and high transpulmonary pressure swings (potential for VILI) |
Pathophysiology, Rationale, and Expected Benefits
Chronic Obstructive Pulmonary Disease Exacerbation
Exacerbation of chronic obstructive pulmonary disease (COPD) is a common cause of admission to the hospital and intensive care unit (ICU). Worsening of dyspnea and symptoms of acute bronchitis are accompanied by rapid and shallow breathing leading to hypoxemia and hypercapnia. Right ventricular failure, encephalopathy, and cardiorespiratory arrest can ensue. The main pathophysiologic pathway comes from an inability to maintain adequate alveolar ventilation in the presence of major abnormalities in respiratory mechanics. The transdiaphragmatic pressure generated by these patients can be considerably higher than normal and represents a high percentage of their maximal diaphragmatic force, a situation that carries a risk of respiratory muscle fatigue. These changes are accompanied by a high respiratory drive, due to strong stimulation of the respiratory centers by acidosis and hypoxemia. This vicious circle can be modified by NIV, which allows the patient to take larger tidal volumes with less effort, thus reversing the clinical abnormalities resulting from hypoxemia, hypercapnia, and acidosis. The main role of NIV is to allow the patient to increase tidal volume at a lower level of energy expenditure. Ventilatory support working in synchrony with the patient’s efforts allows larger breaths to be taken with less effort. As a result of increased alveolar ventilation, arterial partial carbon dioxide pressure (arterial P co 2 ) and pH values improve and this, in turn, reduces the patient’s ventilatory drive, thereby lowering the respiratory rate and improving dyspnea.
Cardiogenic Pulmonary Edema
In cardiogenic pulmonary edema (CPE), breathing becomes difficult because pulmonary congestion reduces lung compliance, causes hypoxemia and increases the work of breathing. Most patients with CPE improve rapidly with medical therapy. A few, however, develop severe respiratory distress and/or refractory hypoxemia/hypercapnia and require ventilatory support until the medical treatment starts to work. This is particularly common in elderly patients, who may also have a mild degree of chronic bronchitis. Several NIV modalities have been used successfully, with the main goal of preventing the need for ETI and/or hastening the improvement provided by medical therapy. The negative swings in intrathoracic pressure increase venous return, while at the same time the negative intrathoracic pressure can impede left ventricular ejection. Respiratory distress and hypercapnia develops, especially if underlying pulmonary abnormalities are present. Continuous positive airway pressure (CPAP) and other types of NIV can elevate intrathoracic pressure and reduce the negative pleural swings, decrease shunt, and improve arterial oxygenation and dyspnea in patients with CPE. Interestingly, NIV can substantially lessen the work of breathing and, at the same time, improve cardiovascular function by decreasing left ventricular afterload in non–preload-dependent patients and reduce right and left ventricular preload. In one trial, high-dose nitrate bolus therapy was far more effective clinically than NIV with a low dose of nitrates. It is important to stress the vulnerability of patients with CPE, particularly those with coronary heart disease, and to emphasize that NIV cannot replace adequate medical therapy.
Hypoxemic Acute Respiratory Failure
Unlike exacerbations of COPD or even CPE, hypoxemic acute respiratory failure (ARF) represents a heterogeneous group of diseases with different prognoses and treatments. The main common characteristic is hypoxemia, and it is frequently not associated with frank ventilatory failure, at least in the initial phase. Robust large randomized controlled trials are relatively scarce in this setting, and guidelines and recommendations are often not straightforward. The heterogeneity of these patients explains some of the contradictory results in the literature, suggesting that the outcome may vary with the study population. The various subgroups of hypoxemic ARF may thus need to be examined separately.
The hallmark of hypoxemic ARF is acute hypoxemia (arterial P o 2 /F io 2 ratio ≤ 300) that necessitates high levels of oxygen and is accompanied by clinical signs of respiratory distress reflecting a high respiratory drive often causing hyperventilation and hypocapnia. The development of hypercapnia is considered a serious late complication, generally indicating impending respiratory muscle fatigue. The rationale for using NIV in hypoxemic ARF is to alleviate the high load imposed on the respiratory muscles (prevention of latent pump failure) and to “treat” hypoxemia (lung failure). Two specific issues regarding the use of NIV for this indication should therefore be mentioned: (1) NIV is not a cure for the disease and, when interrupted or poorly delivered, the patient immediately returns to the pre-NIV state. In fact, a beneficial effect of NIV on gas exchange and dyspnea may mask disease deterioration. This could lead to life-threatening respiratory failure in case NIV is subsequently interrupted. (2) During the initial phase, patients sometimes are able to cope with the workload imposed on the respiratory muscles with no apparent need for ventilatory support. However, by the time they become completely unable to meet the respiratory requirements, NIV use may be ineffective or even harmful. Therefore there is probably a time and/or a severity window for delivering NIV as a preventive support beyond which its use may become risky ( Fig. 102-2 ).
Moreover, many patients with acute respiratory distress syndrome (ARDS) may not be favorable candidates for NIV due to the need for delivering lung protective ventilation. During NIV, high transpulmonary pressure swings and large tidal volumes may be generated, which could lead to the development of ventilator-induced lung injury (VILI) and contribute to the poor outcome observed in intubated patients who fail NIV. Most patients with hypoxemic ARF have a high respiratory drive, and it has been shown experimentally that the increased drive caused by a severe metabolic acidosis may cause lung injury.
In clinical practice, the total pressure delivered during NIV is limited by the leaks that result from high pressures in the mask. To determine the effects of different combinations of pressure support and positive end-expiratory pressure (PEEP), the work of breathing and gas exchange was measured in patients with acute lung injury receiving NIV for ARF. The highest level of PEEP studied (10 cm H 2 O) resulted in the greatest oxygenation improvement, but CPAP alone failed to unload the respiratory muscles. Decrease in the work of breathing and dyspnea necessitated the provision of pressure support. To handle the lung and pump failure with NIV, clinicians should provide a sufficient level of PEEP to improve oxygenation, while ensuring an optimal pressure support to unload the respiratory muscles. These two additive but sometimes conflicting pressures generate the peak airway pressure, one of the major determinants of leaks and asynchrony. Patients with poor respiratory mechanics requiring high airway pressures may thus prove difficult to manage with NIV.
Practical and Technical Aspects
Modes of Ventilation and Settings
Continuous Positive Airway Pressure and Pressure-Support Ventilation
Continuous positive airway pressure (CPAP) represents the application of a constant level of positive pressure at the airway opening during spontaneous breathing and is widely used in the ICU, particularly in neonates and infants in whom it was first applied. Positive pressure applied at the mouth was shown as early as the 1930s to improve dyspnea in CPE. CPAP is not always considered to be a true mode of ventilatory support, but it often provides ventilatory assistance in terms of a patient’s work of breathing and oxygenation and achieves the usual goals of ventilatory support. Although there is some debate in the literature, in this chapter, CPAP is considered as a type of NIV. An advantage of CPAP over more complex modes of mechanical ventilatory assistance is that CPAP does not require patient-ventilator synchronization. CPAP results in a higher mean intrathoracic pressure than unassisted spontaneous breathing, with beneficial effects on atelectasis and improvement in oxygenation. Lung compliance can increase, reducing work of breathing, and the presence of intrinsic PEEP (PEEPi) can be counterbalanced with a partial reduction of inspiratory effort.
In patients without COPD, CPAP can increase functional residual capacity and may displace ventilation up from the lower flat portion of the respiratory system volume-pressure curve to a more linear portion. Through this mechanism, CPAP can improve oxygenation and respiratory mechanics and potentially reduce the work of breathing. L’Her and colleagues could not find any significant effect of CPAP on respiratory effort in patients with acute lung injury, in contrast with marked reduction under pressure-support ventilation (PSV). Delclaux and colleagues evaluated whether CPAP, compared with conventional medical treatment and oxygen alone, reduced the need for ETI in normocapnic patients with acute lung injury. Despite a favorable early physiologic response to CPAP in terms of oxygenation, no outcome benefits were observed. This failure of noninvasive CPAP to provide clinical benefits may be due to the absence of any effect on respiratory effort.
This differs from the results of studies in CPE, in which PSV was comparable or only slightly superior to CPAP alone in terms of the decrease in respiratory effort. In patients with CPE, CPAP raises intrathoracic pressure, improves oxygenation and dyspnea, and lessens the work of breathing. In addition, an increase of intrathoracic pressure decreases transmural pressure of the left ventricle and of the thoracic aorta, reducing left ventricular afterload. Chadda and colleagues found that CPAP and PSV resulted in similar cardiac and hemodynamic effects, by producing similar reductions in right and left ventricular preload mediated by similar effects on intrathoracic pressure.
One early clinical trial found more ischemic cardiac events using pressure support than using CPAP, but it was difficult in this small study to differentiate randomization imbalance from true physiologic effects. Although these effects were not confirmed in later studies, it raised doubts on its use in patients with ischemic cardiac diseases.
Pressure support is the most frequently used ventilatory mode during NIV. In patients with severe hypoxemia, ventilatory support should be able to relieve the dyspnea, improve oxygenation, and decrease the patient’s effort to breathe. Combined PEEP and pressure support are needed to achieve these goals. As discussed earlier, the compromise between setting PEEP and pressure support during NIV use may be challenging. The total pressure delivered by the ventilator is often reduced to avoid inducing excessive leakage that would complicate NIV administration and impair patient-ventilator synchrony; however, insufficient pressure may translate into unsatisfactory inspiratory muscle unloading.
Asynchronies During Noninvasive Pressure-Support Ventilation
Success of NIV is strongly associated with good clinical tolerance : Problems of intolerance can be related to the patient, interface, ventilator, and/or ventilator settings. A specific problem during NIV is the presence of leaks around the mask, which may lead to discomfort and patient-ventilator asynchrony, thereby further worsening the clinical situation. Patient-ventilator asynchrony is defined as a mismatch between the patient’s neural inspiratory time and the ventilator insufflation time. Two types of asynchrony can be directly caused by leaks during NIV with pressure support: prolonged inspiration due to inspiratory leaks and auto-triggering due to expiratory leaks. An optimal adjustment of ventilatory settings may improve patient-ventilator synchrony, work of breathing, comfort, and, potentially, the success of NIV.
An observational study used surface diaphragmatic electromyographic activity to evaluate the incidence of patient-ventilator asynchrony in 60 patients during 30-minute sessions of NIV. Frequent asynchronies accounting for more than 10% of the respiratory efforts were present in 43% of the patients. Most of these patients were ventilated with an ICU ventilator with no specific “NIV function” activated, which probably contributed to this high incidence. Prolonged insufflation due to delayed cycling was the most frequent asynchrony, seen in about 25% of the patients. When large leaks develop during inspiration, the ventilator continues to deliver pressure because the delivered flow remains above the cycling criterion (also referred to as expiratory trigger value ), so the cycle does not turn off until a time limit is reached. In this situation, the patient attempts to exhale and can fight against the ventilator because the expiratory valve remains closed, generating ineffective efforts during persistent insufflation. The magnitude of delayed cycling and the number of ineffective breaths are directly associated to the magnitude of leaks. This problem is much more prevalent when using an ICU ventilator with no “NIV” mode but may arise also with NIV-dedicated ventilators. Limiting the total inspiratory pressure by reducing the pressure support and/or the PEEP level may be helpful. Persistent leaks indicate a need for limiting the ventilator insufflation time by increasing the expiratory trigger and/or reducing the maximal inspiratory time. Most of the new-generation intensive-care ventilators and many NIV-dedicated ventilators allow adjustment of the expiratory trigger or maximal inspiratory time.
Expiratory leaks can also generate a pressure drop below the external PEEP level or a drop in expired bias flow, simulating the patient’s effort and triggering a ventilator breath. Auto-triggering may promote a short cycle or a flow distortion because the patient does not generate any effort and “fights” the ventilator. NIV-dedicated ventilators have specially designed algorithms that markedly limit auto-triggering.
Other Modalities
Volume-Targeted Ventilation.
Volume-targeted ventilation delivers set flow, inspiratory time, and tidal volume with each breath; inflation pressure varies with the intensity of the patient’s effort. Volume-targeted ventilation is rarely used in ARF because it may induce high peak mask pressures, causing discomfort and leaks, risk of gastric distension, pressure sores, and skin necrosis. Controlled modes may, however, be preferred in patients with apnea and hypopnea or unstable ventilatory drive (pressure- or volume-targeted modes), and volume-targeted modes will be preferred in case of unstable respiratory mechanics or failure of pressure-targeted modes to augment spontaneous breathing.
Negative pressure ventilation is available in a few centers in the world. In acute exacerbations of COPD, it seems to provide better outcomes than conventional invasive MV and may be similar to face mask NIV. The use of a helium-oxygen mixture (heliox) for NIV has received much interest because its decreased density leads to decreased resistance in regions with turbulent flow. There were some early promising results in patients with COPD exacerbations. Unfortunately, large clinical trials were unable to demonstrate a significant clinical benefit when heliox was compared with a conventional gas mixture during NIV. One possible reason for these negative results is that the rate of NIV failure has progressively declined in the groups treated with standard air-oxygen mixtures, making it more difficult to demonstrate a difference in favor of heliox.
Proportional assist ventilation (PAV) is a physiologically sound mode designed to deliver ventilatory support in response to the patient’s needs. Several studies have compared PAV to PSV during NIV, and the efficacy of the two techniques appears similar. The largest prospective randomized trial, by Fernandez-Vivas and associates, was performed in 117 patients with mixed causes of ARF and showed no difference in clinical outcomes between NIV delivered with PSV or proportional-assist ventilation. PAV was more comfortable, and intolerance was less common. Noninvasive estimation of resistance and elastance are needed for PAV, and leaks make the settings of this mode particularly difficult during NIV.
Neurally adjusted ventilatory assist (NAVA) is based on the detection and quantification of the electrical activity of the diaphragm (EAdi) by means of an esophageal array of bipolar electrodes. NAVA uses the EAdi to control not only the timing but also the amount of pressure delivered. The ventilator is triggered, limited, and cycled-off directly by EAdi. Neural control of mechanical ventilation has the capability of enhancing the synchrony between mechanical ventilation and respiratory muscle activity, hence improving patient comfort. Another advantage is that NAVA should not be affected by leaks. Recently, Beck and colleagues showed, in rabbits, that NAVA can deliver assist that is in synchrony and proportional to EAdi even when a “leaky” noninvasive interface was used. It has also been tested with a helmet, which covers the entire head, in hypoxemic patients after extubation. In 10 hypoxemic patients after extubation, Cammarota and colleagues found that NAVA delivered by helmet improved patient-ventilator interaction and synchrony compared with pressure support ventilation. More work needs to be done to determine whether NAVA can maintain adequate levels of ventilator assistance and ensure harmonious patient ventilator interaction in different kinds of respiratory failure.
Ventilators
CPAP Systems
Many systems can be used to deliver CPAP. One of the most frequently used consists of a high-flow generator producing an air/oxygen mixture based on the Venturi effect, with an additional source of oxygen and a mechanical expiratory valve. An inspiratory reservoir and a CPAP water valve or a standard mechanical ICU ventilator in CPAP mode can also be used. The Boussignac CPAP device is a small cylindrical plastic adaptor that fits onto a modified face mask. The system uses the incoming flow of oxygen to generate a turbulent virtual pressure valve in the open expiratory side of the mask. The gas is accelerated and circumferentially enters into the open-ended cylinder, generating air entrainment and positive pressure.
ICU or Specific NIV Ventilators
Because ICU ventilators can become less efficient in the presence of leaks, most manufacturers have developed a specifically designed “NIV mode.” This mode detects leaks and automatically adjusts the inspiratory trigger to avoid auto-triggering and the expiratory cycling criterion to avoid prolonged inspiration. These new NIV modes reduce several of the asynchronies observed during NIV. NIV can be delivered using ICU ventilators or ventilators specifically dedicated for NIV. In a survey from North America of NIV use, these NIV-dedicated ventilators were the most frequently used ventilators, accounting for two thirds of cases, whereas CPAP generators represented around 30% and ICU ventilators less than 5%. By contrast, a survey in French ICUs found that an ICU ventilator was used in almost 80% of the cases and NIV and home ventilators represented less than 20% of the cases.
NIV ventilators perform well in the presence of leaks, but important differences exist among NIV ventilators. The advantages of ICU ventilators are better monitoring capabilities and the ability to continue invasive mechanical ventilation and full ventilatory support in the event of ETI. No outcome data, such as NIV success or failure, have been shown to be associated with specific asynchronies but, if an ICU ventilator is used, it seems reasonable to use the dedicated NIV algorithm. Adequate patient monitoring may be essential to assess patient-ventilator interaction, detect leaks, and fine-tune pressure levels. A randomized clinical study showed that careful observation of the airway pressure and flow-time curves on the ventilator screen can detect patient-ventilator asynchronies and accelerate arterial P co 2 normalization and patient adaptation. Whether this also ensures higher NIV success rates remains to be determined.
Airway gas conditioning (i.e., the warming and humidification of the inspired gas) constitutes a physiologic procedure performed by the human airway during normal breathing. When the upper airway is bypassed, as during invasive MV, it is necessary to heat and humidify the gas before delivery. During NIV, gas is transferred to the alveoli through the mouth and nose, but the normal airway gas conditioning mechanisms can be insufficient when there are high-flow, high-airway pressure settings and high inspired oxygen fractions. Artificial heating and humidification are usually necessary because inadequate humidification during NIV can cause damage to the nasal mucosa, induction of high nasal airway and possible difficulty with intubation in cases of NIV failure. ICU ventilators provide much lower levels of humidity compared with turbine or piston NIV ventilators due to the exclusive use of dry gases, and with ICU ventilators, gas humidification is mandatory. Two types of humidification systems can be used: heated humidifiers or heated and moisture exchanger filters. Firm recommendations cannot be made between the two systems—the humidification ability of moisture exchanger filters is reduced in the presence of leaks, and their internal volume may impose an additional workload by generating carbon dioxide rebreathing. In patients with hypercapnic respiratory failure, this can diminish the ability of NIV to reduce blood carbon dioxide levels and correct respiratory acidosis. Leaks, however, may reduce the impact of this problem by removing carbon dioxide-rich gas from the mask. A randomized trial did not find any difference in the rate of NIV failure using a moisture exchanger filter or a heated humidifier on ICU ventilators. A similar problem of carbon dioxide rebreathing may arise when ventilators (using ambient room air), equipped with a one-line circuit, are used with the minimal level of PEEP allowed on these ventilators.
Interfaces
The interface is an essential component that differentiates NIV from invasive MV. The interface used to connect the patient to the ventilator is usually a full face mask covering both the nose and the mouth. An important distinction concerns leaky masks for single-circuit ventilators versus masks without intentional leaks for double-circuit or for a single circuit equipped with an expiratory valve. New masks are often made of two or more parts hooked or glued together: a frame made of stiff transparent material and a cushion of soft material to seal the frame against patient face. Improvements have been realized by using different cushions with new materials (such as hydrogel), by improving the fixation system with particular attention to skin and eye care, and by increasing the number of the attachment points permitting a more uniform distribution of pressure.
Masks can be used for the nose or the mouth. Nasal interfaces are available, but their use in ICU patients frequently results in major leakage through the mouth that diminishes the effectiveness of NIV and promotes asynchrony and discomfort. There are two existing types of nasal interfaces: nasal masks, designed to cover either the full nose or the nares only, and nasal “pillows” directly inserted into the nostril. Like oral interfaces, the nasal interfaces are mostly used for chronic NIV. The use of a nasal mask in the ICU leads to mask failure in more than 70% of the patients. Oral interfaces are associated with significantly more leaks and asynchrony and require better patient cooperation.
Full face masks could be either oronasal or total face; both appear to have similar efficacy and patient tolerance. Large masks enclosing the entire face or head have been developed. Interestingly, clinical physiologic studies comparing these large masks to standard full face masks have shown comparable efficacy in terms of respiratory muscle unloading, suggesting that the theoretical risk of rebreathing associated with the large internal volume may be small or nonexistent in clinical practice. Fraticelli and colleagues studied the effect of four interfaces—a mouthpiece, a facial mask, and two oronasal interfaces (with small and large internal volume)—on minute ventilation, gas exchange, and work of breathing of patients with acute respiratory failure. Despite large variations in the internal volume of the devices, the authors found no difference in patients’ respiratory effort, arterial blood gases, and breathing pattern.
Helmets, which cover the entire head, have been tested. Use of a helmet was originally proposed for CPAP primarily for patients with acute hypoxemic respiratory failure ; a specifically designed helmet has also been used for NIV. Helmets may induce more rebreathing than other masks and may be less suitable for patients with hypercapnic respiratory failure. The helmet requires higher pressures than conventional masks to produce the same efficacy. Rebreathing with the helmet, compared with other NIV interfaces (two oronasal masks, a total face mask) was studied by Fodil and coauthors ; in this in vitro study, the authors showed a large difference between the internal volume of mask (which is about 10 L for the helmet) and the dynamic effective dead space, which can be much smaller due to the streaming effect of gases.
The oronasal mask appears to be the best first choice interface. The nasal mask may be comfortable, but because some patients breathe largely through their mouths, outcomes for patients with respiratory distress are usually less favorable. The total/full-face mask has not demonstrated a clear superiority to the oronasal mask in terms of clinical effectiveness and tolerability but is a possible alternative. The helmet can be used as a first-line interface in experienced hands and for some indications such as pulmonary edema. There is no ideal NIV interface for all patients in all circumstances, and several interfaces should be available at the bedside. With few exceptions (such as the nasal mask and the mouthpiece), interfaces are largely interchangeable in the acute care setting.
Indications
Exacerbation of Chronic Obstructive Pulmonary Disease
An international consensus conference published in 2001 recommended that NIV should be considered as the first-line treatment in patients with COPD exacerbations; more recently, different national guidelines advocated this practice. A Cochrane database review demonstrated that, in these patients, NIV use was associated with decrease in mortality, reduced need for intubation, less treatment failure, faster clinical improvement, and a reduction in treatment complications and length of hospital stay. The Global Initiative for Chronic Obstructive Lung Disease in 2013 reinforced the importance of NIV when treating COPD exacerbations based on the high success rate (80% to 85%).
The first evidence that NIV markedly reduced the need for ETI came from a case-control series reported in 1990. Subsequently, several prospective randomized trials confirmed that NIV reduced the need for ETI and the rate of complications, shortened the length of stay, and improved survival in patients with COPD. Studies conducted in the United Kingdom established that NIV was also effective in non-ICU settings. In the largest ICU study, Brochard and colleagues randomized 85 patients with COPD to treatment with or without face mask PSV. The ETI rate was 74% in the group that received standard medical treatment and 26% in the NIV group. Benefits in the NIV group included a decreased rate of complications during the ICU stay, a shorter length of hospital stay, and, more importantly, a significant reduction in mortality (from 29% to 9%). The overall decrease in mortality was due to reductions in the need for ETI and in various ICU-related complications.
Plant and colleagues conducted a prospective multicenter randomized trial comparing standard therapy alone (control group) to NIV in 236 COPD patients admitted to general respiratory wards for ARF. Treatment failure (defined as fulfillment of criteria for ARF) was more common in the control group (27%) than in the NIV group (15%), and NIV was associated with a lower in-hospital mortality rate. These studies made clear that early NIV should be an important component of first-line therapy of COPD exacerbations to prevent further deterioration.
A recent study used a large database and analyzed more than 7 million admissions for acute exacerbations of COPD in the United States from 1998 to 2008, of which 612,650 (8.1%) required respiratory support. The authors showed an increase in the use of NIV (from 1% to 4.5% of all admissions) and a 42% decline in invasive MV (from 6% to 3.5% of all admissions). Intubation and in-hospital mortality declined during this period. By 2008, NIV was used more frequently than invasive MV as the first-line therapy for acute exacerbations of COPD.
A learning curve exists for NIV. In a single-center study by Carlucci and colleagues, the NIV success rate remained stable over the study period but patients treated with NIV during the last few years of the study period had more severe disease, higher arterial P co 2 levels, and lower pH values. This indirectly reflected that more severe exacerbations could be treated with NIV out of the ICU over the years. In an 8-year study performed in a French university referral hospital, NIV use increased gradually, in step with a decline in conventional treatment with ETI. In parallel, the nosocomial infection and mortality rates significantly diminished.
NIV for patients with COPD exacerbations can be administered by experienced staff outside the ICU, but it is recommended that the most severely affected patients, such as those with an arterial pH less than 7.30 on admission, should be managed in the ICU. A low pH, marked mental status alterations at NIV initiation, presence of comorbidities, and a high severity score are associated with a higher rate of early NIV failure. A few patients experience late or secondary failure after an initial improvement. In a recent observational prospective study, the presence of pneumonia and the serum albumin as an indicator of patient’s nutritional status were identified as the most important determinants of NIV outcome in COPD patients. These patients with late NIV failure (need for intubation after 72 hours or persistent dependence on NIV) may have more severe disease and exhibit sleep deprivation. A longer time from onset of the COPD exacerbation to NIV initiation may also reduce the likelihood of success. Every effort should be made to deliver NIV early, and close monitoring is necessary when NIV is initiated at a late phase, a situation where its use is less effective. Several observational studies and one small randomized trial showed positive clinical results in patients with hypercapnic encephalopathy due to COPD exacerbation and suggested that even at this stage it may be worth trying to “wake up” the patient with NIV.
A few studies have suggested that NIV use may be associated with higher 1-year survival rates, as compared with standard ICU therapy or invasive MV. These studies have a number of methodologic flaws, but the consistency of the results suggests interesting long-term benefits of NIV. Some authors argue for continuing NIV at home after exacerbations. One of the benefits could be a reduction of the readmission rate, as suggested in one small randomized controlled trial.
In conclusion, NIV offers many advantages over standard medical therapy and invasive MV to treat exacerbations of COPD and there is strong evidence that NIV is cost effective, being both more efficient and cheaper compared with standard therapy alone.
Asthma
NIV can be used in asthmatic patients not responding well to medical treatment, and there is a growing interest in this technique and its combination with aerosol therapy. A recent report using a large U.S. database indicated that there has been a substantial increase in the use of mechanical ventilation for acute asthma over the past years, accompanied by a shift from invasive mechanical ventilation to NIV. Only a few small randomized trials have rigorously evaluated the benefits. Two cohort studies found beneficial short-term effects of NIV in asthmatic patients whose condition was deteriorating despite medical therapy. In a randomized trial, all patients treated for acute asthma were randomized to either NIV with two different levels of pressure support and PEEP or to oxygen. A greater reduction in dyspnea was observed in the NIV groups compared with the control group. The NIV group with the higher pressure demonstrated a significant improvement in the forced expired volume in 1 second compared with the control group. Two other trials found faster improvement in lung function using NIV with a shorter length of stay or a reduced need for hospitalization.
Exacerbation of Other Chronic Lung Diseases
All forms of acute-on-chronic ventilatory failure share several common pathophysiologic pathways. NIV seems to be an interesting option in patients with restrictive lung disease, especially when respiratory system compliance is still preserved. A recent large cohort study compared the efficacy of NIV in patients with COPD ( n = 543) and in patients with acute respiratory failure due to obesity hypoventilation syndrome ( n = 173). Patients with obesity hypoventilation had fewer late NIV failures, but overall survival adjusted for confounders, length of stay, and hospital readmission were similar in both groups. In patients with COPD, obesity was associated with less late NIV failure and hospital readmission. These data strongly argue for the fact that patients with obesity hypoventilation syndrome can be treated with NIV during an episode of acute exacerbation with similar efficacy and better outcomes than patients with COPD.
Cardiogenic Pulmonary Edema
Clinical Results
The first evidence of therapeutic efficacy of positive pressure use during acute CPE was shown in 1985. Rasanen and colleagues randomized 40 patients with acute CPE and respiratory failure to conventional therapy or face mask CPAP of 10 cm H 2 O. The interventional group demonstrated better improvement of gas exchange, a decrease of respiratory work, and a tendency to a lower intubation rate. Subsequently, other randomized trials conducted in the emergency department or in the ICU comparing CPAP with pressure support plus PEEP (PSV plus PEEP) with standard therapy found that the two techniques improved arterial blood gases and respiratory rate and significantly reduced the rate of ETI.
Recently published guidelines recommend NIV use in patients with acute CPE, dyspnea, and respiratory rate greater than 20 breaths/min to improve clinical symptoms. Nevertheless, intubation is often the best option in patients with cardiogenic shock and low blood pressure (systolic blood pressure < 85 mm Hg) or altered level of consciousness. In more recent European guidelines, the level of evidence (level B-class IIa) for NIV use to treat acute CPE was lower than that formerly recommended. This decrease in the level of recommendation was mainly due to the publication of the 3CPO trial, the largest multicenter controlled study to date. It was performed in the emergency department and evaluated the possible benefits of NIV in acute CPE. Patients admitted with a clinical and radiologic diagnosis of acute CPE, respiratory rate greater than 20 breaths/min and pH less than 7.35 were randomized to conventional pharmacologic therapy plus NIV (CPAP or PSV plus PEEP) or standard oxygen therapy. The study included 1069 patients and showed that NIV was associated with faster reduction in dyspnea, heart rate, and earlier resolution of metabolic abnormalities than standard oxygen therapy. Intubation rates were low and not different between groups (3%), and 7- and 30-day mortality rates (9.8% vs. 9.5% and 16.4% vs. 15.2%) were similar in the control and NIV groups, respectively. The control group was characterized by a high incidence of crossover (15%) to PSV plus PEEP or CPAP. Without this crossover, a much higher rate of intubation might have been observed in the oxygen group. Other study limitations were (1) severely ill patients, who required “lifesaving or emergency intervention,” were excluded and might have benefited from NIV; (2) patients had mild hypoxemia; and (3) a low intubation rate was observed.
A more recent multicenter clinical trial of 207 patients with acute CPE compared oxygen therapy at 15 L/min to 7.5 to 10 cm H 2 O CPAP initiated outside the hospital and continued in-hospital in the ICU. The CPAP intervention group demonstrated a significantly greater and faster resolution of clinical symptoms, as well as a lower presence of intubation criteria and a tendency for a lower death rate at day 7, although this last parameter was not statistically different.
Most studies indicating benefits of CPAP or PSV plus PEEP included patients who, on average, had hypercapnia and acidosis indicating acute frank ventilatory failure. A relatively large multicenter study conducted by Nava and colleagues in patients with CPE found major benefits of NIV only in the subgroup of hypercapnic patients, with no significant benefits in terms of ETI rate or outcome in the overall population that included both hypercapnic and normocapnic patients. Despite the long use of NIV in CPE and the publication of guidelines, there is considerable heterogeneity among hospitals regarding its clinical application. Notably, it seems that the higher the experience of the hospital in the use of NIV in CPE the greater the benefit in terms of avoiding patient intubation.
Choice Between CPAP or Pressure Support Plus PEEP
In clinical practice, CPAP is often considered to be easier to apply compared with pressure support plus PEEP. In some small studies in patients with CPE, PSV plus PEEP was more effective than CPAP regarding improvement in physiologic parameters or rapidity of respiratory failure amelioration, but not different in mortality rate or tracheal intubation. In the 3CPO trial both modes of NIV (CPAP or PSV plus PEEP) had similar clinical outcomes. Another clinical study comparing both modes of NIV demonstrated similar results.
In summary, NIV use during CPE seems to be an efficient approach that could reduce mortality, especially in the subgroup presenting with hypercapnia. Conventional medical therapy remains the cornerstone, and NIV, whether it is performed with CPAP or PSV plus PEEP, should be combined with it as soon as possible. CPAP and PSV plus PEEP seem to have similar effects, both in physiologic end points and in clinical outcome, and CPAP can be recommended as a first-line treatment. PSV plus PEEP may be preferred to CPAP in patients with hypercapnia, often associated with comorbidities like COPD or obesity, who are at increased risk of intubation.
Hypoxemic Acute Respiratory Failure
NIV to Prevent Intubation in de Novo Respiratory Failure
The use of NIV in patients with mixed causes of hypoxemic ARF remains debatable. Contrasting results exist between the benefits observed in short-term physiologic studies and in some randomized controlled trials, as well as the high rates of failure in observational studies and the risk of delaying intubation. For instance, one trial in patients with severe pneumonia showed that NIV reduced intubation rate (21% vs. 50%) and ICU length of stay, but this study is often quoted to stress that this benefit was entirely driven by the subgroup of hypercapnic COPD patients. Other RCTs, in nonhypercapnic patients, did not demonstrate any benefit for this indication. By contrast, NIV has also clearly been shown to be beneficial in selected patients with a variety of patterns of hypoxemic respiratory failure, reducing the need for ETI and improving outcomes. In this setting, PSV plus PEEP seems much more efficient than CPAP.
In a large randomized controlled trial of patients with hypoxemic ARF, Delclaux and colleagues showed that the use of CPAP resulted in a greater subjective response and improvement in oxygenation at 1 hour but CPAP did not reduce the need for ETI or improve any clinical outcome. In addition, a few patients suffered from specific complications only observed in the CPAP group, including cardiac arrest at the time of intubation or at the time of mask removal. Antonelli and coworkers showed that NIV using PSV plus PEEP was highly beneficial and associated with fewer adverse effects compared with conventional mechanical ventilation in hypoxemic patients (Pa o 2 /F io 2 < 200 mm Hg). These patients did not have COPD, hemodynamic instability, or neurologic impairment and were randomized when they reached predefined criteria for ETI. Improvements in oxygenation were similar with the two approaches. Despite a 30% failure rate, patients treated with NIV had overall shorter durations of ventilation and ICU stays and experienced fewer complications.
A study performed in three centers by Ferrer and colleagues also included normocapnic patients with persistent hypoxemic ARF and used PSV plus PEEP compared with a standard medical treatment with high-concentration oxygen. Patient selection was rigorous, necessitating clinical cooperation of the patient, no alteration in the state of consciousness, and the absence of organ dysfunction, abundant secretions, cardiac arrhythmias, or ischemia. Patients could have pneumonia, CPE, or immunocompromise. NIV reduced the intubation rate by half and ICU mortality from 39% to 18%. These significant effects were found in the group of patients with pneumonia. Extrapolating these results to individual patients requires the same careful selection process, with exclusion of patients with contraindications. The presence of shock, loss of consciousness, or major secretions should be considered to be contraindications.
However, observational studies describing the use of NIV in pneumonia have often shown high rates of failure. Selection of patients, skills, and experience in the application of NIV and in the decision for intubation may all have contributed to these differences. Great care is required when applying NIV to hypoxemic patients because of the possible disadvantages. In a large observational study on the use of NIV in France, Demoule and colleagues compared the overall results of NIV in patients with acute exacerbation of chronic cardiac or respiratory failure with those with hypoxemic de novo respiratory failure. In the “acute-on-chronic” group, the use of NIV was significantly associated with a better outcome (adjusted OR 0.33). In the de novo group, the use of NIV was not significantly associated with a better or worse outcome. This suggests that NIV should not be used when the risk of failure is high and intubation should not be delayed when clinical signs and symptoms suggest impending NIV failure.
In sum, finding which subgroup of hypoxemic patients is highly likely to benefit from NIV with minimal risk is still a field for investigation. The following categories of patients have been more carefully studied.
NIV for ARDS
Observational studies and subgroup analysis of randomized controlled trials identified ARDS as a strong predictor of NIV failure. A multicenter survey evaluated NIV as first-line therapy in early ARDS patients and found that a higher severity score and a ratio of arterial P o 2 /F io 2 less than or equal to 175 mm Hg 1 hour after initiation of NPPV were independently associated with NIV failure. This survey showed that, with NIV use, ETI was avoided in no more than 50% of patients, even in experienced centers. A recent small prospective, multicenter, randomized controlled trial included 40 patients with mild ARDS. Fewer patients were intubated in the NIV group compared with the control group, and NIV use was associated with less organ failure. The recent Berlin definition of ARDS suggested that NIV may be indicated only in mild ARDS, and not in severe and moderate ARDS, but also emphasized that the role of NIV in ARDS has to be further evaluated. NIV failure in ARDS patients is highly predictable in case of shock, metabolic acidosis, high severity scores of illness, and a greater degree of hypoxemia.
With the H1N1 pandemic, a large number of patients with severe respiratory failure were admitted into ICUs over the world. Many patients developed ARDS requiring intubation and mechanical ventilation and even extracorporeal membrane oxygenation, but NIV was also used widely in these patients with relatively favorable results, albeit with a high rate of failure. This aspect is interesting because after the SARS experience, a concern was raised about the risk of viral transmission during intubation or while using NIV ventilation. Viral transmission did not seem to be an issue in the setting of H1N1, but more data are necessary to completely address this issue.
NIV in Immunocompromised Patients
The prognosis of immunocompromised patients with ARF has clearly improved in the past 15 years. Invasive MV was repeatedly identified as an independent mortality predictor in this population, and the potential to reduce infectious complications was a strong rationale for NIV use in immunocompromised patients. NIV was shown to be beneficial in cancer patients with respiratory failure, and decreased mortality. The first randomized trial in hypoxemic ARF after solid organ transplantation assessed the role of NIV in 40 patients : NIV reduced intubation rate from 70% to 20%, ICU length of stay in survivors, and ICU mortality (20% vs. 50%), with no difference in hospital mortality. Another trial confirmed the benefit of a sequential use of NIV at an early stage in 52 immunocompromised patients with respiratory failure and pulmonary opacities. Intubation rates (46% vs. 77%) and ICU mortality (38% vs. 69%) were reduced in the NIV group. Similarly, early preventive use of CPAP for neutropenic patients with mild respiratory dysfunction prevented subsequent evolution to frank respiratory failure, ICU admission, and the need for intubation.
The generalizability of the results coming from expert centers and their applicability to real-life practice has often been discussed. In an observational study in Italy, NIV was used in 21% of patients with hematologic malignancies requiring ventilatory support. Despite a high failure rate of 46%, NIV was associated with lower mortality than invasive mechanical ventilation after adjustment using a propensity score. Patients intubated from the beginning had a higher severity score but a lower mortality than patients who failed NIV (50% vs. 61%). A trial of NIV as a first-line intervention in selected immunocompromised patients with hypoxemic respiratory failure appears justified but, as stated in a recent editorial, the message is “don’t push too hard!”
In summary, the use of NIV in hypoxemic respiratory failure is supported by a strong rationale. The literature has yielded some conflicting results that probably reflect both the heterogeneity of the underlying diagnoses and some real difficulties in the use of the technique in these patients. Selecting the appropriate patients with pneumonia for a trial of NIV will therefore depend on the experience of the team, on the patients’ cooperation, and on excluding patients with hemodynamic instability, mental status alteration, or abundant secretions.
Prevention of Postoperative Complications
Respiratory complications constitute a major cause of morbidity after surgery, and mortality is often related to reintubation and complications of mechanical ventilation. NIV is becoming increasingly popular for the prevention or treatment of postoperative respiratory complications.
Pathophysiology of Postoperative Respiratory Complications
After thoracic or upper abdominal surgery, the patient’s pulmonary condition can worsen due to residual anesthesia or pain. This is associated with a large reduction in functional residual capacity and transient diaphragmatic dysfunction. Perioperative fluid overload, transfusion-related acute lung injury, inflammation, sepsis, and aspiration may coexist and further worsen respiratory function. Respiratory deficits are maximal in the first hours after surgery and generally recede after 1 or 2 weeks. Because it can restore lung volume, CPAP is frequently used in postoperative patients. Some authors advocate the use of postoperative NIV (CPAP or PSV plus PEEP) for both prophylactic and treatment purposes.
Thoracic Surgery
In the postoperative period following lung resection, pulmonary complications are the leading cause of death. Postoperative MV increases the risk of bronchial stump disruption, bronchopleural fistula, persistent air leaks, and pulmonary infection. NIV was proposed to prevent reintubation, atelectasis, and infection postoperatively after chest surgery. Prophylactic use of NIV preoperatively and postoperatively was shown to improve spirometry and oxygenation in 32 patients at high risk of complications after lung resection surgery. Comparable results have been obtained with prophylactic use of NIV following cardiac surgery: The largest study randomized 500 patients scheduled for elective cardiac surgery to nasal CPAP for at least 6 hours or standard care. The number of pulmonary complications was significantly reduced within the CPAP group, but the reintubation rate was low in both groups. Similar results have been obtained after thoraco-abdominal aortic aneurysm repair.
NIV has also been used for the treatment of respiratory failure after lung surgery. Auriant and colleagues performed a controlled trial in which 48 patients with ARF after lung resection were randomly assigned to NIV or standard treatment. NIV significantly decreased the ETI rate (50% vs. 21%) and hospital mortality (13% vs. 38%), mostly by preventing intubation-related complications. A recent multicenter trial, however, was unable to find any benefit of a systematic administration of NIV in obstructive patients submitted for lung resection. Similarly, the beneficial effect of NIV (lower intubation rate) was suggested in patients with ARF after esophagectomy; in addition, there was no increase in anastomotic leakage. Because the risk of surgical complications induced by positive pressure ventilation is unclear, it is probably wise to keep airway pressures at the lowest effective level.
Abdominal Surgery
NIV can potentially counteract several of the anesthetic and surgical consequences that can explain the high incidence of postoperative hypoxemia after abdominal surgery. Restoring lung volume, preventing atelectasis, improving gas exchange, and decreasing the work of breathing may be achieved through different forms of NIV, including CPAP. Squadrone and colleagues showed that early CPAP delivered by helmet in 209 patients with arterial P o 2 /F io 2 less than 300 at 1 hour after elective major abdominal surgery was able to reduce the intubation rate (1% vs. 10%, P = 0.005), as well as the incidence of pneumonia and sepsis. The ICU and hospital length of stay did not significantly differ. NIV was used in this study with the intention of preventing overt deterioration and more serious complications, suggesting that early use is ideal.
Jaber and colleagues reported that ETI was avoided in 48/72 (67%) patients treated with NIV for acute respiratory failure after abdominal surgery. Arterial P o 2 /F io 2 ratio increased and respiratory rate decreased only in patients who were successfully treated with NIV and avoided ETI. A similar rate of NIV failure in postoperative patients has also been reported in other observational studies.
Trauma Patients
Trauma patients present a high risk of pulmonary dysfunction with subsequent hypoxemic respiratory failure. Compared with a high-flow oxygen mask, the use of NIV has been shown to reduce the intubation rate (12% vs. 40%) and hospital length of stay in a single-center randomized controlled trial of 50 patients with persistent hypoxemia within the first 48 hours after thoracic trauma. NIV may constitute a useful adjunct to manage hypoxemic patients with chest trauma, but adequate analgesia remains of paramount importance in this situation. Larger trials are required to clarify the role of NIV for this indication.
Do-Not-Intubate Patients
NIV is now used frequently in patients in whom intubation is not desirable. Several reports have described the effects of NIV in patients with ARF who were poor candidates for ETI because of advanced age, debilitation, or a “do-not-resuscitate” order. This approach to NIV is feasible and well tolerated, with an overall survival rate of 50% to 70%, depending on the patient population. An important distinction should be made between NIV administered as the upper limit of care versus NIV as part of palliative care to relieve dyspnea at the end of life. Regarding the first indication, NIV offers an interesting possibility to improve a substantial number of patients. Outcomes are better in patients with COPD or pulmonary edema than in purely hypoxemic patients. In a large observational multicenter trial, Azoulay and coworkers assessed patients’ mortality, health-related quality of life and for patients and relatives, signs of anxiety, depression, and posttraumatic stress at 90 days. They compared patients receiving NIV as a ceiling of therapy with patients with no treatment limitation. Hospital mortality in the do-not-intubate group was 46%, but there was no decline at 90 days in health-related quality of life and there were no differences between the two groups in terms of mental health, anxiety, depression, or posttraumatic stress disorder of patients and their relatives. For NIV used in purely palliative care, we have only limited information on its real benefit.
During the Weaning Process and Post-extubation
Weaning
A number of patients with COPD require ETI because they fail NIV, have a contraindication to NIV (such as a need for surgery), or exhibit criteria for immediate ETI. When there is a need for prolonged ventilatory assistance, these patients can be switched to NIV after a few days of ETI to reduce the time of intubation. This approach was examined in several trials with contradictory results. Times to extubation were usually reduced, but this was not consistently translated into a reduction in hospital and ICU stay and mortality. No difference between early NIV weaning and the standard weaning process was reported in several studies. Complications associated with mechanical ventilation, notably pneumonia and sepsis, were either reduced or remained unaffected by this strategy. In the most recent multicenter trial, extubation followed by NIV or extubation followed by standard oxygen therapy were identical with respect to weaning success and reintubation. On the basis of the current evidence, NIV cannot be recommended as an alternative to the standard weaning process.
Post-extubation
NIV has been proposed as a way to minimize reintubations in the approximately 10% to 20% of critically ill patients who fail extubation, even after fulfilling all weaning criteria and having successfully completed a weaning trial. The physiologic rationale for this approach in patients with COPD was well demonstrated by Vitacca and coworkers, who showed equivalent values of the work of breathing under the same ventilatory support delivered before extubation or with NIV after extubation. Several studies addressed the role of NIV in preventing reintubation with unequivocal results. When post-extubation respiratory failure has developed, delivering NIV is often futile and, indeed, may delay reintubation and increase mortality, as suggested by a large multicenter trial of Esteban and associates. By contrast, early delivery of NIV after extubation to prevent subsequent respiratory failure in patients at risk seems to be useful. In patients at high risk of extubation failure, NIV was demonstrated to prevent post-extubation respiratory failure and reintubation in several trials.
A survival benefit of preventive NIV was demonstrated in patients who were hypercapnic during the weaning test. Intubation rates and mortality have been shown to be reduced in high-risk patients (i.e., older than age 65 with cardiac or respiratory comorbidities). These beneficial effects are not observed if NIV is applied routinely in all extubated patients as shown by Su and coworkers, who randomized 406 unselected patients to either NIV or supplemental O 2 mask, early following their extubation. They did not observe any difference in terms of reintubation or mortality rates. In conclusion, in the post-extubation period, NIV can be useful provided the appropriate patient is selected: risk factors for reintubation include underlying cardiac and respiratory disease and/or hypercapnia during the weaning test. NIV should be applied immediately after extubation and before development of respiratory failure.
Preventive Use during Procedures
Bronchoscopy
Flexible bronchoscopy is a relatively invasive procedure with an increased risk of complications in critically ill patients. Bronchoscopy increases work of breathing in spontaneously breathing patients and leads to a decrease in arterial P o 2 by 10 to 20 mm Hg that can persist or even worsen for a few hours after the procedure. Saline instillation for bronchoalveolar lavage and repeated suctioning can lead to a reduction in end-expiratory lung volume. Several feasibility studies showed that NIV with different interfaces can be useful during bronchoscopy in at-risk patients. NIV can prevent alveolar derecruitment and compensate for the extra work of breathing imposed by the procedure. In a randomized trial of 30 hypoxemic patients, CPAP reduced desaturations and the incidence of respiratory failure necessitating ventilatory support (1 vs. 7 patients in the oxygen group). In another trial of 26 hypoxemic patients, during bronchoscopy, arterial P o 2 /F io 2 ratio increased by 82% in the NIV group and decreased by 10% in the standard oxygen group. NIV can help to maintain oxygenation in hypoxemic patients undergoing bronchoscopy. This may translate into a reduction of procedure-related intubations, although more studies are necessary to answer this question.
Endotracheal Intubation
Severe hypoxemia during intubation of hypoxemic patients is common, and the standard bag-mask preoxygenation procedure is often not effective. Baillard and colleagues evaluated 53 patients with significant hypoxemia (arterial P o 2 < 100 mm Hg while on a high F io 2 mask) who required ETI in the ICU. The patients were allocated to 3 minutes of preoxygenation, before ETI, performed using a nonrebreathing bag-valve mask (control group), or PSV plus PEEP (NIV group) used as a preoxygenation method. The NIV group had a statistically significant improvement in pulse oximetry and arterial P o 2 levels with a lower incidence of pulse oximetry saturation values below 80% during the ETI procedure. NIV intolerance requiring its interruption was not observed. A recent review proposed that NIV should be used for preoxygenation and ventilation in patients who cannot reach oxygen saturation greater than 93% to 95% with high F io 2 .
Home Noninvasive Ventilation
Epidemiology
Home NIV refers to the long-term (>3 months) daily application of MV in the home setting through a nasal, oral, or oronasal interface. Prescriptions for home NIV have markedly increased over the past decades as a result of the increasing prevalence of COPD and obesity-hypoventilation syndrome (OHS), although home NIV in COPD patients remains a subject of debate ( Table 102-3 ). Major technologic improvements in ventilators and interfaces, with a progressive shift from volume-cycled to less expensive, lighter, and often more comfortable pressure-cycled ventilators, have also contributed to accelerating this approach. The EuroVent Survey studied patterns of home ventilator use in 16 European countries. The prevalence of patients receiving long-term ventilation varied widely among countries, ranging from 1 to 17/100,000 with an average of 6.6/100,000. Similarly, the relative proportion of patients with neuromuscular, thoracic cage, or lung/airway disorders also differed markedly. Neuromuscular and chest wall disorders were the main indications for NIV in northern Europe, whereas NIV for lung/airway disease was more frequent in southern Europe. Because the prevalence of these conditions presumably does not vary substantially, different patterns of home NIV use probably reflect national policies and differences in the allocation of available resources. Although a similar survey is not available for the U.S. population, extrapolation of the same prevalence suggests that more than 20,000 patients are currently using home NIV in the United States.
