You are in: eMedicine Specialties > Pulmonology > Mechanical Ventilation Ventilation, NoninvasiveArticle Last Updated: May 15, 2006AUTHOR AND EDITOR INFORMATIONSection 1 of 11
 
Author: Sat Sharma, MD, FRCPC, Professor and Head, Division of Pulmonary Medicine, Department of Internal Medicine, University of Manitoba; Site Director, Respiratory Medicine, St. Boniface General Hospital Sat Sharma is a member of the following medical societies: American Academy of Sleep Medicine, American College of Chest Physicians, American College of Physicians-American Society of Internal Medicine, American Thoracic Society, Canadian Medical Association, Royal College of Physicians and Surgeons of Canada, Royal Society of Medicine, Society of Critical Care Medicine, and World Medical Association Editors: Oleh Wasyl Hnatiuk, MD, Program Director, National Capital Consortium, Pulmonary and Critical Ca, Walter Reed Army Medical Center; Associate Professor, Department of Medicine, Uniformed Services University of Health Sciences; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Gregg T Anders, DO, Medical Director, Great Plains Regional Medical Command, Brook Army Medical Center; Clinical Associate Professor, Department of Internal Medicine, Division of Pulmonary Disease, University of Texas Health Science Center at San Antonio; Timothy D Rice, MD, Associate Professor, Departments of Internal Medicine and Pediatrics and Adolescent Medicine, Saint Louis University School of Medicine; Zab Mosenifar, MD, Director, Division of Pulmonary and Critical Care Medicine, Director, Women's Guild Pulmonary Disease Institute, Executive Vice Chair, Department of Medicine, Cedars Sinai Medical Center; Professor of Medicine, David Geffen School of Medicine at UCLA Author and Editor Disclosure Synonyms and related keywords: non-invasive ventilation, noninvasive ventilatory support, non-invasive ventilatory support, noninvasive positive-pressure ventilation, NPPV, negative-pressure ventilation, volume ventilator, pressure-controlled ventilator, bilevel positive airway pressure, BIPAP, bilevel ventilator, continuous positive airway pressure, CPAP, acute respiratory failure, chronic respiratory failure, artificial respiration, body ventilator INTRODUCTIONSection 2 of 11
 
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. —Genesis Noninvasive ventilation is the delivery of ventilatory support without the need for an invasive artificial airway. Such ventilation has a role in the management of acute or chronic respiratory failure in many patients and may have a role for some patients with heart failure. Noninvasive ventilation can often eliminate the need for intubation or tracheostomy and preserve normal swallowing, speech, and cough mechanisms. The use of noninvasive positive-pressure ventilation (NPPV) in acute hospital settings and at home has been steadily increasing. History of noninvasive ventilation The concept of mechanical ventilation first evolved with negative-pressure ventilation. In 1876, Woillez first developed a workable iron lung. In 1889, Alexander Graham Bell designed and built a prototype of iron lung for use with a newborn infant. In the late 1920s, Drinker introduced negative-pressure ventilation and popularized the iron lung. He maintained an 8-year-old girl with acute poliomyelitis on artificial respiration continuously for 122 hours. The polio epidemics of the 1930s, 1940s, and 1950s led to the development of pulmonary medicine as a specialty and the iron lung as a workhorse. Ventilators delivering negative-pressure ventilation fell out of favor as the use of invasive positive-pressure ventilation (PPV) increased during the 1960s. However, over the past decade, a striking resurgence has been observed in the use of noninvasive ventilation, fueled by the development of PPV delivered through a nasal or face mask. MODALITIES OF NONINVASIVE VENTILATIONSection 3 of 11
Negative-pressure ventilation Negative-pressure ventilators support ventilation by lowering the pressure surrounding the chest wall during inspiration and reversing the pressure to atmospheric level during expiration. These devices augment the tidal volume by generating negative extrathoracic pressure. Several of these devices, such as body ventilators and iron lungs, are available and either cover the whole body below the neck or apply negative pressure to the thorax and abdomen. The role of negative-pressure ventilation in the management of acute respiratory failure is unclear. Although studies of body ventilators have shown benefit in patients with chronic obstructive pulmonary disease (COPD), neuromuscular disease, and chest wall deformities who develop acute respiratory failure, prospective and controlled studies are lacking. These devices are not readily accepted by patients because of their awkward size and their propensity to cause upper airway obstructions in some patients. Several uncontrolled studies reported benefits of intermittent negative-pressure ventilation in patients with chronic respiratory failure resulting from chest wall, neuromuscular, or central hypoventilation. However, no benefit was demonstrated in patients with stable but severe COPD. Noninvasive positive-pressure ventilation NPPV is delivered by a nasal or face mask, therefore eliminating the need for intubation or tracheostomy. NPPV can be given by a volume ventilator, a pressure-controlled ventilator, a bilevel positive airway pressure (BIPAP or bilevel ventilator) device, or a continuous positive airway pressure (CPAP) device. Volume ventilators are often not tolerated because they generate high inspiratory pressures that result in discomfort and mouth leaks. NPPV delivers a set pressure for each breath (with a bilevel or standard ventilator in the pressure-support mode). Although positive-pressure support is usually well tolerated by patients, mouth leaks or other difficulties are sometimes encountered. BIPAP ventilators provide continuous high-flow positive airway pressure that cycles between a high positive pressure and a lower positive pressure. NPPV may be used as an intermittent mode of assistance depending on patients' clinical situations. Instantaneous and continuous support is given to the patients in acute respiratory distress. As the underlying condition improves, ventilator-free periods are increased as tolerated, and support is discontinued when the patient is deemed stable. In most studies, the duration of NPPV use in patients with acute on chronic respiratory failure averages 6-18 hours. The total duration of ventilator use varies with the underlying disease; approximately 6 hours is used for acute pulmonary edema and more than 2 days is used for COPD exacerbation. Honrubia et al compared the efficacy and resource consumption of NPPV against conventional mechanical ventilation in patients with acute respiratory failure. Avoidance of intubation, mortality, and consumption of resources were the outcome variables. Thirty-one patients were assigned to the noninvasive group, and 33 were assigned to the conventional group. NPPV reduced the need for intubation in patients with ARF from different causes. A trend of reduction in ICUs and hospital mortality together with fewer complications during ICU stay was observed (Honrubia, 2005). GENERAL TECHNICAL ISSUESSection 4 of 11
Mechanisms of action NPPV decreases the work of breathing and thereby improves alveolar ventilation while simultaneously resting the respiratory musculature. The improvement in gas exchange with BIPAP occurs because of an increase in alveolar ventilation. Externally applied expiratory pressure (eg, positive end-expiratory pressure [PEEP]) decreases the work of breathing by partially overcoming the auto-PEEP, which is frequently present in these patients. The patients generate a less negative inspiratory force to initiate a breathing cycle. Inhalation and exhalation In spontaneous mode, upon detection of inspiration, higher pressure is delivered until the flow rate falls below the threshold level. The expiratory pressure with bilevel pressure support is equivalent to the PEEP, and the inspiratory pressure is equivalent to the sum of the PEEP and the level of pressure support. In timed mode, biphasic positive airway pressure ventilation alternates between the inspiratory and expiratory pressures at fixed time intervals, which allows unrestricted breathing at both pressures. This differs from the spontaneous mode of BIPAP, which cycles on the basis of the flow rates of the patient's own breathing. Supplemental oxygen can be connected to the device, but a higher flow of oxygen therapy is usually required. NPPV is more effective in a relaxed patient and is not optimal in an anxious uncooperative patient or a patient fighting the ventilator. Patients must be adequately prepared with properly fitting masks, and the increase of the inspiratory and the expiratory pressures should occur gradually. Effectiveness should be determined clinically by improved respiratory distress, decreased patient discomfort, and improved results from arterial blood gas determinations. BIPAP ventilator versus conventional ventilator The BIPAP ventilator has been used in randomized trials with good results. However, the conventional ventilator offers a number of advantages, such as the delivery of precise oxygen concentrations and separate inspiratory and expiratory tubing that minimizes carbon dioxide rebreathing. Patient disconnection can be readily detected because monitoring and alarm features are more sophisticated in conventional ventilators than in bilevel systems. Nasal mask versus face mask No randomized trials have compared nasal masks to full face masks in NPPV. Most patients in acute respiratory failure are mouth breathers; therefore, a facial mask may be preferable in some patients. These patients should be carefully observed because of the risk of aspiration. Patient selection Patients who are in acute respiratory distress and are at risk of needing intubation should be selected for noninvasive ventilation if they have a reversible cause of acute respiratory failure. Guidelines for the use of NPPV in patients with acute respiratory failure
Protocol for Initiation of NPPV in patients with acute respiratory failure
Weaning from NPPV In stable patients, weaning from NPPV may be accomplished either by progressively decreasing the levels of positive airway pressure or by discontinuing the therapy for increasing lengths of time. A combination of both strategies can also be used. NPPV IN ACUTE EXACERBATION OF COPDSection 5 of 11
Acute exacerbation of COPD is a frequent cause of admission to the hospital and to the intensive care unit (ICU). Patients develop a deterioration of gas exchange accompanied by rapid shallow breathing, severe dyspnea, right ventricular failure, and encephalopathy. The respiratory system is unable to maintain adequate alveolar ventilation in the presence of abnormalities in respiratory mechanics. Patients develop a shortened inspiratory time, decreased in tidal volume, and increased respiratory frequency of the excessive respiratory load. Therefore, treatment should be directed at reducing the loads imposed on the respiratory muscles. Benefits of NPPV In acute respiratory failure, NPPV offers a number of potential advantages over invasive PPV. These advantages include the avoidance of intubation-related trauma, a decreased incidence of nosocomial pneumonia, enhanced patient comfort, a shorter duration of ventilator use, a reduction in hospital stay, and ultimately, reduced cost. Clinical trials supporting the use of NPPV in patients with COPD exacerbation NPPV is an effective means of treating patients with acute respiratory failure resulting from a variety of causes, as demonstrated by uncontrolled studies and prospective randomized trials. NPPV improves alveolar ventilation by increasing tidal volume. Most studies have used NPPV as an intermittent mode of support because the support is not delivered on a continuous basis, but rather for 6-18 h/d. The duration of NPPV depends on each patient's clinical situation. Most trials used inspiratory pressures of 12-20 cm water and expiratory pressures of 0-6 cm water and excluded patients with hemodynamic instability, uncontrolled arrhythmia, or a high risk of aspiration. Recent prospective randomized studies strongly support the use of noninvasive mechanical ventilation in patients with severe exacerbations of COPD. In a large randomized trial (Brochard, 1995) comparing NPPV with a standard ICU approach, the use of NPPV was shown to reduce complications, the duration of ICU stay, and mortality. Patients in whom NPPV failed had a similar mortality rate compared to the intubated group (25% vs 30%). Plant and colleagues recently published the largest prospective randomized study comparing NPPV to standard treatment in patients with COPD exacerbation. NPPV was administered on the ward; the nurses were trained for 8 hours in the preceding 3 months. Treatment failed in significantly more patients compared to the control group (27% vs 15%); in-hospital mortality rates were significantly reduced from the use of NPPV (20% to 10%). In addition, 3 Italian cohort studies with historical or matched control groups have suggested that long-term outcome of patients treated with NPPV is much better than that of patients treated with medical therapy and/or with endotracheal intubation. Cochrane Systematic Review determined the efficacy of NPPV in the management of patients with respiratory failure due to an acute exacerbation of COPD. Fourteen studies were included in the review. NPPV resulted in decreased mortality (relative risk [RR] 0.52), decreased need for intubation (RR 0.41), and reduction in treatment failure (RR 0.48). The complications associated with treatment (RR 0.38) and length of hospital stay (mean, 3.24 d) was also reduced in the NPPV group. NPPV has benefit as first-line intervention in addition to usual medical care in all appropriate patients for the management of respiratory failure secondary to an acute exacerbation of COPD. Early NPPV is known to reduce the likelihood of endotracheal intubation, treatment failure, and mortality (Ram, 2004). Early use of NPPV to assess the outcomes of acute exacerbation of COPD was evaluated in those patients with respiratory muscle fatigue and mild respiratory insufficiency. The early use of NPPV on general ward improved arterial blood gas and respiratory pattern and decreased the rate of need for intubation in AECOPD patients. Severely altered level of consciousness (ALC) has been considered a contraindication to NPPV. A recent study compared the clinical outcome of patients with ARF due to COPD exacerbations and different degrees of ALC. This study confirmed that NPPV was successfully applied to patients experiencing COPD exacerbations with milder ALCs, whereas the rate of failure in patients with severely ALCs was higher, but an initial and cautious attempt with NPPV may be performed (Scala, 2004). A step-wise approach to the management of acute COPD exacerbation A summary of all these studies shows that NPPV has been shown to offer better outcomes to patients admitted with acute exacerbations of COPD. A complimentary step-wise approach to these patients is recommended:
The use of NPPV does not require longer nursing time, but longer respiratory therapist time is required in the initial period, as compared to the conventional treatment. In a recent study in which NPPV was used on the ward, NPPV was applied by the ward nurses without the therapist assistance. These patients required a half an hour of extra nursing time in the first 8 hours, which decreased on subsequent days. NPPV IN HYPOXEMIC RESPIRATORY FAILURESection 6 of 11
NPPV refers to the delivery of mechanical ventilation using techniques that do not require an endotracheal airway. The recent increase in NPPV use in acute case settings has been fueled by the desire to reduce the complications resulting from intubation and invasive ventilation. These complications are upper airway trauma, arrhythmia, hypertension, aspiration of gastric contents, sinusitis, pneumonia, and patients' loss of their ability to eat and communicate verbally. By avoiding these complications, NPPV has the potential to reduce hospital morbidity, facilitate weaning from mechanical ventilation, and shorten the duration of hospitalization, thereby improving patient comfort. Studies on the use of NPPV in hypoxemic respiratory failure, defined as PaO2-to-FIO2 ratio of less than 200 in the absence of carbon dioxide retention, have yielded conflicting results. Patients with a variety of diagnoses (eg, pneumonia, congestive heart failure, acute respiratory distress syndrome) had been included in this category. Uncontrolled studies have suggested that some patients with hypoxemic respiratory failure may respond favorably to NPPV. In one study of NPPV for hypoxemic respiratory failure, only 30% of NPPV-treated patients required intubation. The mortality rate was 22%, compared to the predicted mortality rate of 40%. In a trial of 64 patients with hypoxemic respiratory failure randomized to receive NPPV or intubation, only 31% of NPPV-treated patients required intubation. Improvements in oxygenation were comparable in the 2 groups, but the NPPV-treated patients had significantly fewer infectious complications. In another study of patients with severe community-acquired pneumonia and hypoxemic/hypercapnic respiratory failure, NPPV use was associated with reduced intubation rates (21% vs 50%) and a reduced duration of ICU stay (1.8 d vs 6 d) compared with standard treatment. The use of NPPV in patients with hypoxemic respiratory failure appears to be quite encouraging, but further investigations are needed to establish the efficacy of noninvasive ventilation. A recent meta-analysis assessed the effect of NPPV on the rate of endotracheal intubation, ICU and hospital length of stay, and mortality for patients with acute hypoxemic respiratory failure not due to cardiogenic pulmonary edema. Use of NPPV to standard care in the setting of acute hypoxemic respiratory failure reduced the rate of endotracheal intubation (absolute risk reduction 23%), ICU length of stay (absolute reduction 2 d), and ICU mortality (absolute risk reduction 17%). Because the effectiveness varied among different populations, the literature does not support the routine use of NPPV in all patients with acute hypoxemic respiratory failure (Keenen, 2004). NPPV IN OTHER CAUSES OF ACUTE RESPIRATORY FAILURESection 7 of 11
Controlled studies are generally lacking in the support of using NPPV for other types of acute respiratory failure. However, several case series report successful NPPV use in acute asthma, cystic fibrosis, respiratory deterioration following extubation in the postoperative phase, acute pulmonary edema, and as a method of weaning patients from invasive ventilation. Acute pulmonary edema Noninvasive CPAP has been shown in randomized controlled trials to be an effective therapy for acute pulmonary edema, improving oxygenation and hypercapnia, decreasing respiratory work, and reducing the rate of endotracheal intubation. In a controlled study, nasal BIPAP improved the PaCO2 levels, pH, respiratory rate, and dyspnea more rapidly than nasal CPAP in patients with acute pulmonary edema. Therefore, CPAP alone seems a logical first choice in the treatment of patients with acute pulmonary edema. However, patients with hypercapnia or patients with continued respiratory distress on CPAP should be switched to BIPAP. One randomized trial compared the effects of oxygen, continuous positive airway pressure (CPAP), and bilevel positive airway pressure (BIPAP) on the rate of endotracheal intubation in patients with acute cardiogenic pulmonary edema. Compared with oxygen therapy, CPAP and BIPAP resulted in similar vital signs and arterial blood gases and a lower rate of endotracheal intubation (Park, 2004). A recent systematic review analyzed the short-term effect of noninvasive ventilation on major clinical outcomes in patients with acute cardiogenic pulmonary edema. Fifteen trials were selected, noninvasive ventilation significantly reduced the mortality rate by nearly 45% compared with conventional therapy. There was also a significant decrease in the "need to intubate" rate. However, CPAP or BIPAP showed no differences in intubation or mortality rates in the analysis of studies comparing the 2 techniques (Masip, 2005). Acute asthma No randomized trials have evaluated NPPV to treat acute asthma. In the largest uncontrolled trial, 17 patients with asthma who had an average initial pH of 7.25 and a PaCO2 of 65 mm Hg were treated with NPPV. Only 2 patients required intubation for hypercapnia. The average duration of ventilation was 16 hours, and no complications occurred. Therefore, NPPV appears to be an effective ventilatory modality in correcting gas exchange abnormalities in patients with severe asthma exacerbation. Cystic fibrosis One study described the use of NPPV to treat 6 patients with end-stage cystic fibrosis with forced expiratory volumes in one second (FEV1) ranging from 350-800 mL with severe acute or chronic carbon dioxide retention. Patients were supported for 3-36 days. Four of these patients survived until a heart or lung transplant could be performed. Therefore, NPPV could be used as a rescue therapy in supporting patients with acute and deteriorating cystic fibrosis to provide a bridge to transplantation. Facilitation of weaning NPPV has been used to accelerate and facilitate weaning in patients who do not meet the standard criteria for extubation. Patients in whom weaning is difficult have been placed on NPPV following extubation; thereafter, weaning is continued by increasing the length of ventilator-free periods. Some of these patients may only require nocturnal assistance for variable periods. However, this approach should be offered only to carefully selected patients. Although the selection criteria have not been well defined, they include a patient who is fully alert and cooperative, an airway that is easy to reintubate, and a patient with respiratory muscle strength sufficient to clear secretions. A recent meta-analysis summarized the evidence available to utilize NPPV for weaning and demonstrated a consistent benefit. The outcomes evaluated were weaning mortality, ventilator-associated pneumonia, and the total duration of mechanical ventilation among invasively ventilated adults with respiratory failure. Five studies enrolling 171 patients demonstrated that, compared with invasive ventilation, noninvasive weaning decreased mortality (RR, 0.41), ventilator-associated pneumonia (RR, 0.28), and the total duration of mechanical ventilation (mean difference, -7.33 d). Patients who have developed acute and chronic respiratory failure because of obesity hypoventilation syndrome may often be switched from invasive ventilation to NPPV support. Because these patients require ongoing ventilatory support initially 24 h/d and subsequently through the nights, weaning via NPPV appears to be the best option. NPPV weaning has been used in these patients, tracheostomy notwithstanding. Another use of NPPV is in the treatment of extubation failures. These patients often have planned extubations, which fail because the patient may not have completely recovered from the underlying cause of respiratory failure. A trial of NPPV may be given to these patients; most benefit appears to be in patients with COPD exacerbations, acute pulmonary edema, and postextubation upper airway obstruction secondary to glottic swelling. NPPV IN CHRONIC RESPIRATORY DISORDERSSection 8 of 11
Restrictive thoracic disorders Several uncontrolled studies, including those by Ellis et al, Kerby et al, and Bach et al, demonstrated that even patients with severe carbon dioxide retention and symptoms such as morning headache and daytime hypersomnolence could undergo remarkable reversal after several weeks of nocturnal nasal ventilation. Uncontrolled trials have consistently demonstrated the efficacy of NPPV in restrictive thoracic disorders, but no randomized trial has ever been conducted. The long-term survival of patients with restrictive thoracic diseases who use NPPV for chronic respiratory failure is comparable to those who use invasive PPV. Noninvasive ventilation (NIV) is being used increasingly in patients with chronic neuromuscular disorders; however, more studies are needed to determine the optimal mode of ventilation. Chadda et al compared physiological short-term effects of assist/controlled ventilation (ACV) and two pressure-limited modes (pressure-support ventilation [PSV] and assist pressure-controlled ventilation [ACPV]) in patients with stable neuromuscular disease who needed NIV. Noninvasive ACV, ACPV, and PSV had similar effects on alveolar ventilation and respiratory muscle unloading, despite some differences in the pattern of breathing (Chadda, 2004). Initiation of NPPV In patients with progressive neuromuscular diseases, NPPV should be initiated at the onset of daytime hypoventilation and symptoms; early institution may be advantageous in slowing the progression of respiratory failure. When the ventilator-free time becomes short, most investigators prefer instituting invasive PPV, although some have advocated using NPPV, even when patients require continuous ventilatory support. Guidelines for use of NPPV in chronic respiratory failure resulting from restrictive processes
Severe but stable COPD Evidence for the use of NPPV in patients with severe but stable COPD is less convincing. Enthusiasm was initially generated in the 1980s by the hypothesis that the intermittent use of negative-pressure ventilation in patients with severe but stable COPD would improve overall function by resting chronically fatigued respiratory muscles. Subsequent controlled studies have demonstrated no significant benefit. Of the 4 controlled studies using NPPV for severe but stable COPD, only 1 has shown favorable results. This crossover study by Meecham Jones used a nasal BIPAP system nocturnally, and improvements were observed in daytime and nocturnal PaCO2, total sleep time, and quality-of-life scores after 3 months of NPPV use. Patients enrolled in this study had an average PaCO2 of 57 mm Hg and an FEV1 of 821 mL. Many patients with severe chronic COPD do not tolerate long-term PPV. A trial of nocturnal NPPV is recommended in patients with COPD with severe hypercapnia (PaCO2 >55 mm Hg), nocturnal oxygen desaturation, coexisting sleep disordered breathing, and possibly patients with frequent panic attacks, which may be relieved by using NPPV. COMPLICATIONS, PITFALLS, AND CONTROVERSIESSection 9 of 11
Complications of NPPV Few complications are associated with NPPV. The most common problem is local damage to facial tissue because of the pressure effects of the mask and straps. Mild gastric distension may occur but is not significant, and removal of the nasogastric tube is not warranted. Eye irritation and sinus pain or congestion may also occur. Barotrauma is uncommon. Modest air leaks at the facial seal are common but do not decrease the benefit patients receive from NPPV. Adverse hemodynamic effects resulting from NPPV are unusual, although preload reduction and hypotension may occur. Patients on noninvasive ventilation must be carefully monitored and attention should be given to their comfort, the possibility of them developing dyspnea, their respiratory rate, and their oxyhemoglobin saturation. For a variety of reasons, noninvasive ventilation techniques are not always successful. Hemodynamic instability, deteriorating mental status, and an increasing respiratory rate indicate failure. Increasing respiratory acidosis, the inability to maintain adequate oxygen saturation, and problems with respiratory secretions can limit the success of this technique. Patients who refuse intubation or in whom intubation is contraindicated In one study of 30 patients with respiratory failure in whom endotracheal intubation was contraindicated, NPPV was successful in 60%. Another uncontrolled series showed similar response to NPPV among 26 patients who refused intubation. Based on these findings, the use of NPPV for patients who are not to be intubated is justifiable as long as the patient understands that NPPV is a form of life support. However, this therapy should only be offered if a reversible superimposed acute process is present, and it should not be used indiscriminately to prolong the dying process. Pitfalls and controversy Patients should be selected using established guidelines. Centers lacking experience in the application of these devices should make efforts to educate their respiratory care staff. More clinical research is needed before NPPV can be used to its greatest advantage. Advances in interface and ventilator technology are likely to enhance patient tolerance. Further prospective studies of clinical applications, such as the use of noninvasive ventilation in patients with severe but stable COPD or in those with non-COPD forms of acute respiratory failure, will better define populations of patients likely to benefit from noninvasive ventilation. MULTIMEDIASection 10 of 11
REFERENCESSection 11 of 11
Ventilation, Noninvasive excerpt Article Last Updated: May 15, 2006 | ||||||||||||||||||||||||||||||||||||||||||
