Noninvasive Ventilation

Noninvasive ventilation refers to the delivery of assisted ventilatory support without the use of an endotracheal tube. Noninvasive positive pressure ventilation (NPPV) can be delivered by using a volume-controlled ventilator, a pressure-controlled ventilator, a bilevel positive airway pressure ventilator, or a continuous positive airway pressure device. During the past decade, there has been a resurgence in the use of noninvasive ventilation, fueled by advances in technology and clinical trials evaluating its use. Several manufacturers produce portable devices that are simple to operate. This review describes the equipment, techniques, and complications associated with NPPV and also the indications for both short-term and long-term applications. NPPV clearly represents an important addition to the techniques available to manage patients with respiratory failure. Future clinical trials evaluating its many clinical applications will help to define populations of patients most apt to benefit from this type of treatment. Noninvasive ventilation refers to the delivery of assisted ventilatory support without the use of an endotracheal tube. Noninvasive positive pressure ventilation (NPPV) can be delivered by using a volume-controlled ventilator, a pressure-controlled ventilator, a bilevel positive airway pressure ventilator, or a continuous positive airway pressure device. During the past decade, there has been a resurgence in the use of noninvasive ventilation, fueled by advances in technology and clinical trials evaluating its use. Several manufacturers produce portable devices that are simple to operate. This review describes the equipment, techniques, and complications associated with NPPV and also the indications for both short-term and long-term applications. NPPV clearly represents an important addition to the techniques available to manage patients with respiratory failure. Future clinical trials evaluating its many clinical applications will help to define populations of patients most apt to benefit from this type of treatment. Noninvasive ventilation refers to the delivery of assisted ventilatory support without the use of an endotracheal tube. Historically, the first methods of ventilatory support were entirely noninvasive. These devices used negative extrathoracic pressure to support ventilation by exposing the chest wall to subatmospheric pressure during inspiration, with expiration occurring as the pressure around the chest wall is allowed to return to atmospheric levels. The prototypical negative pressure ventilator is the iron lung (Drinker respirator), which was used widely during the 1950s to treat respiratory failure associated with the poliovirus epidemic. Use of noninvasive methods of mechanical ventilation decreased during the 1960s as the use of endotracheal tubes and positive pressure ventilation gained broad acceptance. Interest in noninvasive ventilators reemerged during the early 1980s when nocturnal use of negative pressure ventilators was reported to reverse daytime gas exchange abnormalities and symptoms of chronic hypoventilation in patients with neuromuscular diseases and chronic obstructive pulmonary disease (COPD). During the past decade, there has been a resurgence in the use of noninvasive ventilation, fueled by advances in technology and clinical trials evaluating its use. This review describes the equipment, techniques, and complications associated with noninvasive positive pressure ventilation (NPPV) as well as the indications for both short-term and long-term applications. Noninvasive positive airway pressure treatment of obstructive sleep apnea has been discussed in a consensus statement1Loube DI Gay PC Strohl KP Pack AI White DP Collop NA Indications for positive airway pressure treatment of adult obstructive sleep apnea patients: a consensus statement.Chest. 1999; 115: 863-866Crossref PubMed Scopus (325) Google Scholar and a review article2Strollo Jr, PJ Sanders MH Atwood CW Positive pressure therapy.Clin Chest Med. 1998; 19: 55-68Abstract Full Text Full Text PDF PubMed Scopus (52) Google Scholar and thus will not be discussed in this article. Noninvasive positive pressure ventilation involves the use of a mechanical ventilator connected by tubing to an interface that directs airflow into the nose or the nose and mouth. The interface consists of a silicone mask or a mouthpiece. Head straps are used to secure the mask to the patient (Figure 1). Many masks are available, including full-face masks that cover the nose and mouth, nasal masks that cover the nose only, and “nasal pillows” that fit into the nostrils.3Meduri GU Noninvasive positive-pressure ventilation in patients with acute respiratory failure.Clin Chest Med. 1996; 17: 513-553Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar Several manufacturers produce portable devices that are simple to operate. In the hospital setting, patients may undergo ventilation noninvasively with a portable device or with a standard ventilator. Noninvasive positive pressure ventilation can be delivered by using a volume- or pressure-cycled ventilator, a bilevel positive airway pressure (PAP) ventilator, or a continuous positive airway pressure (CPAP) device.4Hillberg RE Johnson DC Noninvasive ventilation.N Engl J Med. 1997; 337: 1746-1752Crossref PubMed Scopus (159) Google Scholar Volume-controlled noninvasive ventilators deliver a set volume for each breath. Patient tolerance of this mode is often poor because the inspiratory pressure may be increased; this can be uncomfortable and cause air leaks around the mask. Positive pressure noninvasive ventilation, in which the ventilator delivers a set pressure for each breath, is commonly administered with bilevel PAP ventilators or with standard ventilators that use pressure support or pressure control modes. Bilevel PAP ventilators provide continuous PAP that allows independent control of inspiratory and expiratory pressures. When a patient initiates inhalation, the ventilator senses a change in the flow of gas through the circuit. After this is sensed, the gas (typically a mixture of room air supplemented with oxygen as needed) is applied with the predetermined amount of inspiratory pressure. Similarly, when the ventilator recognizes a decrease in the inspiratory flow of gas to a threshold value, the pressure is reduced to the expiratory pressure. Bilevel PAP can be administered in a spontaneous setting, a timed setting, or both. The spontaneous setting requires the patient to initiate every breath. In the timed setting, the machine cycles between inspiration and expiration based on preset timing intervals independent of patient effort. The combined spontaneous/timed setting allows the caregiver to determine a minimal respiratory rate. If the ventilator does not detect a spontaneous breath within a predetermined time interval, it will automatically cycle into inspiration. Continuous positive airway pressure delivers a continuous positive pressure throughout the respiratory cycle and is effective only if the patient is breathing spontaneously. It cannot provide ventilation if the patient becomes apneic. A hospital setting, commonly a respiratory ward or a monitored unit with an experienced respiratory care team, is necessary to initiate NPPV for more acute respiratory failure. Ideal candidates for NPPV are patients who are cooperative and hemodynamically stable. For patients with chronic types of respiratory failure, therapy is initiated in the home with the aid of skilled therapists or in a facility-based sleep laboratory during an overnight stay. Complications of NPPV include nasal congestion, facial skin reddening, eye irritation, nasal bridge ulceration, aspiration, and gastric distention.5Mehta S Hill NS Noninvasive ventilation in acute respiratory failure.Respir Care Clin N Am. 1996; 2: 267-292PubMed Google Scholar The use of a protective synthetic covering (Duoderm) on the bridge of the nose helps to prevent skin breakdown and reduce the incidence of nasal bridge ulceration. When gastric distention occurs, a nasogastric tube can be used to relieve the distention while still allowing the mask to seal. Nasal congestion is common with long-term use. This is treated with in-line humidifiers, topical nasal corticosteroids, or topical anticholinergics. Acute Respiratory Failure Due to COPD.—A systematic review and a meta-analysis of controlled trials examining the use of NPPV in patients with acute respiratory failure due to COPD exacerbations provide strong evidence that NPPV decreases the need for endotracheal intubation (odds ratio [OR], 0.20; 95% confidence interval [CI], 0.11-0.36) and decreases mortality (OR, 0.29; 95% CI, 0.15-0.59).6Keenan SP Kcrnerman PD Cook DJ Martin CM McCormack D Sibbald WJ Effect of noninvasive positive pressure ventilation on mortality in patients admitted with acute respiratory failure: a mela-analysis.Crit Care Med. 1997; 25: 1685-1692Crossref PubMed Scopus (261) Google Scholar These trials also demonstrated that patients treated with NPPV have fewer complications, and length of time in the intensive care unit (ICU) and hospital is briefer. The criteria used to select patients to receive NPPV are based on published studies demonstrating its efficacy. Generally, in patients with respiratory distress due to a COPD exacerbation, NPPV should be initiated before severe symptoms develop. Symptomatic patients with increased Paco2 levels are ideal candidates for NPPV. Contraindications for the use of NPPV include respiratory arrest, evidence of acute cardiac ischemia or acute myocardial infarction, need for airway protection, impaired mental status, and inability to fit or wear the mask properly because of severe claustrophobia or facial abnormalities. Acute Respiratory Failure Not Related to COPD.— Several case series have suggested that NPPV is an effective means of ventilation for patients with acute hypoxic respiratory failure. In addition, 2 randomized controlled trials used NPPV in patients with acute hypoxic respiratory failure. Wysocki et al7Wysocki M Trie L Wolff MA Millet H Herman B Noninvasive pressure support ventilation in patients with acute respiratory failure: a randomized comparison with conventional therapy.Chest. 1995; 107: 761-768Crossref PubMed Scopus (344) Google Scholar randomized nonintubated patients with acute respiratory failure to receive either conventional therapy or NPPV. They found no statistical difference in the rate of endotracheal intubation, hospital survival, or length of stay in the ICU. In a post hoc analysis of 17 patients with hyper-capnia (Paco2 >45 mm Hg), those treated with NPPV had fewer rates of endotracheal intubation (36% vs 100%; P = .02), briefer stays in the ICU (13 ± 15 days vs 32 + 30 days; P = .04), and fewer deaths (9% vs 66%; P = .06) compared with those who received conventional therapy. The hypothesis generated in this post hoc analysis is that NPPV is more effective in patients with severe hypercapnia. A randomized trial by Antonelli et al8Antonelli M Conti G Rocco M et al.A comparison of noninvasive positive-pressure ventilation and conventional mechanical ventilation in patients with acute respiratory failure.N Engl J Med. 1998; 339: 429-435Crossref PubMed Scopus (849) Google Scholar involved 64 patients with hypoxemic respiratory failure who were treated with conventional mechanical ventilation or NPPV. They demonstrated that NPPV was as effective as conventional ventilation in improving gas exchange measurements during the first hour of ventilation. The frequency of total complications and the frequency of pneumonia or sinusitis were higher in the conventional ventilation group compared with the NPPV group (66% vs 38%, P = .02, and 31% vs 3%, P = .003, respectively). The mean ± SD length of stay in the ICU was briefer for patients in the NPPV group vs those in the conventional treatment group (9 ± 7 days vs 16 ± 17 days, respectively; P = .04). No difference was noted in the number of patients who survived their stay in the ICU in the conventional ventilation group compared with the NPPV group (OR, 0.4; 95% CI, 0.1-1.4). To date, the randomized controlled trials investigating the use of NPPV in acute respiratory failure due to causes other than COPD provide preliminary information to guide the use of NPPV for these patients. More controlled studies are necessary. Asthma Exacerbation and Status Asthmaticus.— Only 1 randomized controlled trial involving the use of NPPV in the treatment of an asthma exacerbation has been reported.9Pollack Jr, CV Fleisch KB Dowsey K Treatment of acute bronchospasm with bcta-adrenergic agonist aerosols delivered by a nasal bilevel positive airway pressure circuit.Ann Emerg Med. 1995; 26: 552-557Abstract Full Text Full Text PDF PubMed Scopus (102) Google Scholar In this trial, patients with mild to moderate asthma were randomized to receive their first 2 treatments with a ß-agonist with or without NPPV. Although the peak expiratory flow rate improved in the group treated with NPPV, none of the patients required intubation; no information was given about length of hospital stay. Noncontrolled studies of NPPV to treat status asthmaticus have demonstrated an improvement in gas exchange, and the rate of patients who required endotracheal intubation was low. However, without an appropriate control group, inferences about the effects of treatment are limited. A randomized trial that will completely assess the role of NPPV in status asthmaticus is under way. Cardiogenic Pulmonary Edema.—Randomized controlled trials of the use of CPAP vs oxygen in patients with cardiogenic pulmonary edema suggest that. CPAP improves oxygenation and hypercapnia and decreases the need for endotracheal intubation and the length of stay in the ICU.10Bersten AD Holt AW Vedig AE Skowronski GA Baggoley CJ Treatment of severe cardiogenic pulmonary edema with continuous positive airway pressure delivered by face mask.N Engl J Med. 1991; 325: 1825-1830Crossref PubMed Scopus (530) Google Scholar, 11Lin M Yang YF Chiang HT Chang MS Chiang BN Cheitlin MD Reappraisal of continuous positive airway pressure therapy in acute cardiogenic pulmonary edema: short-term results and long-term follow-up.Chest. 1995; 107: 1379-1386Crossref PubMed Scopus (281) Google Scholar In a trial comparing CPAP to bilevel PAP, no significant differences were found with respect to intubation requirement, length of stay in the ICU or hospital, or mortality.12Mehta S Jay GD Woolard RH et al.Randomized, prospective trial of bilevel versus continuous positive airway pressure in acute pulmonary edema.Crit Care Med. 1997; 25: 620-628Crossref PubMed Scopus (416) Google Scholar An interim analysis, however, revealed a higher incidence of myocardial infarction in the group treated with bilevel PAP vs CPAP (71% vs 31%; P = .02). Thus, the investigators concluded that further trials are necessary to clarify the effects of NPPV on hemodynamics and infarction rates in these patients. Chronic Respiratory Failure Due to Neuromuscular Disease, Thoracic Deformities, and Idiopathic Hypo-ventilation.—Most of the studies involving NPPV in patients with chronic respiratory failure due to neuromuscular diseases, thoracic deformities, and idiopathic hypoventilation are noncontrolled cohort studies. These studies consistently demonstrated that use of nocturnal NPPV improved gas exchange abnormalities, alleviated daytime symptoms, and ameliorated nocturnal hypoventilation and oxygen desaturation.13Hill N Noninvasive ventilation.Pulm Perspect. September 1997; 14: 1-4Google Scholar Despite the lack of prospective, controlled trials evaluating the use of NPPV in these patients, nocturnal NPPV is widely accepted as the ventilatory mode of choice in patients with chronic respiratory failure due to neuromuscular disease, thoracic deformities, and idiopathic hypoventilation. The use of NPPV in these patients has eliminated the need for a tracheostomy and has improved many patient-centered outcomes. A European Consensus Conference suggested that NPPV should be instituted in patients with neuromuscular disorders when any of the following symptoms are present: morning headache, daytime hypersomnolence, nocturnal sleep difficulties, or cognitive dysfunction.14Robert D Willig TN Leger P Long-term nasal ventilation in neuromuscutar disorders: report of a consensus conference [published correction appears J Eur Respir J. 1993:6:1233].Ear Respir J. 1993; 6: 599-606PubMed Google Scholar In the absence of symptoms, institution of NPPV is recommended when the Paco2 is higher than 45 mm Hg or the Pao2 is less than 60 mm Hg on a morning arterial blood gas study or when pronounced nocturnal desaturation occurs. In addition to an arterial blood gas study, measurement of the forced vital capacity and maximal respiratory pressures and an overnight pulse oximetry are useful. Once treatment is indicated, the patient is fitted for the appropriate mask or mouthpiece and then monitored to determine the appropriate mode and settings of NPPV. Because patient compliance is crucial for benefit, follow-up visits are indicated to monitor symptoms and gas exchange abnormalities. Severe Stable COPD.—Controversy exists regarding the efficacy of NPPV in patients with severe stable COPD.15Meyer TJ Hill NS Noninvasive positive pressure ventilation to treat respiratory failure.Ann Intern Med. 1994; 120: 760-770Crossref PubMed Scopus (180) Google Scholar Early noncontrolled studies showed that arterial blood gas measurements improved in patients with COPD who were treated with NPPV. Patients who showed benefit were those who also had pronounced daytime hypercapnia and in whom nocturnal hypercapnia could be successfully reduced with overnight ventilation. Randomized controlled trials reported conflicting results when NPPV was used to provide intermittent ventilatory assistance to patients with severe stable COPD compared with oxygen alone. Poor patient compliance with the equipment was reported in several studies. Some of the disparate results among controlled trials may have been due to differences in patient populations. Studies showing benefits with NPPV enrolled patients with more severe gas exchange abnormalities compared with studies demonstrating no benefit. The results of a multicenter European study on long-term outcome and survival with NPPV in patients with COPD compared with supplemental oxygen alone are awaited to provide additional evidence to guide clinical use. Additional guidelines for the use of NPPV in the home will be in a consensus statement by the National Association for Medical Direction of Respiratory Care.16Clinical indications for non-invasive positive pressure ventilation in chronic respiratory failure due to restrictive lung disease, COPD, and nocturnal hypoventilation: a consensus conference report by the National Association for Medical Direction of Respiratory Care. Chest. In press.Google Scholar Noninvasive positive pressure ventilation clearly represents an important addition to the techniques available to manage patients with respiratory failure. Future clinical trials evaluating its many clinical applications will help to define populations of patients most apt to benefit from this type of treatment.