Noninvasive positive pressure ventilation for stable outpatients: CPAP and beyond
ABSTRACTNoninvasive positive pressure ventilation (NIPPV) has been used in outpatients with sleep apnea, sleep disorders associated with heart failure, restrictive pulmonary diseases (subsuming neuromuscular diseases and thoracic cage deformities), severe stable chronic obstructive pulmonary disease, and the obesity-hypoventilation syndrome. NIPPV in these settings has resulted in significant physiologic benefits, improved quality of life, and in some cases longer survival. We discuss the modes of NIPPV, current indications, and potential benefits.
KEY POINTS
- In sleep apnea, NIPPV has both short-term benefits such as improved daytime alertness and reduced fatigue, and long-term benefits such as a reduced cardiovascular risk.
- The potential development of complex sleep apnea with NIPPV may be managed by using lower pressures, by continued treatment (more than half of cases improve over time), and by advanced options such as adaptive servo-ventilation.
- In patients with concomitant obstructive sleep apnea and congestive heart failure, NIPPV, particularly bilevel positive airway pressure, improves blood pressure and left ventricular function, though it is not clear whether it has a survival benefit.
Obesity-hypoventilation syndrome
Obesity-hypoventilation syndrome refers to daytime hypercapnia (Paco2 > 45 mm Hg) in obese people when no other cause of hypoventilation is present.
The prevalence of obesity-hypoventilation syndrome among patients with obstructive sleep apnea-hypopnea syndrome is 20% to 30% and is greater in extremely obese patients (body mass index > 40 kg/m2).64 However, about 10% of patients with obesity-hypoventilation syndrome do not have obstructive sleep apnea-hypopnea syndrome.64 Additionally, nocturnal hypoxemia and diurnal hypercapnia persist in about 40% of patients with obesity-hypoventilation syndrome after CPAP eliminates their sleep apnea.65 Therefore, factors other than sleep apnea contribute to the development of obesity-hypoventilation syndrome, and in a meta-analysis, factors associated with daytime hypercapnia included, in addition to body mass index and the apnea-hypopnea index, mean overnight oxygen saturation and severity of restrictive pulmonary function.66 Predictors of success with CPAP include better spirometric findings, a higher apnea-hypopnea index, and adequate oxygenation.67,68
Bilevel PAP therapy can be tried in patients in whom CPAP by itself fails. In a study of patients with obesity-hypoventilation syndrome in whom initial CPAP treatment failed, average volume-assured pressure support lowered Paco2 compared to bilevel PAP alone, but did not further improve oxygenation, sleep quality, or quality of life.69
Restrictive pulmonary diseases
Neuromuscular diseases and thoracic cage abnormalities. Noninvasive ventilation has been used in patients with progressive neuromuscular disorders or severe thoracic cage abnormalities, with recognized benefits including an improved survival rate and improved quality of life.70,71 However, NIPPV is used in only 9% of patients with amyotrophic lateral sclerosis when clearly indicated.72 The indications and Medicare guidelines for reimbursement of NIPPV (with or without a backup rate) in this setting are shown in Table 2.
Potential contraindications to starting NIPPV in this population include upper airway obstruction, failure to clear secretions despite optimal noninvasive support, inability to achieve a mask fit, and intolerance of the intervention.73,74
The mechanisms of benefit of NIPPV in these settings include improvements in daytime blood gas levels (including hypercapnia75), a reduction in the oxygen cost of breathing,76 an increase in the ventilatory response to carbon dioxide,75 and improved lung compliance.77
Chronic hypercapnic failure due to severe COPD
The use of NIPPV in chronic COPD is less well established than in patients with exacerbations of COPD,78 and limitations in its use are reflected in the more stringent Medicare indications for NIPPV in this setting (Table 2).
A particular subset of patients with stable COPD who may benefit from NIPPV includes those with daytime hypercapnia and super-imposed nocturnal hypoventilation.78 The potential benefits of NIPPV in these patients include improved daytime and nocturnal gas exchange, increased sleep duration, and improved quality of life.78 Additionally, a recent randomized controlled trial of NIPPV plus long-term oxygen therapy compared with oxygen therapy alone in patients with severe COPD and a Paco2 greater than 46 mm Hg demonstrated a survival benefit in favor of adding NIPPV (hazard ratio 0.6).79
However, that study also found no reduction in hospitalization rates, an apparent worsening in general and mental health (as reflected on the 36-Item Short Form Health Survey or SF-36, a quality-of-life questionnaire), as well as increased confusion and bewilderment (reflected on the Profile of Mood States scale).79 These potentially deleterious effects may explain why adherence to NIPPV is low in patients with stable COPD: only 37% to 57% of patients continued to use it in several reported studies.79–81
A level of inspiratory pressure support that is insufficient to reduce hypercapnia may account for the low adherence rate and worsened quality of life in such patients. For instance, in a randomized trial,82 compared with low-intensity NIPPV (mean IPAP 14 cm H2O, backup rate 8 per minute), settings that aimed to maximally reduce Paco2 (mean IPAP 29 cm H2O with a backup rate of 17.5 per minute) increased the daily use of NIPPV by 3.6 hours/day and improved exercise-related dyspnea, daytime Paco2, forced expiratory volume in 1 second (FEV1), vital capacity, and health-related quality of life.
The overlap syndrome was first described by Flenley in 1985 as a combination of chronic respiratory disease (more generally limited to COPD) and obstructive sleep apnea-hypopnea syndrome.83 Epidemiologic studies do not consistently show a higher incidence of obstructive sleep apnea-hypopnea syndrome in patients with COPD, but the exaggerated oxygen desaturation during sleep in patients with this combination increases the risk of hypoxemia, hypercapnia, and pulmonary hypertension. 84 In addition, there was evidence of higher risks of death and of hospitalization for COPD in patients with the overlap syndrome. 85 NIPPV is the main treatment for obstructive sleep apnea-hypopnea syndrome with or without COPD.
A recent study by Marin et al85 showed that CPAP was associated with improved survival and decreased hospitalization in patients with the overlap syndrome. However, polysomnography or nocturnal oximetry while on NIPPV alone must be done, as additional nocturnal oxygen therapy may be warranted when significant chronic respiratory illness coexists with sleep apnea.
Acknowledgment: The authors gratefully acknowledge the contribution of Scott Marlow, RRT, to Table 2 of this review.
