Noninvasive positive pressure ventilation (NIPPV) is any form of positive ventilatory support applied without an endotracheal tube, including continuous positive airway pressure (CPAP).1 The role of NIPPV in acute care has been discussed in an earlier review in the Cleveland Clinic Journal of Medicine.2
NIPPV is also used at night in outpatients with stable chronic conditions, first used in the 1980s in the treatment of obstructive sleep apnea3 and neuromuscular diseases,4 and since then in several other conditions including sleep disorders associated with congestive heart failure (including sleep apnea and the Cheyne-Stokes respiration-central sleep apnea syndrome), chronic obstructive pulmonary disease (COPD), and the obesity-hypoventilation syndrome.
In this review, we discuss the different types of NIPPV, the specific conditions in which they can be used, and the indications, recommendations, and evidence supporting the efficacy of NIPPV in outpatients.
THE TYPES OF NIPPV AND THEIR USES
Although the conditions for which different types of NIPPV can be used overlap significantly, each type has general indications and different goals of treatment. This section begins with types of NIPPV that are predominantly used to treat sleep-disordered breathing, and then proceeds to those predominantly used for conditions associated with hypoventilation and hypercapnia.
Continuous positive airway pressure
CPAP, currently the most widely used form of NIPPV, applies a constant level of positive pressure at the airway opening during spontaneous breathing.
CPAP is commonly used to treat obstructive sleep-disordered breathing, with the goals of improving daytime sleepiness and reducing cardiovascular risk. It has also been used to treat sleep-disordered breathing associated with congestive heart failure.
CPAP’s role in the support of ventilation is limited and indirect. For instance, it has been used in the obesity-hypoventilation syndrome and in the “overlap” syndrome (in which both sleep apnea and COPD coexist). However, its benefits in those conditions are probably derived in large part from correction of underlying obstructive sleep apnea.
The mechanisms of action of CPAP include:
- Preventing intermittent narrowing and collapse of the airway in patients with obstructive sleep apnea-hypopnea syndrome by acting as a pneumatic splint during sleep3,5,6
- Counteracting auto-positive end-expiratory pressure, thereby reducing respiratory muscle load, reducing the work of breathing, and lowering daytime Paco2 in patients with coexistent COPD and obstructive sleep apnea-hypopnea syndrome (the overlap syndrome)7–9
- Improving lung function (particularly the functional residual capacity) and daytime gas exchange in obstructive sleep apnea-hypopnea syndrome 10
- Improving left ventricular systolic function in patients with heart failure coexisting with obstructive sleep apnea-hypopnea syndrome.11,12
Auto-CPAP is delivered via a self-titrating CPAP device, which uses algorithms to detect variations in the degree of obstruction and consequently adjusts the pressure level to restore normal breathing. Auto-CPAP therefore compensates for factors that modify the upper airway collapsibility, such as body posture during sleep, stage of sleep, use of alcohol, and drugs that affect upper airway muscle tone.13
Although one of the premises of using auto-CPAP is that it improves the patient’s satisfaction and compliance, several studies found it to be no more effective than fixed CPAP for treating obstructive sleep apnea-hypopnea syndrome.14–16 Current guidelines of the American Academy of Sleep Medicine do not recommend self-titrating CPAP devices to diagnose obstructive sleep apnea or to treat patients with cardiopulmonary disorders or other conditions in which nocturnal desaturation may be unrelated to obstructive events.17
Adaptive servo-ventilation was developed for Cheyne-Stokes respiration-central sleep apnea syndrome in patients with congestive heart failure, who may have periods of crescendo-decrescendo change in tidal volume (Cheyne-Stokes respiration) with possible intercalated episodes of central apnea or hypopnea. It is also applied in patients with the complex sleep apnea syndrome.
Adaptive servo-ventilation devices are usually set at an expiratory positive airway pressure (EPAP) level sufficient to control obstructive sleep apnea. The device then automatically adjusts the pressure support for each inspiration, within a prespecified range, to maintain a moving-target ventilation set at 90% of the patient’s recent average ventilation. The aim is to stabilize breathing and reduce respiratory alkalosis, which can trigger apnea reentry cycles.18
Bilevel positive airway pressure
Bilevel positive airway pressure (bilevel PAP) can be of use in sleep-disordered breathing (including cases associated with congestive heart failure), but it is predominantly applied in conditions associated with hypoventilation.
Bilevel PAP devices deliver a higher pressure during inspiration (inspiratory positive airway pressure, or IPAP) and a lower pressure during expiration (EPAP). The gradient between IPAP and EPAP is of key importance in maintaining alveolar ventilation and reducing Paco2. The IPAP acts as pressure support to augment the patient’s effort, maintain adequate alveolar ventilation, unload respiratory muscles, decrease the work of breathing, and control obstructive hypopnea, whereas EPAP is set to maintain upper airway patency, control obstructive apnea, improve functional residual capacity, and prevent microatelectasis.
Although there is no evidence that bilevel PAP is better adhered to or more effective than CPAP, current guidelines propose it as an option for patients who require high pressures to control obstructive sleep apnea-hypopnea syndrome or for those who cannot tolerate exhaling against a high fixed CPAP pressure.19
Other, more-common uses of bilevel PAP are to treat coexisting central sleep apnea or hypoventilation,19 the obesity-hypoventilation syndrome with residual alveolar hypoventilation despite CPAP and control of concomitant obstructive sleep apnea-hypopnea syndrome,5,20 severe stable COPD with significant nocturnal hypoventilation and daytime hypercarbia,21 and restrictive pulmonary diseases.21