Key points

Background

Positive airway pressure (PAP) has been used to treat obstructive sleep apnea syndrome (OSAS) for more than 30 years. PAP prevents upper airway collapse: it functions as a pneumatic splint, increasing the caliber of the upper airway and it also increases lung volumes, which provides tracheal traction. PAP is considered first-line therapy for moderate to severe obstructive sleep apnea and may also be considered for mild obstructive sleep apnea, particularly if it is symptomatic or there are concomitant cardiovascular disorders. The indications for PAP include apnea hypopnea index (AHI) or respiratory disturbance index greater than or equal to 15 events per hour or AHI or respiratory disturbance index between 5 and 14 events per hour associated with symptoms such as excessive daytime sleepiness, impaired neurocognitive function, mood disorders, insomnia or cardiovascular disease (eg, hypertension, ischemic heart disease, congestive heart failure, atrial fibrillation) or history of stroke. The use of PAP for OSAS improves respiratory disturbances, daytime sleepiness, cognitive impairment, mood, and quality of life ; reduces automobile accidents ; and improves cardiovascular sequela, such as systemic hypertension. Treatment of OSAS with PAP is optimized by using a multidisciplinary approach including a sleep specialist, the referring physician, nurses, respiratory therapists, and the sleep technologist.

Background

Positive airway pressure (PAP) has been used to treat obstructive sleep apnea syndrome (OSAS) for more than 30 years. PAP prevents upper airway collapse: it functions as a pneumatic splint, increasing the caliber of the upper airway and it also increases lung volumes, which provides tracheal traction. PAP is considered first-line therapy for moderate to severe obstructive sleep apnea and may also be considered for mild obstructive sleep apnea, particularly if it is symptomatic or there are concomitant cardiovascular disorders. The indications for PAP include apnea hypopnea index (AHI) or respiratory disturbance index greater than or equal to 15 events per hour or AHI or respiratory disturbance index between 5 and 14 events per hour associated with symptoms such as excessive daytime sleepiness, impaired neurocognitive function, mood disorders, insomnia or cardiovascular disease (eg, hypertension, ischemic heart disease, congestive heart failure, atrial fibrillation) or history of stroke. The use of PAP for OSAS improves respiratory disturbances, daytime sleepiness, cognitive impairment, mood, and quality of life ; reduces automobile accidents ; and improves cardiovascular sequela, such as systemic hypertension. Treatment of OSAS with PAP is optimized by using a multidisciplinary approach including a sleep specialist, the referring physician, nurses, respiratory therapists, and the sleep technologist.

Positive airway pressure delivery systems

PAP devices are air pumps (fan-driven or turbine systems) that draw in external, filtered air to deliver pressured airflow. The airflow is adjusted by changing the diameter of the pressure valve or turbine/fan speed. Over the years, PAP machines have become more quiet, compact, and portable.

PAP is delivered by a variety of interfaces: nasal, oronasal, and oral (ie, nasal mask, nasal pillows, oronasal [face] mask, oral mask, and oral mask with nasal pillows). The choice of optimal interface is important, because it may influence a patient’s acceptance of PAP therapy and long-term compliance. The most commonly used interfaces are the face and nasal masks. Nasal pillows and oral masks may be considered as alternatives if a patient cannot tolerate the nasal or face masks. Face masks may be considered when nasal obstruction or mouth breathing limit the effectiveness of the nasal mask or greater inspired relative humidity is desired. Masks have been developed by manufacturers to maximize patient comfort, using softer cushions.

Most currently available PAP devices include digital software that keeps track of date and time of usage, and detects and measures apnea, hypopnea (AHI), snore, flow limitation, periodic breathing, air leaks and flow waveform. In essence, these devices can measure many of the respiratory parameters that are monitored during a polysomnogram (PSG). Without the extensive monitoring of the PSG, it is not possible to determine the sleep stage of the patient or to accurately assess some of the physiologic complications of the OSAS. However, devices have advanced to the point that they can use the measured respiratory parameters to provide feedback in a closed-loop system and to manipulate the output variables.

Modes of positive airway pressure

Many of the modes of PAP used for OSAS have variations of pressure-support or pressure-controlled ventilation. A target pressure is set and the resultant tidal volumes depend on the level of inspiratory pressure, respiratory system compliance, airway (upper and lower) resistance, and tubing resistance. Tidal volumes increase with increases in the inspiratory pressure and respiratory compliance and decreases in airway and device tubing resistance. In contrast, tidal volumes decrease with decreases in inspiratory pressure and respiratory compliance and increases in airway or device tubing resistance.

Continuous positive airway pressure

Continuous PAP (CPAP) is the initial and most commonly used modality for OSAS. It refers to the delivery of a continuous level of PAP, which is similar to positive end-expiratory pressure. The patient initiates all breaths; no additional pressure is given to support the individual breaths. The optimal setting for PAP titration is determined in an accredited sleep center or laboratory during a titration study, or obtained by examining data from an autotitrating device. It is important for all PAP candidates to receive adequate education, hands-on demonstration, careful mask fitting, and acclimatization before the titration. The goal of titration is to eliminate obstructive-related events, such as apneas, hypopneas, respiratory effort-related arousals, and snoring. The recommended minimum starting CPAP is 4 cm H ₂ O, although higher levels are used in patients with obesity or for retitration studies. The maximum CPAP usually is 15 cm H ₂ O for children and 20 cm H ₂ O for patients greater than or equal to 12 years. CPAP is increased in a stepwise fashion by at least 1 cm H ₂ O if obstructive events are seen. Once the optimal CPAP is obtained, then a downtitration may be performed.

Goals of the PAP titration study are a respiratory disturbance index (total of apneas, hypopneas, and respiratory effort-related arousals) less than 5 per hour, sea level oxygen saturation as measured by pulse oximetry greater than 90%, and an acceptable air leak around the mask. In addition, the airflow tracing should be normalized and snoring should be eliminated. Optimal titrations include elimination of obstructive events during supine rapid eye movement sleep without producing arousals or awakenings. The full-night PSG is the optimal approach for titration; however, for some adults split-night titration studies may be adequate. The effectiveness of split-night studies for titration of CPAP in children less than or equal to 12 years has not been adequately studied.

Bilevel positive airway pressure

Bilevel PAP (BPAP) without a backup rate is indicated for patients with OSAS who do not respond to or are intolerant of CPAP. BPAP with a backup rate is indicated for patients with OSAS and respiratory insufficiency with hypoventilation caused by restrictive lung disease (ie, thoracic insufficiency, neuromuscular disease), obesity hypoventilation syndrome, central apnea and obstructive lung disease, such as chronic obstructive pulmonary disease (COPD).

BPAP is effective in improving gas exchange in patients with obstructive and restrictive lung disease. In patients with OSAS who do not have coexisting daytime respiratory disease, BPAP may be used when CPAP is inadequate or not tolerated by the patient. It is not usually used as first-line therapy, because the device that delivers BPAP is more expensive than the CPAP machine. BPAP delivers a preset inspiratory PAP (IPAP) and expiratory PAP (EPAP). The tidal volume depends on the difference between the IPAP and the EPAP (delta P). Increases in the delta P usually increase minute ventilation and can improve alveolar ventilation. The device coordinates the breath with the patient’s inspiratory effort; the pressure-supported breath is triggered by a change in the patient’s inspiratory air flow or airway pressure. In BPAP, a backup rate can be set if the patient is at risk for central apnea. The recommended starting pressures for IPAP and EPAP are 8 H ₂ O and 4 cm H ₂ O, respectively. The recommended maximum IPAP is 20 cm H ₂ O for children and 30 cm H ₂ O for patients greater than or equal to 12 years old. The minimum delta P is usually set at 4 cm H ₂ O and the maximum at 10 cm H ₂ O. Of note, the abbreviation “BiPAP” is often used interchangeably with BPAP. However, BiPAP is a proprietary term that refers to BPAP delivered with a specific company’s device (Philips Respironics).

The potential advantages of BPAP when compared with CPAP include active ventilation (rather than just pneumatic splinting), decreased mean airway pressure (which could lead to better tolerance of the therapy), less respiratory muscle fatigue, and faster resolution of respiratory acidosis. There are few studies that compare the effectiveness of BPAP with CPAP in OSAS in either adults or children. In adults with obesity hypoventilation, one study found that BPAP was no better than CPAP as measured by gas exchange, sleepiness, or adherence, but it was associated with better sleep quality and psychomotor vigilance performance. However, in most other studies in adults and children without coexisting daytime respiratory disease, BPAP offered no advantage over CPAP in either efficacy or adherence when used as initial treatment. There are some data to support that it is an effective alternative in patients who are intolerant of or nonadherent to CPAP. One potential disadvantage of BPAP is patient-device asynchrony, which can lead to discomfort and ineffective ventilation.

Autotitrating positive airway pressure

Autotitrating mode PAP (APAP) is indicated for patients with OSAS, and patients with OSAS nonresponsive or intolerant of fixed PAP. CPAP and BPAP may be used in an auto-titrating mode, which uses feedback from the patient’s respiratory monitoring to automatically adjust airway pressures. Its potential advantages include using it for initial titration of airway pressures in place of PSG in a sleep laboratory and to decrease the mean airway pressure, which could improve patient compliance. For autotitrating CPAP, an airway pressure is set. If there are greater than a preset number of obstructive events (for example two events in a 3-minute period), the pressure is automatically increased in a stepwise fashion to a predetermined maximum. Once the obstructive episodes have been eliminated, then a downtitration is performed. APAP devices in the self-adjusting mode may be used for home studies to initiate treatment and to determine the optimal pressure for patients with OSAS who do not have significant comorbidities (eg, congestive heart failure, COPD, central sleep apnea syndromes, or hypoventilation syndromes). The use of autotitrating CPAP has been associated with small improvements in adherence and sleepiness when compared with fixed CPAP, the clinical significance of which remains unclear. However, autotitrating CPAP may actually be less effective than fixed CPAP at reducing the cardiovascular sequela associated with OSAS because it may cause more sympathetic activation.

Autotitrating BPAP works in a similar manner. Preset inspiratory and expiratory pressures are used. If the patient has a critical number of obstructive events, then the pressures automatically increase in a stepwise fashion. In some algorithms, if an obstructive apnea occurs, EPAP increases and if an obstructive hypopnea occurs, then IPAP increases. To maintain adequate minute ventilation, a minimum delta P (ie 4 cm H ₂ O) is set. In one study, autotitrating BPAP further improved ventilation and obstructive events in patients who were intolerant or unresponsive to CPAP ; however, it is unclear whether the improvement was caused by the BPAP or the autotitrating mode.

Comfort features

Variations in the pattern of airflow during PAP, such as pressure relief modes and ramps, have been developed to improve patient comfort and adherence. A pressure relief mode was developed for CPAP and BPAP, because inspiration and exhalation against high pressures can produce dyspnea. In this mode, gradual, instead of abrupt, changes are used to deliver airway pressure. For example, in pressure relief mode with CPAP, a small decrease in airway pressure accompanies the beginning of exhalation. Additional modifications soften the pressure transition from inhalation to exhalation. In BPAP with pressure relief, there is a decrease in airway pressure at the beginning of exhalation and softening of the pressure transition from inhalation to exhalation and exhalation to inhalation. Studies have not consistently demonstrated that pressure relief when added to CPAP improves adherence or patient outcomes. BPAP with pressure relief was associated with better compliance than CPAP alone in patients previous noncompliant with CPAP ; however, it is unclear whether the improvement was caused by the pressure relief or BPAP. Device manufacturers have developed devices that are tailored for female patients; they include unique APAP algorithms and gender-specific masks. Another comfort feature is a ramp that is used with patients who require a more gradual increase in PAP. In this method, there is a slow, stepwise increase to target pressures in the beginning of the cycle (ie, for 0–45 minutes). Some devices may be set to shorten this ramp period if they detect obstructive events. Use of the ramp has not been demonstrated to improve patient adherence.