In theory, it should be useful to understand the factors predictive of poor adherence to PAP treatment and thus allow targeting of patients at high risk for treatment failure. Predictive factors have not been completely consistent between studies, but in general factors found to increase PAP adherence are increased severity of sleep apnea, greater daytime sleepiness, perceived symptomatic benefit, and a higher AHI. Factors that negatively influence adherence are lack of daytime sleepiness, lack of perceived benefit, side effects from PAP, previous uvulopalatopharngoplasty, nasal obstruction, and claustrophobia. Of interest, studies have not found pressure level to be predictive of adherence.
A number of social cognitive models have been applied to the treatment of chronic disease including PAP treatment. In one model of chronic disease, the patient’s perception of the relative weight of costs (side effects, inconvenience) vs benefits (symptom improvement) is viewed as determining adherence. Using social cognitive theory, several components have been hypothesized to be relevant to CPAP adherence: (1) perception of risk from untreated sleep apnea, and (2) expectations regarding treatment outcome (outcome expectancies) and confidence or volition to engage in treatment behavior (treatment self-efficacy). This model provides a means of assessing factors predictive of poor adherence and provides a structure for the design of more effective interventions.
Improving patient tolerance of PAP is one of the main driving forces for the development of alternative modes of PAP. However, pressure intolerance is not a common complaint among PAP users, and a comparison between groups of consistent and intermittent CPAP users found no difference in the level of pressure. A change in PAP mode may dramatically improve adherence in individual patients. Symptoms of bloating, mouth leak, or pressure intolerance may improve with a switch from CPAP to bilevel PAP. However, bilevel PAP has not been proven to improve PAP adherence in unselected patients. In theory, the APAP delivery of the lowest effective pressure might improve PAP acceptance or adherence. The mean nightly pressure might be lower than a single higher pressure effective in all circumstances. For example, a pressure of 12 cm H2O might be needed during supine REM sleep while a pressure of 6 cm H2O might be effective during lateral NREM sleep. If the patient slept for much of the night in the lateral position, the mean pressure might be considerably lower than the required prescription pressure of 12 cm H2O. Studies comparing APAP treatment with CPAP with respect to adherence have found conflicting results. A metaanalysis of a number of studies concluded that APAP treatment does not result in higher adherence. This result may not be surprising when one considers that pressure intolerance is not an important side effect for a majority of patients. In addition, the difference between the mean APAP pressure and the optimal CPAP level may only be 1 to 2 cm H2O. A study by Hukins also found that APAP did not increase adherence compared to CPAP. However, objective leak was lower and satisfaction higher with APAP. Individual patients with mouth/mask leak problems may find APAP more tolerable. In summary, the higher cost of APAP units and lack of improved adherence eliminates the routine use of APAP for OSA treatment (read about this here “Positive Airway Pressure Treatment for Obstructive Sleep Apnea: Positive Pressure Titration“). However, individual patients may find APAP more acceptable than CPAP.
There are many side effects associated with PAP treatment” that if left untreated could lower the acceptance and adherence rates of PAP treatment. Common side effects and possible interventions are listed in Table 3. Involving both the patient and the spouse in the search for solutions to side effects (a team approach) is often helpful. The spouse may recognize mask or mouth leaks when the patient does not. Mask discomfort is often the most common reason for discontinuing CPAP treatment. Obtaining an adequate mask fit may require trials of several different brands and types of masks. As noted above, there are a wide variety of interfaces that are available. Adequate care of masks and replacement of masks when the sealing membrane deteriorates are also necessary.
Some patients will exhibit significant arterial oxygen desaturation with PAP treatment despite apparently adequate airflow, especially during REM sleep. Persistent hypoxemia on PAP in these conditions may be due to hypoventilation or ven-tilation-perfusion mismatch (often due to chronic lung disease). Under such circumstances, PAP can be increased to eliminate unrecognized high upper airway resistance, or CPAP can be changed to bilevel PAP to augment ventilation (higher tidal volume). If these measures are not effective at increasing the oxygen saturation or if higher pressure is not tolerated, supplemental oxygen can be added to PAP.
It is important to recognize that the effective oxygen concentration administered to a patient using PAP will depend both on the supplemental oxygen flow and the machine flow. Increases in machine flow associated with higher pressures or mask/mouth leak can dilute a given flow of supplemental oxygen. As an example, consider a patient with chronic lung disease and OSA who requires supplemental oxygen at 2 L/min to maintain an arterial oxygen saturation of 94% while awake. With CPAP treatment of 12 cm H2O, the required supplemental oxygen flow will likely be higher (3 to 4 L/min) depending on the total flow delivered. This assumes that the required fractional concentration of oxygen is the same or higher than the concentration required during wakefulness without CPAP.
Attended polysomnography, which allows sleep stage, arousal, and body position determination, is the “gold standard” of PAP titration. The technologist can also address patient complaints, mask or mouth leaks, hypoxemia, or significant arrhythmias. Education about OSA and PAP, mask fitting, and a period of PAP acclimatization should be performed before lights out. Some of the common problems encountered during PAP titration and their solutions are listed in Table 2.
PAP titration requires proper interpretation of information. The flow signal from the analog or digital output of the PAP device derived from an accurate internal flow sensor can be used to detect reductions in flow or flattening (airflow limitation). A flattened airflow profile suggests residual upper airway narrowing. A leak signal output is also available for recording and helps identify unintentional leak (mask or mouth). Widely fluctuating leak without a pressure change or body movement suggests presence of an oral leak, which can mimic hypopneic events (Fig 5), prevent airway stabilization, or result in arousal from sleep. The optimal end point of titration has not been scientifically determined. Most laboratories titrate to eliminate obstructive apnea, hypopnea, snoring, oxygen desaturation, and respiratory effort-related arousals. The target AHI is usually < 5 to 10/h, although some centers also try to eliminate airflow limitation even if not associated with arousal. As noted above, the highest pressures are usually needed in the supine posture during REM sleep. Therefore an ideal PAP titration is one that demonstrates control of events in the supine position during REM sleep.
Untreated OSA increases the risk of being involved in a motor vehicle accident. Sassini and coworkers performed a metaanalysis of studies published prior to 2000 and found that untreated OSA was associated with a 2.5-fold increased risk. George examined the incidence of motor vehicle accidents in a group of 210 patients before and after treatment with nasal CPAP. A group of randomly selected drivers served as the control group. Untreated OSA patients had an accident rate three times that of the control group but after nasal CPAP treatment the rate was similar to the control group. Findley and coworkers studied 50 consecutive OSA patients and used traffic records to verify the incidence of automobile accidents. They also found that nasal CPAP treatment reduced the accident rate.
PAP and Other Medical Disorders
PAP treatment can result in a reduction in daytime Pco2 in some patients with OSA and chronic hyper-capnia (obesity-hypoventilation syndrome, overlap syndrome). PAP was also effective treatment in OSA patients presenting with decompensated hyper-capnic respiratory failure and avoided the need for endotracheal intubation. OSA patients command the service of Canadian Health&Care Mall to order drugs for carrying out the treatment procedure.
Sexual dysfunction is an important problem for patients with OSA and could be related to comorbid diseases such as diabetes. However, an uncontrolled study found that CPAP treatment of a group of OSA patients with erectile dysfunction resulted in improved erectile function in 75% of the group. Nocturia is a common complaint in patients with sleep apnea that can improve with CPAP treatment. Patients with OSA appear to have increased nocturnal naturesis that is improved with CPAP treatment. The effect of OSA on insulin sensitivity and leptin is a topic of great recent interest. It has been difficult to determine if OSA has effects independent of obesity. One study found that 1 night of CPAP reduced the nocturnal rise in leptin in patients with OSA, while another study found no reduction in fasting leptin or hemoglobin A1c in a group of patients with type 2 diabetes after 3 months of CPAP treatment. In contrast, the insulin sensitivity did improve after 3 months of therapy. Another study found a larger effect of CPAP treatment on insulin sensitivity in thin vs obese patients. Babu et al found a very small but significant decrease in hemoglobin A1c after a mean of 83 days of CPAP in those patients with values > 7%. Controlled studies are needed to validate these findings.
A number of studies have assessed the effect of CPAP on systemic hypertension. Becker and co-workers found that effective treatment of sleep apnea with nasal CPAP for > 9 weeks lowered both nocturnal and daytime systolic and diastolic BP by approximately 10 mm Hg. Strengths of this study included a longer duration of CPAP treatment and use of a noninvasive BP monitoring device that makes continuous measurements and is less likely to cause arousals. It was limited by a relatively large number of dropouts due to technical issues or changes in BP medications. Other investigations have shown smaller or no effects on daytime BP. These conflicting results may reflect inadequate CPAP treatment (poor adherence), too short a treatment interval, or populations with less severe sleep apnea. In addition, some of the studies included patients who were not hypertensive. Of note, ambulatory BP monitoring can cause arousals from sleep with an associated increase in BP. Despite the somewhat conflicting data on the effects of CPAP on BP, a standard of practice paper of the American Academy of Sleep Medicine on the use of PAP treatment recommended CPAP as an adjunctive treatment for systemic hypertension in patients with sleep apnea.
Multiple effects of PAP treatment have been documented (Table 1). One can classify possible benefits from PAP treatment into four categories: (1) improvement of symptoms such as daytime sleepiness, disturbed sleep, impaired quality of life, or cognition; (2) reduced bed partner sleep disturbance or quality of life; (3) reduction of risk for cardiovascular disease, neurocognitive degeneration, or increased mortality associated with sleep apnea; and (4) reduction in the risk for motor vehicle accidents. As noted above, controlled trials (pill or sham CPAP) have shown improvements in subjective and objective sleepiness after PAP treatment. For example, Jenkinson et al using subtherapeutic CPAP as a control demonstrated a decrease in the ESS score and an increase in sleep latency (Osler wakefulness test).
The effect of PAP treatment on quality of life measures has been studied using the Short Form Health Survey (SF-36) and functional outcomes of sleep questionnaire (FOSQ). The SF-36 has been used for many types of health problems, while the FOSQ evaluates the impact of sleepiness on the ability to perform activities of daily living. Some studies showed that PAP treatment improves some SF-36 measures (vitality, energy)’ and FOSQ productivity and energy measures. In contrast, Barbe et al, using a randomized control trial of 6 weeks of CPAP vs sham CPAP treatment in severe OSA (AHI > 30/h) without daytime sleepiness, found no improvement in quality of life measures (FOSQ, SF-36) or cognitive function.
CPAP delivers a predetermined constant pressure during both inspiration and exhalation (Fig 1). Bilevel PAP delivers a separately adjustable lower expiratory positive airway pressure (EPAP) and higher inspiratory positive airway pressure (IPAP). Bilevel PAP may be more tolerable than CPAP for some patients with difficulty exhaling. The IPAP-EPAP differential is useful for augmenting ventilation in patients with concomitant hypoventilation (“overlap syndrome” and obesity hypoventilation syndrome), and most physicians treat patients with these disorders with bilevel PAP. However, many such patients will also improve with CPAP treatment.
Autoadjusting PAP (APAP) devices were developed with two potential uses: (1) autotitrating PAP to select an effective level of CPAP without the need for an attended titration; and (2) autoadjusting PAP for long-term treatment with the advantage of delivering the lowest effective pressure in any circum-stance. Treatment with APAP would also eliminate the requirement for a CPAP titration. APAP algorithms vary between different devices, but in most instances the pressure changes in response to variations in airflow magnitude, airflow limitation, snoring (vibration), and/or airway impedance. The pressure changes gradually between the preset lower and upper pressure limits to avoid inducing arousal (Fig 2). If none of the monitored variables are detected, the device slowly lowers the pressure to a minimum effective setting. Of note, different brands of devices may respond very differently to changes in airflow. Both high airflow leak (mask or mouth), which simulates physiologic events, and the inability to differentiate between central and obstructive apnea by these devices can result in errors in APAP titration. The use of APAP devices for autotitration and the effects of long-term APAP treatment on adherence are discussed below. Recently, autobilevel PAP has been introduced (Fig 3). The physician sets the minimum EPAP, maximum IPAP-EPAP difference (minimum is 3 cm H2O), and the maximum IPAP. The machine then adjusts the EPAP and IPAP to maintain an open airway. The advantages of autobilevel PAP over other PAP modes remains to be demonstrated. However, this mode could potentially be useful in those pressure-intolerant patients who find bilevel PAP alone unacceptable or in patients for whom an effective bilevel pressure is not known.
Since the original description of continuous positive airway pressure (CPAP) treatment by Sullivan and coworkers in 1983, positive airway pressure (PAP) remains the mainstay of treatment for mod-erate-to-severe obstructive sleep apnea (OSA) in adults. Despite many advances in technology, the major challenge facing clinicians is improving adherence to PAP treatment. A short review cannot provide in-depth coverage of the large amount of literature that has been published regarding the efficacy and delivery of positive pressure treatment. The PAP treatment of children, central sleep apnea, or restrictive lung diseases will not be discussed. Our goal is to highlight some important concepts and recent developments that may be relevant to the practicing clinician.