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Note: Patient 2 had a high residual AHI.

Abbreviations: AI, apnea index; HI, hypopnea index; AHI, apnea-hypopnea index.

Note: Patient 2 had a high residual AHI.

Abbreviations: AI, apnea index; HI, hypopnea index; AHI, apnea-hypopnea index.

FIGURE 7 Effects of auto-positive airway pressure (APAP) versus continuous positive airway pressure (CPAP) on adherence. A positive score indicated a better adherence to APAP than CPAP. The X axis is the nightly adherence with APAP minus adherence with CPAP. Y axis: studies reporting adherence ordered by publication year. The bottom diamond represents the pooled effect, with the dashed line drawn though the mean of this estimate. The composite data are consistent with no increase in adherence on APAP versus CPAP treatment. Source: From Ref. 33.

FIGURE 7 Effects of auto-positive airway pressure (APAP) versus continuous positive airway pressure (CPAP) on adherence. A positive score indicated a better adherence to APAP than CPAP. The X axis is the nightly adherence with APAP minus adherence with CPAP. Y axis: studies reporting adherence ordered by publication year. The bottom diamond represents the pooled effect, with the dashed line drawn though the mean of this estimate. The composite data are consistent with no increase in adherence on APAP versus CPAP treatment. Source: From Ref. 33.

et al. (32) concluded that there was no significant increase in adherence with APAP treatment compared to fixed CPAP in these studies. In evaluating studies of adherence several issues must be considered. First, pressure intolerance is not the major issue for many patients (34). Second, the difference in the mean pressure on APAP and an adequate fixed pressure is oft en only 1 to 2 cm (30) H2O (Fig. 8). One would not expect such a small pressure difference to change adherence.

FIGURE 8 The number of patients with displayed differences between the manual effective continuous positive airway pressure (Pman) and the mean nightly pressure on auto-positive airway pressure (APAP). While a few patients had a much lower mean pressure on APAP compared to the fixed pressure (Pman), the difference was only 1 or 2 cm H2O in most patients. Source: From Ref. 30.

FIGURE 8 The number of patients with displayed differences between the manual effective continuous positive airway pressure (Pman) and the mean nightly pressure on auto-positive airway pressure (APAP). While a few patients had a much lower mean pressure on APAP compared to the fixed pressure (Pman), the difference was only 1 or 2 cm H2O in most patients. Source: From Ref. 30.

Are there subsets of OSA patients who would adhere better to APAP than fixed CPAP? One might expect a potential advantage for APAP devices in patients with pressure intolerance, high prescription pressures, or a large variation in the required pressure during the night (postural or REM-related OSA) (35). However, Noseda et al. (36) found no evidence for increased adherence in patients with a high variability in pressure requirement. A major problem with this study is that it did not target pressure intolerant patients. Of interest, Hukins (32) found evidence of lower leak and fewer reported side effects on APAP compared to fixed CPAP treatment. Lowering the mean pressure might be expected to minimize mask leak or the tendency for mouth leak. Leak, especially mouth leak, often results in dryness that may not respond to the addition of heated humidity (37-39). Thus, chronic APAP treatment provides a useful alternative in patients with a mask or mouth leak problem that does not respond to interventions such as a change in mask type or size or an increase in the delivered humidity.

Although APAP treatment appears to have no advantage over CPAP with respect to adherence in unselected patients, several studies have demonstrated a patient preference for APAP (30,32,40). It would be useful to be able to predict which patients might prefer treatment with APAP. Marrone et al. (40) compared APAP and fixed CPAP treatment using a crossover design. Of 22 patients, 14 preferred APAP treatment. However, analysis of group characteristics found no factor that would predict a preference for APAP. Of interest is the finding that only those patients with a preference for APAP had higher adherence to APAP than CPAP. Thus, if a patient is having difficulty with CPAP, a trial of APAP is a reasonable intervention. If APAP is preferred, improved adherence is likely with this mode of treatment compared to fixed CPAP. Furthermore, information stored in the machine such as leak or residual events may help diagnose problems with treatment.

Patients with difficulty tolerating CPAP due to pressure intolerance ("cannot breathe out") are often switched to BPAP. One study compared intervention with APAP to that with BPAP in patients with difficult-to-treat sleep apnea (41). The inclusion criteria were patients requiring CPAP > 12 cm H2O, those not tolerating CPAP, and those with central apneas that worsened on CPAP. Both APAP and BPAP improved subjective sleepiness with equivalent adherence. A majority of the patients preferred APAP at the end of the study. As APAP devices are considerably less expensive than BPAP devices, this study suggests that a trial of APAP treatment should be given consideration when CPAP is not well-tolerated.

Although the fact that APAP treatment does not improve adherence over fixed CPAP selected by manual titration, the equivalence of these treatments suggests another role for APAP devices. That is, patients diagnosed with OSA could be treated with chronic APAP without the need for either traditional laboratory titration or auto-titration. Any additional cost of APAP devices over CPAP would usually be less than the cost of an in-laboratory CPAP titration. In fact, one study (31) found both a cost saving and a reduction in the time needed to adjust the PAP treatment to a satisfactory level. Indeed it is a common experience that the optimal level of CPAP determined by an attended in-laboratory titration often requires alteration for patient tolerance, side effects, or control of daytime sleepiness.

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