CPAP can produce objective and subjective improvements in patients with OSA and other types of SDB (21-23). Despite its demonstrable efficacy, many OSA patients have difficulty with long-term acceptance of CPAP (24,25). Several intervention strategies have been suggested to improve adherence to CPAP, including use of specialized education and follow-up programs (26,27) and added airway humidification (28). Others have suggested that modifications of the airflow delivery pattern, as with continuously auto-adjusting CPAP (29) or bilevel devices capable of varying inspiratory and expiratory levels (9), may also boost adherence in more difficult-to-treat OSA patients.

As these earlier reports indicated, there was a general reduction in the mean effective PAP level using BPAP compared to CPAP (3,9). It was therefore thought that bilevel devices might prove to be a benefit for improvement in adherence to PAP in OSA patients. There have been two high-level evidence randomized trials that compared the use of BPAP versus CPAP for OSA patients who were first time users without complicating comorbid medical problems. The first study randomized 83 OSA patients to receive either CPAP or BPAP with a primary endpoint of adherence based on mean machine timer hours of CPAP (30). A total of 62 patients were evaluated and followed for one year and of these, 26 received BPAP and 36 CPAP pressures. The groups did not differ for BPAP versus CPAP by age (48 ± 1 years vs. 46 ± 1 years) or BMI (40 ± 1 kg/m2 vs. 39 ± 1 kg/m2), but were different by gender (65.5% vs. 52.8% males). Over the 12-month period, the mean machine timer hours of CPAP versus bilevel therapy were not different at 5.0 ± 0.19 (SEM) versus 4.9 ± 0.23 hours per night. There was also no difference between high and low hourly users for the CPAP or BPAP pressures required during therapy. These patients had similar percentages of time that the machine was running at the prescribed effective pressure at 80% in the CPAP group and 82% in the BPAP users with both groups reporting an equal number of complaints with respect to mask discomfort, machine noise, and nasal stuffiness.

The second high-level evidence trial studied newly diagnosed OSA patients without coexisting daytime respiratory disease and compared CPAP with a bilevel device that also employed a prototype flow feature of the presently available Bi-Flex® device (Respironics, Inc., Murrysville, Pennsylvania, U.S.) (31). The primary endpoint was the percentage of nights with at least four hours of use and hours of use per night after 30 days treatment. This was based on objective machine-determined measurement of time at effective pressure beginning after diagnosis and titration by split-night polysomnography (PSG) in a sleep laboratory. There were no significant baseline group differences for the 27 adults (22 men) in age, BMI, AHI (mean ± SD, CPAP vs. BPAP group of 46.1 ± 23.1 events/hour vs. 41.8 ± 25.8 events/hour, respectively), CPAP requirement, or scores on the Epworth sleepiness scale and Functional Outcomes of Sleep Questionnaire. The percentage of nights with > 4 hours/night use was high in both groups but was not significantly different (CPAP vs. BPAP = 80.5 ± 24% vs. 77.6 ± 24.8%). In both of these studies, the BPAP appeared to be as effective as CPAP for the treatment of OSA but offered no advantages in patients receiving first-time therapy for OSA.

A randomized controlled trial published in 2005 investigated whether BPAP with Bi-Flex could prove valuable in patients who were considered nonadherent to CPAP therapy (32). The unique design had two phases that first attempted to improve adherence to a treatment threshold of four hours per night of CPAP. There were 204 adult patients diagnosed with OSA (AHI > 10) by PSG within 24 months who had been titrated to an optimal CPAP level but were not able to adhere to regular CPAP use (nonresponders) at a mean treatment time of 254 ± 333 (SD) days. Patients were questioned about various complaints and these were addressed with a systematic conventional intervention program including further education, CPAP desensitization as needed, alternative mask or resizing, and heated humidification. After two more weeks of CPAP therapy there were 24% (49 patients) who became responders (> 4 hours/night), 76% (155 patients) who were still nonresponders or who withdrew. The nonresponders who agreed to proceed on to phase 2 then had a full-night PSG retitration and blinded randomization to either CPAP or Bi-Flex for three months. In the 104 patients initiating the trial, there were no significant differences in baseline characteristics of the Bi-Flex versus CPAP groups for age (51.9 ± 11.3 years vs. 52.5 ± 11.3 years), sex (65% vs. 72% males), BMI (33.4 ± 7.9 kg/m2 vs. 32.5 ± 6.3 kg/m2), and AHI (40.4 ± 23.4 events/hour vs. 44.0 ± 26.1 events/hour). At three months, there was a trend to a higher success rate with Bi-Flex versus CPAP treatment (49% vs. 28.3% of patients using PAP therapy > 4 hours/night; p < 0.05) but the overall success rate for either PAP treatment was low at near 40%. The authors found no strong clinical predictors to distinguish patients in either arm who become adherent (responders) after conventional intervention techniques and concluded that sleep specialists must be very aggressive at achieving initial CPAP adherence as subsequent efforts to achieve optimal adherence to PAP therapy are less fruitful but consideration could be given to repeat PSG and use of alternative modes of flow delivery to further encourage patients to use PAP treatment.

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