Adherence See Also Chapter 9 General Issues

It is widely acknowledged that CPAP is an effective treatment for OSA but just as readily recognized that there are significant limitations to patients' effective use of this treatment modality. In addition to adherence, various other terms such as compliance, acceptance, and others have been used by authors when reporting studies describing utilization of prescribed CPAP treatment. These terms need standardized definitions and use to allow valid across-studies interpretation of results (85). True "efficacy" studies have yet to be performed. Such studies would need to measure not only the CPAP usage and residual "breakthrough" respiratory events, but also the total amount of sleep. Thus, a measure of not only protected sleep (as measured on the CPAP device), but also the amount of "unprotected" sleep, without CPAP therapy. Nevertheless, when one looks at all the CPAP usage data currently available, adherence with CPAP devices compares favorably with medication use in various other chronic medical conditions.

Several specific factors can potentially affect CPAP initial acceptance and long-term adherence, including machine cost, the technical characteristics of the equipment, and prescriber motivation. Current machines are quieter compared to those of past years, with a ramp facility to slowly increase the pressure over the first period of sleep, and there are more comfortable masks. Many earlier CPAP usage studies used equipment that has been replaced by newer devices (for example, the "C-Flex" CPAP device; see above section: Pressure Level and Airflow) and adherence data need to be continually updated to verify whether these technical changes do actually influence CPAP use or are purely "cosmetic" in the intense marketing environment of CPAP equipment sales. This situation is somewhat analogous to clinical trials of new medications within the same drug class, for example, comparative studies of beta-blockers.

Most contemporary CPAP equipment includes some mechanism for adherence monitoring. Many feature the ability to detect ventilation, and record "mask-on-face" time. If a CPAP mask is taken off the face, there is detectable drop in pressure and loss of the predictable ventilatory pattern. This can be recorded on devices with data storage capability. So, if patients simply switch on their machine and leave the mask on the floor, then there would be a major discrepancy between "machine-on" time and "mask-on-face" time. A simultaneous study of CPAP use and pressure delivery at the mask revealed a reasonable correlation between claimed usage and measured adherence (86).

"Dosage" studies are not available for CPAP. The question do patients have to use CPAP every night to receive beneficial therapeutic effects? remains incompletely answered. Even average CPAP use of less than four hours per night produces a demonstrable reduction in sleepiness (87). Another study showed that one night off CPAP in adherent CPAP users led to a recurrence in daytime sleepiness (88). At this stage all criteria set for CPAP usage or nonusage or adherence or nonadherence (86,87) are essentially arbitrary. Newer studies are anticipated that may help define these criteria according to meaningful physiologic or neurocognitive outcomes.

Furthermore, it is clear that even partial-night CPAP use can lead to measurable clinical improvement. Some sleep apnea patients use CPAP for only part of the night because they derive a satisfactory degree of symptomatic benefit from that limited application (81). This possibly reflects interindividual variation of function with sleep loss or fragmentation, with some patients "needing" to obtain less sleep to function at a reasonable level during wakefulness (82). Given the evidence that shortened sleep hours are associated with significant performance deficit, patients need to be warned about the risk of persisting problems with alertness, which may accompany limited hours of use of CPAP. Newer-generation CPAP devices that allow monitoring of more precise patterns of use and efficacy will give us insight into the minimal duration of CPAP use that is needed to maintain normal daytime neurobehavioral function and, possibly, to modify the vascular consequences of sleep apnea.

Sleep Apnea

Sleep Apnea

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