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Subscribe to Clinical Compass™ VOLUME 2, ISSUE 14 - JULY 3, 2007

FROM THE CLINICAL KNOWLEDGE CENTER
Does Nightly Duration of CPAP Affect Treatment Response?

by Michelle Ostrander, PhD

Our previous issue of Clinical Compass™ reviewed the prevalence, consequences, and current management options for obstructive sleep apnea (OSA)—a sleep related breathing disorder characterized by complete or partial obstruction of the airway that results in symptoms such as loud snoring, severely fragmented sleep, and excessive sleepiness, among others. Current management options for this potentially serious disorder range from lifestyle modifications, oral appliances,* continuous positive airway pressure (CPAP), and surgical interventions, depending on severity of the condition and refractoriness to treatment.

Although CPAP is widely considered the most efficacious treatment for OSA, its effectiveness for patients may be limited by variability in nightly use of the treatment. Given that optimal effectiveness of CPAP depends on consistent use, it is of considerable clinical importance to determine the impact of differential use of CPAP on measurable outcomes of sleepiness and functional status. A recent paper published by Weaver et al. in the journal Sleep, as well as reader feedback on our previous article, has prompted us to more closely consider this issue.

Weaver and colleagues sought to determine the estimated likelihoods of return to normal levels of sleepiness and daily functioning relative to nightly duration of CPAP usage. Study participants included 149 individuals (130 men, 19 women; age 19 to 65 years) attending one of seven sleep disorder centers in the United States or Canada who were diagnosed with severe OSA (apnea-hypopnea index [AHI] ≥ 15). Participants completed 2 days of testing – 1 day prior to CPAP treatment and another day 3 months after initiation of treatment. Testing on these occasions included a demographics questionnaire, the Epworth Sleepiness Scale (ESS), the Multiple Sleep Latency Test (MSLT), and the Functional Outcomes of Sleep Questionnaire (FOSQ). The ESS measured subjective sleepiness, the MSLT assessed objective sleepiness, and the FOSQ measured functional status, a component of quality of life. Following the initial day of testing, subjects then underwent either a full-night, diagnostic polysomnogram followed by a CPAP titration polysomnogram or a split-night study in which a diagnosis of OSA was made during the first half of the night and CPAP titration was conducted during the second half of the night.

Participants were included in the analysis for each outcome (ESS, MSLT, FOSQ) only if complete pretreatment and post-treatment data were available, and if they had abnormal scores at baseline. Scores were considered abnormal for an outcome if they met the following conditions: ESS > 10, MSLT < 7.5 min, and FOSQ < 17.9. Conducting the statistical analysis in this manner prevented a possible “ceiling effect” which may have occurred as a result of including individuals with normal baseline values.

Of individuals for whom a complete set of pretreatment and post-treatment data were available on an individual assessment (ESS, n = 137; MLST, n = 136; FOSQ, n = 147), 77% reported excessive subjective sleepiness (ESS > 10), 63% exhibited objective sleepiness (MSLT < 7.5 min), and 82% had sleep-related functional impairment (FOSQ < 17.9). Mean hours of CPAP use were significantly different between individuals with normalized ESS scores (responders, 5.1 ± 2.1 hours per night) compared to CPAP use in individuals with abnormal ESS scores (non-responders, 4.0 ± 2.3 hours per night, p = .02). Similarly, the number of mean hours of CPAP use per night was significantly different for responders versus non-responders on the MSLT (5.1 ± 1.7 vs. 3.9 ± 2.4, p = .01) and the FOSQ (5.1 ± 1.9 vs. 4.1 ± 2.3, p = .01). However, response to treatment on the outcome measures (ESS, MSLT, FOSQ) was not dependent on pretreatment scores.

The percentage of patients with abnormal pretreatment values who achieved normal post-treatment values after 3 months of CPAP use was determined for each assessment. For the ESS, 41% of patients attained a normal ESS score with ≤ 2 hours of CPAP use per night whereas 93% of patients had a normal ESS score with ≥ 7 hours of CPAP use per night. For the MSLT, 13% of participants had a normal MSLT score with ≤ 2 hours of CPAP use per night whereas 43% of participants achieved a normal MSLT score with ≥ 5 hours of CPAP use per night. For the FOSQ, 33% of patients with ≤ 2 hours of CPAP per night attained a normal FOSQ score whereas 68% of patients had a normal FOSQ score with ≥ 5 hours of CPAP use per night. Further analyses determined thresholds in CPAP use that were not expected to yield further substantial improvements in scores on the ESS (4 hours), MSLT (6 hours), and FOSQ (7.5 hours). In addition, regression analyses indicated a linear dose-response relationship for mean hours of CPAP use per night for performance on the ESS and the MSLT (p < .0001 and p = .005, respectively). Taken together, these data suggest that a greater percentage of patients with pretreatment impairments will attain improvements in subjective and objective measures of sleepiness, as well as normalization of functional outcomes, with longer use of CPAP on a nightly basis. However, the length of adequate use varies depending on the outcome.

The authors note some limitations to this study including the lack of a control group, the specification of impairment on the MSLT as 7.5 min, and the lack of objective data on sleep duration prior to testing. Despite these limitations, the results of this study provide important messages regarding the effectiveness of CPAP treatment in clinical practice. First, from a population perspective, longer use of CPAP is associated with greater improvements in sleepiness, although this may vary at the level of the individual. Second, there is a subset of patients who can achieve normalized function with limited CPAP use. Thus, the actual need for CPAP to reverse sleepiness varies on an individual basis and treatment effectiveness should be determined by adherence level in combination with outcome measures.

* In February 2006 the American Academy of Sleep Medicine published practice guidelines stating that oral appliances are indicated for patients with mild to moderate sleep apnea who prefer their use to CPAP, as well as for patients who are inappropriate candidates for or are refractory to CPAP treatment.

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References

  • Weaver TE, Maislin G, Dinges DF, et al. Relationship between hours of CPAP use and achieving normal levels of sleepiness and daily functioning. Sleep 2007;30:711-719.



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