Apnea Calculator

Rationale

Obstructive sleep apnea (OSA) is the most prevalent sleep disordered breathing problem, affecting 2-26% of the general population, depending on gender, age, and definition of the used criteria 1 2. OSA is associated with significant morbidity, such as excessive daytime sleepiness, social unacceptable snoring, increased risk of cardiovascular disease and mortality and impaired quality of life3.

Various methods exist to treat OSA. The gold standard is continuous positive airway pressure (CPAP) therapy., which is regarded as successful if the AHI drops below 5, when CPAP is used. Unfortunately, it is a clinical reality that the use of CPAP is often cumbersome and that CPAP compliance rates are poor.

Approximately 15-30% patients refuse CPAP, patients are often discouraged by the aesthetic aspect or the thought of being bound to CPAP for the rest of their lives4. In patients who are willing to try CPAP, pressure is titrated to reduce the individual patient’s AHI to less than 5 events per hour5. Most patients who discontinue CPAP treatment, do so after a few months. In spite of advances in CPAP technology, such as auto-PAP, Bilevel-PAP, heated humidification, a large range of interfaces and mask comfort improvement as well as educational and behavioral support, patient adherence has only marginally improved in the last 23 years.5 6 7 8 9 Approximately 20-40% will discontinue CPAP after 3 months7.

Surgery, on the other hand, is slowly gaining momentum, due to improvements in patient selection, through use of the Friedman classification system, by means of drug-induced sleep endoscopy and by applying more site specific surgical techniques compared to earlier days, when the only surgical technique available was UPPP. Nevertheless, the Sher surgical success criteria are difficult to fulfill, especially in cases with severe or extreme OSA. It is generally easier to reach surgical success in patients with a low AHI, which is somewhat unjust. For example, a reduction of a mere 15 is needed to reach Sher’s criteria in a patient with an initial AHI of 30, whilst a far larger decrease would be necessary in a patient with an AHI of 80, and CPAP failure. A reduction of 60 points would be insufficient (mandatory) to qualify for success, even though it goes without saying that the gain in quality of life and reduction of cardiovascular risk is likely to be more outspoken in comparison to the less serious cases with a reduction of only 19 points.

The current notions of surgical success are overdue for reevaluation, but we contend the same holds true for CPAP33 10.

CPAP compliance rates vary greatly. Weaver and Grunstein report in their review that 29-83% of patients are non adherent and use their CPAP less than 4 hours per night8. We recently analyzed the compliance of 232 CPAP users5. Only 138 (59.5%) of these 232 patients were “compliant”, with compliant liberally defined as CPAP use >4hrs/night, >5 days /week. Even in this compliant group, the mean CPAP use was 6.5 hrs/night (81% with a given 8hrs/night, SD 1.5), and 6.4 nights/week (91%, SD 1.4). With a CPAP use of 81% per night and 91% night/week, compliant patients on average still only use the device 74% of the TST5. Patients seem to either tolerate the device well or not at all; a bimodal distribution11.

Self evident, even the most effective medical devices are only effective when they are used. The effect may be 100% when always used, nil when never used and partial when used sometimes but not always. This is particulary true for CPAP use in OSA. Therefore, using a mean AHI in CPAP therapy is more realistic than using arbitrary compliance rates, which in fact hide insufficient reductions in AHI.

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11 Weaver TE, Kribbs NB, Pack AI et al. Night-to-night variability in CPAP use over first three months of treatment. Sleep 1997;20:278-83.