Redefining successful therapy in obstructive sleep apnea: A call to arms

Obstructive sleep apnea (OSA) is a common illness affecting 9% of middle-aged men and 3% of middle-aged women in North America. The current diagnostic methods for OSA include in-laboratory polysomnography (PSG) and home portable monitoring, both which report the apnea– hypopnea index (AHI) as the primary metric of OSA severity. Furthermore, the effectiveness of surgical treatments for OSA is almost exclusively on reported changes in AHI. However, recent evidence has shown that there is a disconnect between the levels of AHI used to denote outcomes of therapy and real world clinical outcomes such as QOL (quality of life), physical findings, patient perception of disease, and/or survival. Moreover, in many areas of medicine and for all manner of diseases, patient-centered outcome measures and QOL assessments are gaining substantial traction as priority items to assess when gauging the effect of therapy. In the case of OSA, however, the AHI remains paradoxically persistent as the main—and frequently the only—outcome measure reported in the vast majority of surgical and nonsurgical OSA studies in the literature. QOL, daytime sleepiness, personal performance, and various physiological measurements have been proposed as markers for OSA but have not been widely adopted. In this editorial, we propose that the evidence base now exists to modernize the concept of what defines success in surgery for sleep apnea. From a patient’s perspective, AHI is a nebulous concept, whereas other outcomes measures are of more impactful relevance—including subjective sleepiness, snoring level, and level of performance. In addition, OSA treatment aims to prevent the long-term deleterious effects of the disease (e.g., high blood pressure and cardiovascular morbidity), yet such assessments are notably underutilized and relatively invisible in both medical and surgical studies evaluating treatment outcomes. Even when AHI is used, the interpretation of outcome can still be unclear. In the surgical literature, the widely cited Sher success criteria of 50% reduction in AHI and an AHI< 20 are considered the benchmark. However this long-held concept is based on historical literature that did not even stratify patients by likelihood of surgical success; thus, it is now outdated and should be abandoned. For example, a patient with a baseline AHI of 75 who had a postoperative PSG showing an AHI of 30 would likely experience measurable symptomatic clinical improvement with a huge decrease in disease burden (in terms of decreased obesity, decreased sleepiness, improved hypertension, and cardiovascular effects), even though the patient is not defined as a successful surgical outcome by the numerical Sher criteria. However, a patient with a baseline AHI of 35 that is reduced postoperatively to 14 is considered a successful AHI outcome even though the likelihood of clinical cardiovascular or QOL impact may be minimal. Hobson et al. recently showed in a creative study that even differences in the definition of AHI severity cutoff can greatly influence the reported efficacy of surgery in patients with OSA. With regard to the CPAP literature, the majority of the published articles focus on the in-lab AHI reduction, which does not take into account the critical issue of patient adherence and resulting total-sleep-time AHI, thus consistently overemphasizing the success of CPAP therapy. For example, if we again look at a patient with an AHI of 75, the patient would need to use the CPAP for a total sleep time of over 90% to reduce the AHI to less than 10. This amount of use would not be typical in a CPAP population. To even achieve the Sherdefined success point of an AHI of 20, the patient would need to use the CPAP machine over 85% of sleep time, which falls well beyond the American Academy of Sleep Medicine’s defined minimum usage of 70% of night for 4 hours per night. Until recently, the issue of total-sleeptime CPAP use and its effect on posttreatment AHI has been severely understated in the CPAP literature. Employing AHI as the single variable with which to gauge the success of therapy—either medical or surgical— allows it to hold too much weight in the field of sleep medicine. Other metrics of OSA measurement such as QOL, subjective sleepiness, performance, and biological measures must evolve to play a larger role to study outcomes. Validated subjective measurements such as QOL scores, sleepiness scores, and performance testing better reflect the patient experience than does AHI. Objective measures such as blood pressure more directly measure important longterm goals that OSA interventions aim to treat than does AHI. We recognize the existence of data linking AHI to cardiovascular risk status via various landmark studies (e.g., Wisconsin Sleep Cohort and Sleep Heart Health Study). Our intent is not to specifically minimize the importance of AHI, but rather to emphasize the need to report other measures to better capture the patient OSA experience. This editorial is a call to arms for clinicians involved in the treatment of OSA. OSA is more than just