Pros and Cons of Using Apnea-Hypopnea Index as an Index for Assessing Postoperative Outcomes in Sleep Apnea

Obstructive sleep apnea (OSA) is a commom disorder characterized by repetitive partial or complete cessation of airflow, causing intermittent hypoxia during sleep.OSA is associated with various comorbidities and complications and requires treatment.Currently, the three main treatment options are sleep surgery, positive airway pressure (PAP) therapy, and oral appliance.While continuous PAP (CPAP), introduced as a treatment for OSA by Sullivan et al. [1] in 1981, is considered as the standard treatment, uvulopalopharyngoplasty (UPPP), the most renowned surgical treatment, was first introduced by Ikematsu [2] in the early 1960s, published in English by Fujita et al. [3] in the early 1980s, and has been widely used.Since its introduction, various surgeries have been developed and the efficacy of sleep surgery has significantly improved with the introduction of multi-level surgeries.However, the success rate of sleep surgery remains moderate.A recent systematic review of sleep surgery based on the Apnea-Hypopnea Index (AHI) demonstrated significant variability [4].Elshaug et al. [5] suggest redefining the success rate of airway surgery for OSA because the AHI levels used in surgical success criteria are higher than those for CPAP.Applying the same AHI criteria to both CPAP and sleep surgeries could lead to a perceived lower success rate for upper airway (UA) surgery, potentially making them less favorable.Nevertheless, numerous studies have confirmed the efficacy of surgical treatments for OSA.A multicenter, prospective, longitudinal study showed that UPPP significantly improves disease-specific quality of life and sleep apnea symptoms in OSA patients [6].Another study comparing CPAP to sleep surgery in veterans with sleep apnea found that UPPP had a higher survival rate than CPAP (96.6% vs. 92.9%)after adjusting for age, gender, race, year of treatment, and comorbidity [7].One reason for these differing outcomes could be the definition of CPAP compliance, usually accepted as using CPAP for with a minimum 4 hours of PAP usage per night for 70% of the nights.Using a mathematical function formula, Ravesloot and de Vries [8] demonstrated that the greater the severity of OSA, the more the use of CPAP is required to significantly reduce the AHI less than 5 or 10.They proposed that the mean AHI during CPAP therapy might be a more realistic index, and arbitrary compliance criteria might conceal insufficient reductions in AHI.Consider a patient with an AHI of 60/hour who sleeps for 8 hours per night for 30% of nights in a week and use CPAP, achieving an AHI of 5, for merely 4 hours per night for 70% of nights in a week (AHI=32.5/night).Despite an average AHI of 40.35/hour across all nights of a week, this patient would still be classified as "compliant" according to the current compliance definition.For a patient who underwent sleep surgery, with a postoperative AHI of 24 and a sleep duration of 8 hours per night, the average AHI across all nights of a week would be 24.Since developed by C. Guilleminault and W. Dement, AHI has been a dominant index for sleep apnea and used across nearly every field of sleep medicine.However, AHI essentially quantifies the number of episodes of apnea and hypopnea per