INTRODUCTION
Sleep apnea is a condition in which breathing temporarily stops or decreases during sleep. This condition is divided into obstructive, central, and mixed types, with obstructive sleep apnea (OSA) being the most common type, accounting for over 80% of cases [
1]. OSA is characterized by repetitive periods of breathing cessation lasting for ≥10 sec despite repeated efforts to breathe [
2]. Apneas and hypopneas are terminated by temporary awakenings, leading to excessive daytime sleepiness and fatigue. OSA is often reported by patients who experience choking or gasping sensations during sleep or by their bed partners who witness snoring and apnea episodes [
3]. The prevalence of OSA in South Korea is reported to be 4.5% in males and 3.2% in females [
4]; however, the actual prevalence is estimated to be approximately 20%–30% in middle-aged individuals, as many cases are undiagnosed due to unawareness of the symptoms [
4]. OSA is considered an independent risk factor for various chronic diseases, including metabolic disorders [
5] and cardiovascular conditions such as hypertension, congestive heart failure, coronary artery disease, and stroke [
6]. Additionally, OSA causes neurological and mood disorders such as depression and cognitive impairments [
7,
8].
In cases of suspected OSA due to clinical symptoms and signs, a polysomnography study is necessary for the final diagnosis [
9]. The treatment of choice for moderate-to-severe OSA involves the use of positive airway pressure (PAP) devices. The PAP device delivers continuous air pressure to the airway to keep it open and promote unobstructed breathing. Numerous studies have suggested that successful treatment is possible in >80% of patients with OSA [
9]; however, long-term compliance can be a hurdle. When compliance is defined as using the device for a minimum of 4 hours a day, at least 5 days a week, international studies have reported that 30%–80% of patients were compliant. Studies in South Korea before National Health Insurance (NHI) coverage was implemented showed that approximately 40% of patients were compliant [
10-
12]. After insurance coverage, compliance was 84.8% over 3 months after coverage [
13].
Low compliance can result from factors including frequent awakenings in patients with OSA and insomnia due to the PAP mask preventing sleep, machine noise disrupting sleep, and bulky device size. Other factors contributing to low compliance include skin damage, inflammation, pain caused by wearing a mask, and anxiety or discomfort associated with device usage [
14]. In the past, PAP therapy was hindered by high costs; however, since July 2018, it has been covered by the NHI for patients with OSA who were diagnosed using polysomnography, making it more accessible. In South Korea, insurance coverage for PAP treatment is provided and maintained based on patient compliance. Compliance is assessed every 3 months after the initial period, and if the patient does not submit usage records or if the average usage is less than 2 hours a day, insurance coverage is discontinued [
13].
In Korea’s clinical setting, several studies have been conducted to investigate changes in device compliance among patients with OSA following the introduction of NHI coverage for PAP devices. Some of these studies reported an increase in PAP compliance at the third- and sixth-month follow-ups, while others found higher compliance rates in the first and third months but no statistically significant differences in the ninth month [
10,
13]. Additionally, a study reported that even after initiating insurance coverage, 87.9% of patients discontinued PAP therapy within 13 months, and 51.7% of those who discontinued it before 13 months cited device maladaptation as the reason [
15]. These findings suggest that while insurance coverage may impact the initial and short-term compliance increase with PAP treatment, other factors need to be considered for long-term compliance, and identifying factors that hinder PAP device usage early on is crucial.
In South Korea, residents are required to enroll in the NHI system and pay insurance premiums. Among them, beneficiaries of medical aid are individuals with income below a certain level who receive medical services provided by the NHI without paying premiums. As an exception, national merit recipients do not enroll in the NHI but instead receive medical services from veterans’ hospitals and contracted hospitals (
Figure 1) [
16].
The Veterans Health Service Medical Center (VHS Medical Center) provides an environment conducive to studying the relationship between NHI coverage and PAP compliance because it has a significant number of patients who are not members of the NHI and receive medical benefits in comparison with those in university hospitals. This study aimed to evaluate short-term PAP adherence in patients who underwent polysomnography and were diagnosed with OSA with an apneahypopnea index (AHI) score >15 at the VHS Medical Center and to identify NHI enrollment or medical aid and other related factors affecting PAP adherence.
DISCUSSION
This study showed that patients who were enrolled in the NHI recorded significantly higher 3-month PAP adherence than that in patients without NHI after considering factors such as insomnia, depression, age, years of education, duration of oxygen desaturation, presence of DEB, and BMI. Moreover, patients who benefited from medical aid did not have a higher 3-month PAP adherence than that in patients with medical insurance.
The 3-month PAP adherence rate among the study participants was 45.8%. This result is significantly lower than the 84.8% adherence rate reported in another 3-month study conducted at a tertiary hospital [
13]. Before the NHI-covered PAP treatment, one institution reported a 6-month adherence rate of 35.7% [
22] and another reported a 41.5% adherence rate [
11], however, this was based on a different time frame than the 3-month period in this study, making direct comparisons challenging. Several factors can influence PAP therapy adherence, including patient-, physician-, and device-related factors [
23]. This study’s more detailed examination focused on cost burden on the patient, age, and psychological factors. Specifically, some potential reasons for the relatively low PAP adherence observed in this study include the following: a unique patient population of the hospital where the research was conducted, as it primarily serves national merit recipients and their families; a high proportion of older patients; the operation of a sleep clinic within the department of psychiatry that may have influenced the patient population and their adherence; and the high prevalence of trauma histories in patients that led to the observation of DEB.
The cost of renting a PAP device may be a barrier or facilitator of adherence. Before the NHI started covering PAP treatment in South Korea, monthly rental fees varied by the company but were generally approximately 200,000–300,000 KRW (approximately 150–225 US dollars). After NHI coverage, monthly rental fees were approximately 34 US dollars before the adherence period and 13–15 US dollars after. As of June 2018, research findings suggest that this change in rental fees led to increased PAP adherence [
13].
However, the VHS Medical Center, where this study was conducted, primarily serves national merit recipients, such as veterans and their family members, and has a population of patients who are not enrolled in the NHI. This factor has been shown to have a significant impact on PAP adherence. South Korea has implemented the NHI system for the entire nation, covering nearly 99% of the population. However, national merit recipients such as veterans and their family members have the option to choose whether to enroll in the NHI or opt out according to Article 5, Paragraph 1 of the NHI Act [
16]. Individuals who opt out of the NHI or do not have health insurance can receive medical benefits at the VHS Medical Center and affiliated hospitals. In such cases, family members can benefit from the reduced medical fees when seeking treatment at the VHS Medical Center. In this study, 42 out of 579 patients (7%) were not enrolled in the NHI, which differs from the 1% rate on not-enrollment in the NHI among the entire population. Consequently, the high number of patients without an NHI at VHS Medical Center has led to different rates of PAP device application based on health insurance status. Even among health insurance enrollees, many patients may not pay any or most of their medical expenses, as they qualify for reduced or waived fees. This is particularly relevant for PAP device rental, where some patients may find the burden of costs unfair. In the clinical setting, it has been observed that some patients become upset when a doctor recommends PAP device rental after undergoing polysomnography because they are required to bear the cost. Some patients may expect to rent the device for free, leading them to consider changing hospitals to pursue such benefits.
Meanwhile, as a public hospital, the VHS Medical Center often receives medical aid beneficiary patients regardless of whether they are national merit recipients or not. Patients benefiting from medical aid can use PAP devices without incurring personal costs. Economically, patients receiving medical aid are expected to have significantly higher PAP adherence. However, the results of this study showed that the presence of medical aid did not have a statistically significant effect on PAP adherence. It was challenging to emphasize that NHI support simply increases compliance because compliance did not increase for medical aid beneficiaries who can rent the machine for free. For patients receiving medical aid, it seems like economic factors do not act as luring factor since they don’t need to pay personal cost regardless of adherence. This suggests that not only economic factors, but also various factors, including age, years of education, insomnia, and depression, may collectively influence adherence rates.
In this study, the average age of both groups was >65 years, indicating an older population compared to that in a previous study [
13]. Individuals aged ≥65 years are often retired from stable employment and may rely on low or no work-related income, depending on pension income for their livelihood. This demographic group may experience economic concerns related to the rental cost of PAP devices.
In this study, the group meeting the PAP adherence criteria was younger than the nonadherent group, suggesting that age can impact PAP compliance. Previous research from the USA reported varying adherence rates based on age groups; the percentage of individuals meeting the PAP adherence criteria increased significantly from 54.7% in the age group of 18–30 years to 79.0% in the 61–70 years age group and then slightly decreased to 73.1% in the 81–90 years age group [
24]. These results show that the age group with the highest PAP adherence rate was not necessarily the youngest, indicating that PAP adherence is influenced by multiple factors beyond age. In a similar study conducted in South Korea, the “good adherence” group tended to be younger than the “poor adherence” group; however, statistically significant differences were not observed [
13]. These results regarding adherence vary according to age and sex, which could be influenced by differences in each country’s insurance and older adults’ welfare systems or cultural norms [
25].
Furthermore, as this study was conducted on patients visiting a sleep clinic within the department of psychiatry, there may be a higher distribution of individuals with insomnia than that in studies conducted in another department, such as otolaryngology. Individuals who failed to meet the PAP adherence criteria had a higher prevalence of insomnia and higher BDI-II scores than those of individuals who met the adherence criteria. This likely reflects the significant impact of a patient’s low-arousal threshold [
26] and hyperarousal state on PAP adherence [
27]. A low arousal threshold in patients with OSA refers to the tendency to wake up easily in response to a relatively mild airway obstruction during sleep. This condition is one of the physiological characteristics that occurs in over one-third of patients with OSA and can result in difficulty maintaining sleep, leading to insomnia [
26]. Additionally, individuals with insomnia and depression may exhibit overactivation of the arousal system, possibly due to psychophysiological hyperarousal caused by increased orexin, which plays a role in both the arousal and affective systems [
27].
In this study, when comparing the results of polysomnography between the PAP-adherent and nonadherent groups, the PAP-adherent group had a higher AHI, a longer duration of SaO
2<90, and a lower occurrence of DEB. Previous studies have shown no strong association between PAP adherence and AHI severity or nocturnal hypoxemia [
13,
23]. However, another study showed that good adherence groups tended to have higher AHI and significantly higher non-rapid eye movement sleep and supine AHI [
13]. The need for PAP may be emphasized in patients with higher AHI severity or nocturnal hypoxemia. The observation that individuals with DEB were less likely to achieve good adherence could be related to the presence of idiopathic REM RBDs and trauma-related sleep disorders [
28]. Some patients may exhibit body movements or vocalizations during sleep due to conditions such as combat trauma or military trauma-related sleep disorders, making the use of PAP therapy challenging.
Furthermore, the study found that individuals who achieved PAP adherence had more years of education than those who did not. This suggests that a patient’s understanding of the necessity of PAP therapy may influence adherence. Doctors often need to explain the importance of PAP therapy to patients with OSA within a limited time frame, and some patients may find it difficult to comprehend. Therefore, research has suggested that both face-to-face and e-health interventions can extend the duration of PAP use, emphasizing the importance of patient education and support in improving adherence [
29].
This study had some limitations. First, due to the characteristics of the VHS Medical Center where the study was conducted, there was an unequal sex distribution (93.8% males) and a high proportion of patients over the age of 65 years, making it difficult to represent the entire patient population. Second, the study defined the PAP-adherent group as individuals who used PAP therapy for a minimum of 4 hours a day for more than 21 days out of 30 consecutive days within the first 90 days of receiving the prescription, which allows for an assessment of short-term adherence only. As previous research has shown that adherence can change depending on the duration of follow-up, future studies should consider analyzing the factors affecting long-term adherence based on the results of this study. Also, it was challenging to find prior research in South Korea comparing compliance rates between medical aid and medical insurance. This difficulty may stem from the rarity of medical aid beneficiaries visiting hospitals engaged in research and article publication, making it hard to secure research participants. In addition, to assess psychiatric conditions, the study used information such as BDI-II and the use of antidepressant medications; hence, the actual diagnosis of mood or anxiety disorders was not confirmed. Furthermore, because the study was retrospective, we could only rely on information recorded by the authors. Finally, it is worth noting that the study did not consider findings related to structural abnormalities of the nose, such as nasal septum deviation, or factors such as the Mallampati score, that reflect the upper airway structure. Additionally, medical conditions such as rhinitis or asthma, which can potentially influence PAP adherence, were not considered in this study. These factors can also affect the patient’s ability to adhere to PAP therapy and could be important for a more comprehensive understanding of the topic.
Despite these limitations, this study is valuable in its ability to identify patient characteristics associated with difficulties in PAP adherence. It would be good for clinicians to consider these factors and use them as a reference to increase compliance.