Chronic hypoxemia is a major complication of advanced chronic respiratory diseases, such as chronic obstructive lung disease (COPD), interstitial lung disease (ILD), and lung cancer. Chronic hypoxemia is associated with decreased quality of life, exercise capacity, and increased mortality [1,2]. Long-term oxygen therapy (LTOT) has been recommended by international guidelines for decades at these stages of chronic lung disease [3,4].

Using LTOT for at least 15 hr/day improves survival in patients with chronic resting hypoxemia. Evidence of LTOT based on a randomized controlled trials in the early 1980s, the Medical Research Council (MRC) study, revealed a higher survival rate of 5 years after randomization in severely hypoxemic patients with COPD receiving supplemental oxygen therapy (OT) for >15 hr/day compared to the survival of those without OT [5]. In clinical practice, LTOT is commonly prescribed for other diseases such as ILD, cor pulmonale, cardiac disease, or neuromuscular disease using the same criteria used for COPD [6,7].

National and international guidelines recommend LTOT in the presence of appropriate criteria, which are defined as a resting partial pressure of oxygen in arterial blood (PaO₂) of 55 mm Hg or oxygen saturation (SaO₂) of 88% or a resting PaO₂ between 55 and 60 mm Hg with evidence of pulmonary hypertension, cor pulmonale, or polycythemia with a hematocrit value more than 55%. Patients with a peripheral oxygen saturation (SpO₂) below 88% at rest also qualify [3,8].

Patients with good compliance with LTOT tend to have good clinical outcomes, such as requiring fewer hospitalizations [9]. However, a significant number of patients discontinue treatment without reevaluation [10-12]. Factors contributing to persistently poor compliance remain unclear. Despite several reports on the efficacy and compliance to LTOT in patients, most studies have focused on physicians’ views of prescription patterns or medical efficacy [8,9]. Only a few studies have considered the patients’ perspectives, usually using text analysis of structured interviews [13,14]. These studies showed that patients use oxygen as a tool for symptom management; however, the improvement in breathlessness by oxygen does not always meet expectations as perceived by patients. Factors affecting adherence may stem from patients’ perceptions of OT. In this study, we investigated patients’ perceptions of LTOT in a real-world clinical setting in Korea.

This cross-sectional survey study used descriptive open and closed-ended questionnaires. The survey was conducted at three university hospitals between December 1, 2017, and April 30, 2018. Patients older than 16 years with chronic hypoxemia due to chronic lung diseases who were currently using OT according to the LTOT criteria or who were required to use oxygen according to the LTOT criteria but avoided it, were included. Patients who did not meet the LTOT criteria and those who received OT after treatment for acute respiratory distress were excluded. The questionnaire was developed by five pulmonary specialists. The questionnaire consisted of 16 items, including five items on the timeframe of oxygen use and prescriptions of oxygen. The questionnaire included a benefit and adverse effects that patients experienced. There were also questions about patients’ perception of avoidance of home oxygen and portable oxygen use. The Korean and English versions of the questionnaire are provided in the Appendices 1, 2.

As insurance covers LTOT, its use continues to increase [15]. There is an increasing demand for the evaluation of LTOT with respect to intended medical effects as well as medical factors associated with compliance from the physicians’ perspective. To our knowledge, this is the first study to provide patients’ perspectives on LTOT in Korea. This study explored how patients feel and experience the LTOT in their lives.

LTOT improves survival in patients with severe hypoxemia who receive supplemental OT for more than 15 hr/day [4,5]. Ringbaek et al. [9] reported that home OT reduced the hospitalization rate from 92.7% to 63.8%. This benefit was particularly notable in the good compliant group. Previous domestic studies have exhibited good compliance more than 50% of patients who used OT for >15 hr/day and 15.4% who used OT for <8 hr/day [10,15,16]. Our study revealed poor adherence: only 30.1% of patients used OT for >15 hours, and 40.8% used OT for <8 hours. Since the study that reported 52% compliance was conducted before insurance coverage, these patients were considered to need OT because of physicians’ decisions or their own complaints of dyspnea, even though they did not meet the current insurance criteria [10]. Another study that reported improvement compared with those reported by the former study included patients with diseases that did not meet the insurance criteria for OT [16]. Their underlying disease included advanced lung cancer. As a result, 72% of the patients died within 1 year and 92% died within 2 years. All these studies were conducted single-center setting. However, our multicenter study includes patients with chronic lung diseases who used oxygen according to the LTOT criteria. This suggests that compliance with OT may vary depending on the underlying disease and the region. In a recent study, oxygen prescriptions for patients with neuromuscular diseases were more common than oxygen prescriptions for patients with chronic respiratory disease according to National Health Insurance Service data in Korea [17]. The characteristics of OT were considered not only for patients with hypoxemia, but also for those with underlying diseases and their severity.

In previous domestic studies, none or 38% of patients used portable oxygen [15,16]. Conversely, 46.4% of the respondents who used home oxygen also used portable oxygen. This finding may be attributed to the increased insurance coverage. In Korea, the National Health Insurance System extended insurance coverage to portable OT on January 1, 2017. As the economic burden decreased, the use of portable OT increased.

In our study, most patients felt that their symptoms had improved. More than 80% of the patients responded that their shortness of breath improved in both the good and poor adherence groups. The patients in both groups experienced local adverse effects related mouth and nose symptoms. However, no significant differences were observed between the good and poor adherence groups. In a recent domestic study, 36% patients voluntarily discontinued OT [15]. The cause of discontinuation was discomfort with OT, such as a dry mouth or nose. The number and types of local adverse effects were similar to those reported in previous studies, despite large differences in populations concerning underlying respiratory diseases, medical insurance coverage, and equipment types [18-20]. These adverse effects are often neglected or left untreated by physicians [8]. The reason for persistent local adverse effects could be that the majority had not been treated or discussed with healthcare professional [20]. Many commonly reported adverse effects can be treated, which could lead to a potentially positive effect on LTOT.

The most uncomfortable aspects of using portable oxygen were device-related complaints such as battery, noise, weight, and tube length. The longer patient used a portable oxygen device, the more uncomfortable they experienced that the short battery life. The battery was operated for approximately 3 hours depending on the flow at the pulse dose setting, and the recharge time was approximately 3 to 4 hours. The average noise was approximately 25 to 48 dB for home oxygen devices and about 42 to 48 dB for portable oxygen devices. Their average weight was approximately 3 kg, as measured using a portable oxygen device. The oxygen flow rate was approximately 1 to 3 L/min in a portable OT pulse dose setting. The tube lengths were 2.1 and 1.2 m for the home oxygen device and the portable device, respectively. Technical improvements were made to the oxygen devices, but the patients still experienced discomfort. While further development is necessary, inadequate guidance regarding the device may persist discomfort to use LTOT. Tubing length is a predictor of severe physical inactivity and time spent sitting [21]. Aguiar et al. [18] reported that a tubing length of 30 m did not lower the fraction of inspired oxygen supplied and may provide greater freedom for patients to move around at home. Further studies on the appropriate standards for oxygen devices are needed.

In our study, 90% of the patients with good adherence responded that they used oxygen according to the physicians’ prescription. However, among patients with poor compliance, only 36.7% conformed to physicians’ prescriptions. Patients with poor adherence reported that they used oxygen only when they experienced dyspnea (34.7%) or when they slept or engaged in activities of daily living (18.4% and 10.2%, respectively). This finding emphasized that patients with poor adherence misunderstood the medical role of OT. As a medical treatment LTOT improves the survival of patients with severe hypoxemia. Instead of considering OT as a medical treatment and following physicians’ prescriptions, patients with poor adherence used OT as a symptom reliever for complaints of dyspnea. A study on patients’ perceptions of OT conducted in the United Kingdom, reported a common misunderstanding that oxygen was commonly administered to relieve dyspnea [14]. In a previous domestic study, the reason for voluntary cessation of OT was the relief of subjective symptoms [15]. In the same study, the objective parameters of dyspnea did not differ significantly between the enrolled groups, such as the MRC scale and visual analogue scale. Physicians have focused on objective parameters related to compliance 8,9 . However, difference may not lay in objective medical effect but inpatients’ subjective perceptions. Patients’ perceptions of the purpose of OT could be the decisive factor in adherence.

In our study, the most common reason for avoiding home or portable oxygen was unwanted attention from onlookers. No significant differences were observed in terms of good or poor adherence. In one study, participants generally expressed that portable oxygen concentrators were helpful but received unwanted attention [22]. Williams et al. [23] noted that oxygen made their illness visible. Public use of OT seems to threaten the self-image of patients using both home and portable OTs [24,25]. The largest study on the adverse effects associated to LTOT, conducted in 1998, reported that patients using LTOT felt negative self-conscious [19]. Regardless of whether compliance is good or poor, the use of LTOT tends to be associated with a psychological barrier of significant self-consciousness and a sense of social stigma that makes patients feel weak and sick [26]. Consequently, negative self-image may be compromised, leading to embarrassment, worsening social isolation, and decreased patient adherence. Healthcare professionals provide sufficient support for the management of psychosocial barriers in patients using LTOT.

In our study, 50% of patients reported fear of dependency on OT as a reason for avoidance when requiring home OT, compared to 19.5% of patients with portable OT. Fear of dependency on OT was also related to reluctance among patients who had never used OT. One article reported that using oxygen was symbolic of a permanent decline in disease status or worsening of patients [27]. Patients with severe COPD recognize initiation of OT as a key milestone in the disease trajectory and in declining health [28,29]. LTOT is a marker of the terminal lung status and is often synonymous with disability and death. OT can demonstrate the recognition of disease severity, away from the unrealistic expectations about a better prognosis. The initial reaction to OT was fear of recognizing the severity of their disease and death. This psychosocial barrier may be the primary challenge in initiating LTOT in patients with advanced respiratory diseases.

Restriction of ambulation in daily living was another source of discomfort identified in our study. A previous study reported that the most prevalent adverse effects of LTOT are reduced mobility and physical activity [20]. Several studies have reported that OT may be associated with low physical activity in daily life [30,31]. Participants who used the LTOT show less independence in their activities of daily living [21,32]. The ambulation restriction did not appear to restrict the movements imposed by the stationary device. The patients identified their weaknesses and felt trapped in their lungs. Restricted activities of daily living are associated with depression and poor health status [24]. In some cases, depression gets intense and makes the individuals suicidal [33].

This study has several important implications. In clinical practice, to improve the adherence of patients, physicians have focused on objective factors or the medical efficacy of LTOT. However, most patients in both the good and poor adherence groups reported benefits and disadvantages associated OT. Both groups experienced improvement in their symptoms and revealed no evidence of deteriorating compliance with the use of oxygen due to adverse effect. We found that an important difference was patients’ misunderstanding of the effects of OT. However, in a previous study on physicians’ perspectives on home oxygen, physicians mainly emphasized the persistent use of home oxygen for >15 hours or not using too much oxygen [34]. The patients’ perceptions in our study highlight the need for health professionals to manage their perceptions of why they need oxygen. We found the psychosocial barriers that the patients in both good and poor adherence groups. Although it did not affect adherence, it may be a great obstacle to patient who are requiring oxygen or using it. Unwanted attention may interfere with initiation of portable OT, and fear of permanent use may make patients hesitate to initiate home OT. Restriction of daily activities will weigh on the patients with emotional burden. Identifying unrecognized perceptions and helping patients overcome negative perspectives could provide opportunities to improve initiation of OT and to explore what it is like living in a life-limiting condition. Sharing these experiences may help individuals make informed choices regarding advanced care plans for terminal chronic respiratory diseases.