Design

This research is a consecutive, non-randomized, pre-post-intervention proof-of-concept study designed to evaluate the efficacy and safety of the FlexO2 device in patients receiving long-term oxygen therapy (LTOT). The trial was conducted at the Karolinska University Hospital, Faculty of Medicine, Department of Respiratory Medicine and Allergology, Solna, Stockholm.

Participants

Thirty patients were recruited from the regular flow of patients at the Department of Respiratory Medicine, of whom twenty-six met the inclusion criteria.

The inclusion criteria were patients with chronic respiratory insufficiency receiving long-term oxygen therapy (LTOT) for at least six months at two different flow settings (at rest and during activity) and the ability to understand the study procedures and provide informed consent.

Exclusion criteria included patients with increased PCO2 above 6 kPa or 45 mmHg, language difficulties or reduced cognitive ability and those who had recently initiated oxygen therapy.

Intervention and control

FlexO2 is a patient-controlled oxygen flow selector that allows the user to quickly switch between two preset oxygen doses for activity and rest. The device was connected to the patient’s nasal cannula, allowing them to modify their oxygen dose without needing to access the oxygen concentrator. The two doses are preset by healthcare professionals based on prescribed oxygen flow. FlexO2 is worn around the neck (Fig. 1), relieving the patient’s ears from strain. It is connected at the bottom of the valve to the tube from the oxygen concentrator and on top of the nasal cannula [15]. The device is currently CE marked as a Class IIa medical device. Is is approved under the Medical Devices Directive (MDD 93/42/EEC), and has a valid exemption while the MDR certification process is ongoing.

Fig. 1

Illustration showing the FlexO2 oxygen flow control device worn around the neck, with nasal cannula in place

All participants received the FlexO2 device. The patient’s oxygen dose at rest was determined based on an arterial blood gas analysis, while the dose during activity was established using the six-minute walk test (6MWT). The oxygen dose for each setting was initially determined and prescribed by a physician and then calibrated by an oxygen nurse according to the patient’s needs as part of their usual care. Each month, the device was replaced with a new one.

A within-subject design was implemented, where each participant served as their control. Outcomes were compared at enrollment and after three months of FlexO2 usage to gauge the intervention’s impact. This approach allowed for direct assessment of the device’s effect on each patient. Patients were instructed to return to traditional oxygen flow adjustment as a contingency measure in case of problems or device malfunction. An oxygen therapy nurse conducted telephone follow-ups to check on the device’s function.

Data collection and instruments

Interviews and structured questionnaire forms were used to assess the function of the oxygen regulator and related questions. Data was collected from participants at baseline and after three months, including (1) demographic data, (2) clinical data related to the use and handling of the FlexO2 device, and (3) quality of life and health assessments using the EQ-5D questionnaire and the COPD Assessment Test (CAT) [17, 18].

Participants were scheduled for nurse visits during which practical handling tests were conducted. During these visits, an oxygen therapy nurse observed each participant’s ability to adjust the oxygen dose directly on the concentrator and remotely using the FlexO2 device. The nurse noted any difficulties or errors (e.g., challenges in adjusting the dose, tubing tangling, or airflow issues), and provided on-site guidance when necessary.

To complement the in-person assessments, telephone follow-ups were conducted periodically by the oxygen therapy nurse. These calls served to ensure the device was functioning correctly, to answer participant queries, and to record any issues or adverse events reported between the scheduled visits.

Outcomes

The primary outcomes were:

(A)

Overall quality of life - assessed using Visual Analogue Scale (VAS, 0-100).

(B)

Ability to be active at home - assessed using Visual Analogue Scale (VAS, 0-100).

(C)

Ease of adjusting oxygen dose - assessed using Visual Analogue Scale (VAS, 0-100).

(D)

Daily frequency of oxygen dose adjustments - assessed by patient-reported counts.

The secondary outcomes focused on oxygen dose adjustments, specifically the frequency and ease of adjustments in several different situations, along with overall patient satisfaction and the user-friendliness of the FlexO2 device. Secondary outcomes also include EQ-5D and the COPD Assessment Test (CAT).

Patients were asked about their overall satisfaction with FlexO2 and to report any problems or device-related safety issues experienced during the three-month study period.

All outcomes were measured at baseline and at the 3-month follow-up to evaluate changes associated with FlexO2 use.

Statistical analyses

Descriptive statistics were used to summarize baseline characteristics. Continuous variables were expressed as medians with interquartile ranges (IQRs) due to the non-parametric nature of the data.

A minimum important difference of 2 points was used to assess changes in the CAT score [19].

To convert the EQ-5D-5 L to an index, the guidelines established in the relevant literature were followed, utilizing country-specific value sets. For this purpose, the most recent study conducted in Sweden by Sun et al. (2022) was referenced [20].

The minimally important difference (MID) was applied to evaluate whether changes in scores were clinically significant. In the context of chronic obstructive pulmonary disease (COPD) and other respiratory diseases, a MID of 0.051 for utility indices and 6.9 points for Visual Analogue Scale (VAS) scores are considered clinically important differences, as suggested by Nolan et al. [21].

The Wilcoxon signed-rank test was used to compare paired continuous variables, and McNemar’s test was used for paired categorical data. A p-value of less than 0.05 was considered statistically significant. Data was visualized using dot plots, with the median as the center dot and Q1 and Q3 as the lower and upper whiskers. All statistical analyses were done using R (version 4.4.0) [22].

Data availability declaration

The data supporting the findings of this study will be made available upon request.

Clinical trial number

Clinical trial number is not applicable. The study was registered locally in Stockholm. As it was not initially listed on clinicaltrials.gov, retrospective registration was not possible.

Ethics, consent to participate, and consent to publish

Ethical approvalwas obtained from the Regional Ethical Review Board in Stockholm (EPN 2017/673 − 31/1). The trial was conducted during the period of September 2017 to November 2022.

Written informed consent was obtained from all participants before their inclusion in the study, covering their participation and the use of their data for publication. All procedures were performed in accordance with the ethical standards of the institutional and national committees and with the Helsinki Declaration [16].

Funding declaration

This study was supported by the Swedish Heart-Lung Foundation (Hjärt-Lungfonden). FlexO2 devices were provided by Lungflex AB, Ljungby, Sweden at no cost. Neither the funding body nor the device manufacturer participated in the study design, data collection, analysis, interpretation, or manuscript preparation.