Post-Covid syndrome, also known as long Covid, is a clinical condition in which patients experience long term symptoms after Covid-19 infection. Treatment options for post-Covid are not effective. Therefore, there is an urgent need for a novel therapy. The first study results of HBOT in post-Covid patients are promising. Previous research from Israel has shown improvements in quality of life after HBOT. However, long term results are unknown. Therefore, this study aims to evaluate quality of life at one year after hyperbaric oxygen therapy in post-Covid patients with cognitive symptoms. It is hypothesized that quality of life at one year after HBOT is improved. Furthermore, this study aims to evaluate return to work after HBOT. To our knowledge this was not done before. An observational prospective cohort study will be conducted to answer the research questions. All post-Covid patients who are treated with hyperbaric oxygen therapy in participating centers, will be eligible for inclusion. Questionnaires and medical doctor consultations will be used in order to collect all data.

There are no risks for participants, since only 7 questionnaires are not part of standard clinical care. The burden is approximately 40 minutes extra in total for participants, compared to standard clinical care.

The study design is a prospective observational cohort study. Questionnaires and medical doctor consultations will be used in order to collect all data. All patients treated with HBOT have medical doctor consultations at baseline and every 10th session of HBOT (standard clinical care).

At baseline, the following characteristics will be collected: gender, age, BMI, medical history, Covid infection information, vaccination status, work status before Covid infection, previous Covid treatments, hospital and/or intensive care unit admission during Covid infection and smoking status. Furthermore, all patients treated are asked to fill out the SF-36 and EQ-5D questionnaires, a proprietary post-Covid symptoms questionnaire, and a questionnaire regaring work status. These questionnaires are repeated after 20, 40 (50) sessions of HBOT and after 3 and 12 months after the last treatment session.

During the following medical doctor consultations, side effects, changes in medication and interruptions of HBOT will be recorded as well to monitor compliance.

An interim analysis will be performed after 6 months to continue or stop treatments, based on the clinical results (as measured with the Physical Component Score of the SF-36 questionnaire). The minimal clinically important difference (MCID) to warrant early termination of therapy is if <5% of patients improves 3 points. The upper limit (and reason to continue) is if >50% achieve an MCID of 7 points.

Inclusion Criteria:

• Long COVID patients who are reffered for treatment with hyperbaric oxygen therapy
• Patients are suffering from cognitive symptoms for &gt;3 months after Covid infection

Exclusion Criteria:

• Patients who are not able to fill in questionnaires and informed consent.
• Patients who can't read or do not understand the Dutch language

The population will consist of post-Covid patients from the Netherlands, who are treated with hyperbaric oxygen therapy at several different treatment centers. All patients are adults and will receive standard clinical hyperbaric oxygen therapy at these clinics.

The data is retrieved from patient files (after informed consent). Even though the data is pseudonymised, there is too much risk of confidentialty breach.