1. Introduction

The subacute consequences of COVID-19, collectively referred to as PASC or long COVID, include a wide range of symptoms that persist for 4-12 weeks after an acute infection. These include chronic fatigue, shortness of breath, decreased tolerance to physical exertion, cognitive impairments, depression, anxiety disorders, visual and auditory impairments [3-5]. These conditions are detected not only in patients with a severe course of the disease, but also in individuals who have had mild forms of the infection and have undergone outpatient treatment [6].

Unlike inpatient care, outpatient rehabilitation should be accessible, cost-effective, and scalable, which is especially relevant for low- and middle-income countries, including CIS countries. Rehabilitation measures should begin in intensive care units when the patient's condition stabilizes and continue after completing treatment in the hospital or day hospital, then in outpatient and home conditions or sanatorium conditions [4]. The tasks of medical rehabilitation are restoring the functions of external respiration, transport, and utilization of oxygen by tissues, organs, and systems, restoring tolerance to stress, psycho-emotional stability, daily activity, and work capacity [3,4]. At all stages of medical rehabilitation, it is recommended to observe anti-epidemic measures and utilize telemedicine and information technology capabilities in distance learning [5,6].

Depending on the predominant damage to a particular system, rehabilitation programs are carried out using an individual approach. Neurological and sensory complications after COVID-19 are of particular importance. Cognitive deficit, described by patients as "brain fog," memory and attention impairments, visual impairments, and hearing loss significantly limit social activity and work capacity, forming long-term economic losses [7-9].

2. Purpose of the Research

The aim of this systematic review is to summarize current data on the rehabilitation of patients after COVID-19 in outpatient settings, focusing on epidemiology, clinical aspects, diagnostics, complications, and optimization of rehabilitation strategies.

3. Materials and Methods

Scientific literature presented in the Scopus, Web of Science, PubMed, CyberLeninka, and eLIBRARY Scientific Electronic Library databases was analyzed, including original research, clinical cases, and literature reviews for the period 2019-2022. The search was conducted using the following keywords: "rehabilitation," "COVID-19," "post-covid syndrome," "physiotherapy," "breathing exercises," and "therapeutic exercises." The focus was on studying the methods of restorative therapy used at different stages of patient rehabilitation following COVID-19.

4. Results

According to meta-analyses, post-COVID symptoms are detected in 10-30% of patients who had the infection without hospitalization and in more than 50% of individuals after inpatient treatment [4,6]. The most common complaints in the early period are fatigue, shortness of breath, and decreased physical performance, while cognitive and sensory impairments tend to dominate in the long term [7].

Medical rehabilitation is carried out in three stages. The first stage is conducted in inpatient settings in early medical rehabilitation departments. The second stage is also carried out in inpatient settings in specialized medical rehabilitation departments for patients with disorders of the peripheral nervous, musculoskeletal, and central nervous systems, as well as for somatic diseases. The third stage is conducted in outpatient settings and day hospitals - in the outpatient departments of polyclinics or in the medical rehabilitation departments of day hospitals.

Early rehabilitation (first stage) aims to restore basic physiological functions and includes:

• breathing exercises and elements of pulmonary rehabilitation;

• gradual aerobic training;

• teaching patients methods of self-monitoring and energy conservation.

Beginning rehabilitation in the first 4-6 weeks is associated with faster functional recovery and a decrease in the severity of symptoms [13-15].

The program of the first stage includes physiotherapeutic methods: high-flow oxygen therapy, low-frequency laser therapy, infrared laser blood irradiation, drug electrophoresis of bronchodilators, diaphragmatic breathing, pursed-lip breathing, respiratory and therapeutic exercises [11,12]. If necessary, positioning, active cycle of breathing technique, percussion, and vibration are used to clear the airways [11]. Prone positioning, early mobilization, and therapeutic exercise under heart rate, blood pressure, and oxygen saturation monitoring are also effective [13,14]. Moderate physical activity has antioxidant and anti-inflammatory effects, reduces endothelial dysfunction and the risk of thromboembolic complications [15].

In the second stage, rehabilitation measures are continued in a specialized hospital setting, taking into account the patient's condition. In severe cases without progressive respiratory failure, oxygen therapy and laboratory monitoring (coagulation tests, electrolytes, etc.) may be required [1,4]. The effectiveness of telerehabilitation has been confirmed by studies demonstrating its comparability with inpatient pulmonary rehabilitation.

Late rehabilitation (third stage) requires a multidisciplinary approach and includes:

• cognitive rehabilitation and neuropsychological support;

• audiological and ophthalmological rehabilitation;

• psychosocial interventions;

• telerehabilitation and digital long-term monitoring programs [16-18].

In outpatient practice, post-COVID-19 diagnosis is based on clinical assessment, a 6-minute walk test, neurocognitive screening (MoCA, MMSE), audiometry, and ophthalmological examination. Breathing exercises, strength and interval training, swimming, and walking with gradual expansion of physical activity are used. Physiotherapy includes neuromuscular stimulation, magnetotherapy, electrosleep therapy, massage, acupuncture, and other methods.

5. Discussion

The economic consequences of post-COVID-19 are significant. The increase in the number of outpatient visits, prolonged temporary disability, and decreased participation in work activities result in multibillion-dollar indirect losses exceeding the costs of treating the acute phase of the disease [10].

Early rehabilitation primarily focuses on restoring somatic functions, while later stages aim to correct cognitive and sensory impairments. The outpatient format allows for coverage of wide patient groups; however, it requires standardization and integration with primary healthcare [19-24].

Risk stratification, which allows for optimal resource allocation and directing intensive rehabilitation programs to patients with a high risk of long-term disability, is of particular importance [25-27].

This review confirms that outpatient rehabilitation is a central element of post-COVID care and requires a systemic, phased, and multidisciplinary approach.

6. Conclusions

Rehabilitation of patients after COVID-19 in outpatient settings is an essential component of the modern healthcare system. Early and late rehabilitation address different, yet interrelated clinical challenges. The implementation of phased, evidence-based outpatient rehabilitation programs has the potential to significantly reduce long-term morbidity, disability, and the economic burden of the pandemic.