This mixed-methods study comprising a 3-arm pilot RCT and a qualitative study aims to investigate the preliminary effects and feasibility of a home-based combined activity and cognitive intervention for ICU survivors (COMBAT-ICU). Adopting a 3-arm design with COMBAT-ICU, exercise and attention placebo study arms will enable us to evaluate the added effects, if any, of the novel combined intervention compared with the standard exercise-only rehabilitation strategy and attention placebo. Data triangulation from quantitative and qualitative aspects can facilitate result interpretation. The study's objectives are:

1. To evaluate the preliminary effects of the COMBAT-ICU intervention for ICU survivors on PICS, physical, mental and cognitive outcomes, HRQoL, unplanned re-hospitalisation rate, and mortality.
2. To explore the feasibility and acceptability of the COMBAT-ICU intervention and ICU survivors' intervention engagement experience.

The hypothesis of the first objective is that upon completion of the COMBAT-ICU intervention, ICU survivors will have reduced PICS, improved physical function, mental health, cognition and HRQoL, and reduced unplanned readmissions and mortality compared with the exercise and attention placebo groups at post-intervention and 3 months thereafter. While the hypothesis of the second objective is that the COMBAT-ICU intervention is feasible and acceptable for ICU survivors.

With the growing cohort of patients surviving after ICU treatment, the long-term consequences of critical illness have gained increased attention in the past decade. It is common for ICU survivors to experience long-term impairments in one or more domains of physical, cognitive or psychological functioning that persist beyond acute care hospitalization for a critical illness, impairments that are collectively known as post-intensive care syndrome (PICS).

As PICS is a relatively new syndrome, research is accumulating on different approaches to tackling it. There are several limitations on previous studies, such as only a single strategy, an exercise intervention, was tested to manage physical impairment or PICS as a whole, or no beneficial effect was documented on health-related QoL, leaving a significant gap in the literature. Hence, a multimodal rehabilitative approach is needed for this vulnerable cohort in promoting physical, functional and cognitive performance so as to develop effective strategies to prevent and manage PICS among ICU survivors, particularly during the early post-discharge period.

This study is mixed-methods comprising a 3-arm pilot RCT and a qualitative study aims to investigate the preliminary effects and feasibility of a home-based combined activity and cognitive intervention for ICU survivors (COMBAT-ICU), with assessments measured at baseline, immediate post-intervention and 3 months post-intervention. It will be conducted in three public hospitals in Hong Kong. Patients fulfilling the following eligibility criteria will be recruited: 1) Chinese adults aged ≥18; 2) has been admitted to ICU for at least 4 days; 3) has been discharged home; 4) was able to perform basic activities of daily living before ICU admission; 5) is living with family; 6) has an electronic device that can access the internet (patient/family); 7) is able to walk for at least 10 metres (assisted or unassisted).

Participants will be randomly allocated in a 1:1:1 ratio to the COMBAT-ICU, exercise or attention placebo groups.

For the COMBAT-ICU group, they will receive an intervention which will last for 8 weeks, with 3 sessions per week. A blended training platform with supervised in-person home visits and a real-time supervised online and unsupervised self practice approach will be used to deliver the intervention, with the platform gradually shifted from home visits to unsupervised self-practice according to participants' physical functioning level. Family caregivers will be involved in the intervention, so that they can facilitate home-based training. Each intervention session will last for 80 minutes and comprise 45 minutes of exercise training, a 5-minute break and 30 minutes of cognitive training. Moreover, all participants in the COMBAT-ICU group will be invited to complete a satisfaction survey and semi-structured qualitative interview, which will focus on exploring the acceptability and perceived effects from participants' perspective.

For the exercise group, they will receive an 8-week, home-based, exercise intervention which is the same as that of the exercise component of the COMBAT-ICU intervention, 3 sessions per week, and 45 minutes per session, but will not receive any structured cognitive training.

For the attention placebo group, they will receive a telephone call every 2 weeks, with the conversation focused on information provision and brief counselling relating to their health conditions, in order to reduce the potential bias from greater attention for the COMBAT-ICU and exercise groups. They will also receive the routine care provided by the healthcare system, including medical follow-ups with the clinical team, without structured out-patient rehabilitation services.

Evaluative outcomes will be measured at baseline (T0), immediate post-intervention (T1) and 3 months post-intervention (T2), and include Post-Intensive Care Syndrome Questionnaire (PICSQ), muscle mass and strength, physical performance, cognition function, psychological distress, Health-related quality of life (HRQoL), hospital readmission and mortality.

Inclusion Criteria:

1. Chinese adults aged ≥18
2. has been admitted to ICU for at least 4 days
3. discharged home
4. able to perform basic activities of daily living before ICU admission
5. living with family
6. has an electronic device that can access the internet (patient/family)
7. able to walk for at least 10 metres (assisted or unassisted)

Exclusion Criteria:

1. cannot read Chinese
2. has musculoskeletal injury precluding exercise training
3. is receiving structured out-patient pulmonary or cardiac rehabilitation after discharge
4. has clinically evident dementia or significant impairment from an acute brain problem (e.g. traumatic brain injury, stroke, subarachnoid haemorrhage or hypoxic brain injury) that precludes following the study protocol
5. has prolonged length of stay (≥28 days) in the step-down wards