Patients receiving mechanical ventilation in the intensive care unit (ICU) frequently develop ICU-acquired weakness - a condition marked by widespread muscle loss and weakness caused by prolonged bed rest, severe illness, and systemic inflammation. This complication can lengthen time on the ventilator, extend ICU stays, and lead to lasting physical disability. Standard rehabilitation therapies in the ICU have limited ability to slow muscle loss because critically ill patients cannot tolerate high levels of exercise.
Blood flow restriction training (BFRT) is a rehabilitation technique that uses an inflatable cuff on the upper leg to partially restrict blood flow during low-intensity exercise. This approach is known to stimulate muscle growth and preserve strength with much lower physical effort than traditional strength training, making it a promising option for vulnerable ICU patients.
This randomized controlled trial is designed to test the safety and effectiveness of BFRT in mechanically ventilated adults with ICU-acquired weakness. A total of 120 eligible patients will be randomly divided into three groups:
A control group receiving standard ICU medical care and routine rehabilitation A group receiving standard care plus BFRT at 40% of individual limb occlusion pressure A group receiving standard care plus BFRT at 60% of individual limb occlusion pressure All patients will receive 2 weeks of intervention. The research team will measure and compare muscle strength, lower limb muscle size (via ultrasound), blood inflammatory markers, duration of mechanical ventilation, length of ICU stay, and ventilator weaning success rates across the three groups.
This study aims to determine whether adding BFRT to standard rehabilitation can improve muscle function, reduce systemic inflammation, and shorten hospital recovery time for these patients, and which pressure level provides the optimal balance of benefits and safety.
Age ≥ 18 years;
Received invasive mechanical ventilation for ≥ 48 hours;
Meets the clinical diagnosis criteria for ICUAW: The patient has reached a level of consciousness that allows for reliable assessment of voluntary muscle strength, is able to execute standardized motor commands, has an MRC-SS < 48 points, and has no other clearly identifiable cause that explains the muscle weakness;
RASS score of -1 to 0, and is able to cooperate with the prescribed muscle strength assessment and rehabilitation training;
The presence of pre-existing central or peripheral nervous system diseases, neuromuscular diseases, or severe motor function disorders that significantly affect limb strength or motor function prior to ICU admission;
The presence of active deep vein thrombosis, pulmonary embolism, significant peripheral arterial disease, limb ischemia, or other severe lower limb vascular diseases;
Severe coagulation function abnormalities, active bleeding, or a clinically judged unacceptable risk of thrombosis/hemorrhage;
The presence of fractures, open wounds, local infections, significant skin damage, or other conditions in the target lower limb that are unsuitable for cuff compression and exercise training;
Parallel
Blood flow restriction training
Other interventionBlood flow restriction training (BFRT) is administered using a wireless automated pneumatic cuff system (BFR Cuffs 2.0) placed on the proximal thigh. Training pressure is individually calibrated as a percentage of each patient's resting limb occlusion pressure (LOP), measured via the device's built-in pressure sensor and algorithm to accommodate differences in limb circumference and vascular tone. The intervention partially restricts venous return while preserving arterial inflow, combining low-intensity lower-extremity resistance movements with localized hypoxic and metabolic stress to stimulate muscle anabolic pathways. It is delivered at very low perceived exertion (Borg RPE 9-11) with continuous bedside vital sign monitoring, specifically adapted for hemodynamically stable critically ill patients with ICU-acquired weakness.
Standard ICU Care and Routine Rehabilitation
Other interventionThis arm serves as the control reference, delivering the standard-of-care clinical pathway for critically ill mechanically ventilated patients. It includes comprehensive ICU medical management (anti-infective treatment, ventilatory support, enteral nutrition, hemodynamic maintenance, electrolyte balance correction, and evidence-based nursing bundles) plus standardized early rehabilitation administered by certified therapists per institutional ICU rehabilitation protocols. No investigational blood flow restriction intervention is applied in this group; all care follows routine clinical practice without additional study-specific exercise modifications.
medical research council sum score
The Medical Research Council sum score (MRC-SS) is a validated clinical scale for evaluating global limb muscle strength in critically ill patients. It assesses 6 bilateral muscle actions: shoulder abduction, elbow flexion, wrist extension, hip flexion, knee extension, and ankle dorsiflexion. Each item is scored from 0 (no visible muscle contraction) to 5 (full strength against maximum resistance), yielding a total score ranging from 0 to 60. A lower score indicates more severe generalized muscle weakness. All assessments are performed by trained evaluators blinded to patient group assignment.
Lower Limb Muscle Morphology Assessed by Ultrasound
Standardized musculoskeletal ultrasound is used to quantitatively evaluate lower limb muscle morphology. Four parameters are measured at fixed anatomical landmarks: cross-sectional area (CSA) and muscle thickness (MT) of the rectus femoris (15 cm above the superior patellar border), and CSA and MT of the medial gastrocnemius (10 cm above the medial malleolus). All scans are performed by sonographers blinded to group allocation, with the mean value of three independent measurements used for statistical analysis. Changes in these parameters reflect the degree of muscle atrophy or preservation over the intervention period.
Serum Inflammatory Cytokine Levels
Fasting venous blood samples are collected in the early morning (6:00-8:00) at each time point. Serum concentrations of three pro-inflammatory cytokines - tumor necrosis factor-alpha (TNF-α), interleukin-6 (IL-6), and interleukin-8 (IL-8) - are measured using enzyme-linked immunosorbent assay (ELISA) kits following standardized laboratory protocols. All assays are performed by laboratory technicians blinded to group assignment. These biomarkers reflect the magnitude of systemic inflammatory response, a core pathophysiological driver of ICU-acquired weakness.
Duration of Invasive Mechanical Ventilation
Total duration of invasive mechanical ventilation is defined as the number of consecutive days from study enrollment to successful ventilator weaning. Successful weaning is confirmed as sustained liberation from invasive mechanical ventilation for at least 48 hours without requiring re-intubation. Data are extracted from standardized electronic medical records and adjudicated in accordance with institutional critical care ventilator weaning protocols.
ICU Length of Stay
ICU length of stay is defined as the total number of consecutive days from the date of study enrollment to the date of ICU discharge. Discharge endpoints include transfer to a general medical ward, step-down care unit, or direct hospital discharge. All data are extracted from standardized electronic medical records and verified by study coordinators in accordance with institutional admission and discharge protocols.
Ventilator Weaning Success Rate
Ventilator weaning success rate is defined as the proportion of patients who achieve successful liberation from invasive mechanical ventilation without re-intubation within 48 hours, relative to the total number of enrolled patients in each study group. Successful weaning is confirmed as sustained spontaneous breathing without invasive ventilatory support for at least 48 consecutive hours. All outcomes are adjudicated in accordance with institutional standardized critical care weaning protocols, with data extracted from verified electronic medical records.
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