This study aims to determine whether shear wave elastography (SWE), a non-invasive ultrasound technique that measures nerve stiffness, can help detect ICU-acquired weakness (ICU-AW) early in critically ill patients. Adults receiving mechanical ventilation in the ICU will undergo ultrasound examinations of the median and tibial nerves on Days 1, 4, and 7. The study will evaluate whether early changes in nerve elasticity can predict ICU-AW, which is usually diagnosed later using a muscle strength score that requires patient cooperation.
Age ≥ 18 years;
Newly admitted to ICU with an expected ICU stay > 7 days;
Initiated on mechanical ventilation within 24 hours of admission, with an expected ventilation duration > 48 hours;
Patient or legally authorized representative provides written informed consent.
Known pre-existing neuromuscular diseases (e.g., myasthenia gravis, Guillain-Barré syndrome, amyotrophic lateral sclerosis);
Pre-existing limb dysfunction that would interfere with muscle strength assessment (e.g., hemiplegia, paraplegia, severe arthritis);
Presence of acute trauma, surgery, skin breakdown, infection, or severe edema at the measurement sites (wrist, elbow, ankle) that would interfere with ultrasound probe placement;
Pregnant or lactating women;
Critically ill adults on mechanical ventilation with an anticipated ICU stay greater than 7 days.
Cohort
Prospective
Nerve Ultrasound with Shear Wave Elastography
Diagnostic testPatients will undergo non-invasive ultrasound examinations of the median nerve and tibial nerve at the bedside on days 1, 4, and 7. The examination includes Shear Wave Elastography (SWE) to quantify nerve stiffness (elasticity) and B-mode imaging to measure nerve cross-sectional area (CSA). This is a purely observational procedure and does not alter patient management.
Diagnostic Accuracy of Nerve SWE on Day 1 for Predicting ICU-AW on Day 7
Area Under the Receiver Operating Characteristic Curve (AUC) for the mean elasticity value (measured in kilopascals, kPa) of the median and tibial nerves, assessed separately at three time points after ICU admission: Day 1 - to predict ICU-AW diagnosed on Day 7 Day 7 - for concurrent diagnosis of ICU-AW (elastography and MRC assessed independently, blinded to each other) ICU-Acquired Weakness (ICU-AW) is defined as a Medical Research Council (MRC) sum score of less than 48 points.
Diagnostic Accuracy of Nerve SWE on Day 4 for Predicting ICU-AW on Day 7
Area Under the Receiver Operating Characteristic Curve (AUC) for the mean elasticity value (measured in kilopascals, kPa) of the median and tibial nerves, assessed separately at three time points after ICU admission: Day 4 - to predict ICU-AW diagnosed on Day 7 Day 7 - for concurrent diagnosis of ICU-AW (elastography and MRC assessed independently, blinded to each other) ICU-Acquired Weakness (ICU-AW) is defined as a Medical Research Council (MRC) sum score of less than 48 points.
Diagnostic Accuracy of Nerve SWE on Day 7 for Diagnosing ICU-AW on Day 7
Area Under the Receiver Operating Characteristic Curve (AUC) for the mean elasticity value (measured in kilopascals, kPa) of the median and tibial nerves, assessed separately at three time points after ICU admission: Day 7 - for concurrent diagnosis of ICU-AW (elastography and MRC assessed independently, blinded to each other) ICU-Acquired Weakness (ICU-AW) is defined as a Medical Research Council (MRC) sum score of less than 48 points.
Change in Nerve Elasticity
Absolute and relative change in the shear wave elastography (SWE) value (in kPa) of the median and tibial nerves from baseline (Day 1) to Day 7.
Correlation between Nerve Elasticity and Disease Severity
Spearman's correlation coefficient will be calculated to assess the relationship between the baseline (Day 7) nerve SWE values and the baseline Sequential Organ Failure Assessment (SOFA) score.
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