Neuromuscular Electrical Stimulation in Critically Ill Patients Aged 80 and Over

Change in Skeletal Muscle Mass

For the assessment of muscle mass, the thickness of the quadriceps muscle-composed of the vastus intermedius and rectus femoris-and the anterior tibialis muscle will be measured using ultrasonography. For quadriceps thickness, the reference point will be the midpoint between the anterior superior iliac spine and the superior pole of the patella. At this point, the following measurements will be taken: vastus intermedius (VI), rectus femoris (RF), and total quadriceps thickness (TQ). For the anterior tibialis muscle, the reference point will be the first third of the distance between the lateral condyle of the tibia and the upper edge of the lateral malleolus. At this reference point, the image will be frozen and the thickness of the anterior tibialis muscle will be measured. For each muscle, three consecutive measurements will be taken, and the average value will be recorded in centimeters.

Change in Handgrip Strength

Handgrip strength (HS) will be assessed using a JAMAR® digital dynamometer. Grip strength will be measured in both the dominant and non-dominant hands. During the assessment, the participant will be in a long sitting position (sitting upright in bed), with shoulders adducted and without rotation, the elbow flexed at 90° close to the body, and the forearm and wrist in a neutral position. The assessed arm will be supported on a pillow. The examiner will hold the dynamometer in a vertical position, and the participant will exert their maximum grip strength for 3 seconds. Grip strength will be measured three times on each hand alternately, and the highest recorded value will be used for analysis.

Change in Peripheral Muscle Strength

Peripheral muscle strength will be assessed using the Medical Research Council Sum Score (MRC-SS), which evaluates the global peripheral muscle strength of six major muscle groups during functional movements (shoulder abduction, elbow flexion, wrist extension, hip flexion, knee extension, and ankle dorsiflexion) on each side of the body. Each group is rated from 0 (no visible contraction) to 5 (normal strength throughout the full range of motion). Each participant will be assigned a total score ranging from 0 (total paralysis) to 60 (normal strength). Assessments will be performed from right to left and from proximal to distal, following that same sequence. Up to three optimal attempts will be allowed per muscle group, with a rest period of at least 30 seconds between attempts.

Change in Inspiratory Muscle Strength

Inspiratory muscle strength will be assessed using a digital manometer (MicroRPM®, Vyaire Medical, Hoechberg, Germany). The evaluations will follow the American Thoracic Society (ATS) recommendations for respiratory muscle strength testing. Participants will be instructed to: i) perform a rapid exhalation down to residual volume, and ii) execute a maximal inhalation "with as much force as possible." The result from this measurement will be compared against predictive equations for maximal respiratory pressures, which vary based on sex and age. The highest value from three maneuvers with less than 10% variation will be recorded, with a 1-minute rest between each attempt.

Change in ICU Functionality

Functionality in the ICU will be assessed using the Chilean version of the Functional Status Score for the Intensive Care Unit (FSS-ICU). The FSS-ICU measures the level of physical assistance required for five functional activities in the intensive care setting: rolling in bed, transitioning from supine to sitting, sitting at the edge of the bed, transferring from the bed to standing, and walking. Walking will only be assessed if the participant is able to complete a 30-meter walk. Each activity is scored from 0 points (unable to perform) to 7 points (complete independence). The total score is the sum of the scores for each completed activity, with a higher score indicating greater functional mobility.