ICU Associated Weakness and Bedside Ultrasound Assessment

BACKGROUND

Physical weakness is a common during and after critical illness. Weakness can develop for multiple reasons, but it can be generally be grouped into three overlapping categories:

1. Nervous system dysfunction - weakness can result from impairments in the nervous system control of muscles;
2. Muscle size reductions (i.e. sarcopenia) - muscles become smaller with disuse, and;
3. Muscle force reductions (i.e. dynapenia) - muscles develop contractile impairments.

In critical care, diagnostic criteria have been developed for a syndrome of weakness called intensive care unit-acquired weakness (ICU-AW). ICU-AW has important clinical implications. It is associated with delayed ventilator weaning, increased mortality, and longer lengths of stay in the hospital. ICU-AW can also have consequences for patients after they leave the hospital. ICU-AW can be implicated in impairments in quality of life and physical function such as difficulty climbing stairs, and delays in returning to work.

Diagnosing ICU-AW is not trivial and it is centered on assessments targeted primarily to assessing dynapenia. The diagnostic criteria are clear but making the diagnosis relies on the active participation of patients, and the reliable subjective assessment by clinicians at the bedside. Factors such as sedation, restraint use, paralytic medications, pain, and dressings can all confound the assessment of a patient's strength.

To augment patient assessments, it is possible that assessments of sarcopenia might be helpful in highlighting who might be at risk for muscle dysfunction in the ICU.

RESEARCH QUESTION AND OBJECTIVES Do serial measurements of tibialis anterior muscle cross-sectional area (a muscle in the leg) using bedside ultrasound correlate with clinical weakness in people admitted to the ICU for sepsis?

Primary Outcome:

Determine if the rates of decline of tibialis anterior muscle cross-sectional areas (%/day) measured by bedside ultrasound on participants admitted to an ICU for sepsis correlate with bedside clinical measures of strength using the medical research council (MRC) sum score (a score between 0 and 60).

Secondary Outcomes:

Determine if rates of decline of tibialis anterior muscle cross-sectional areas correlate with:

1. Ankle dorsiflexion strength, measured using the Medical Research Council (MRC) Scale for muscle strength (a score between 0 and 5);
2. Illness severity at admission to the ICU, measured by the Sequential Organ Failure Assessment (SOFA) score (a score between 0 and 24);
3. Duration of mechanical ventilation (days),
4. Duration of ICU length of stay (days), and;
5. Duration of hospital length of stay (days).

METHOD Each day, new admissions to a mixed medical-surgical ICU will be screened. Any person admitted with a diagnosis of sepsis will be considered for invitation to the study. Potential participants will be excluded if they are children (age < 18 years), if they have preexisting diagnoses that would plausibly affect the size of the muscles in their leg, or if they have medical conditions that would preclude an assessment of their strength. Participants who are appropriate for inclusion in the study will be approached for informed consent.

For participants who consent, every second day the cross-sectional area of the tibialis anterior muscle bulk on each leg will be measured (cm^2) using bedside ultrasound. These measurements will be accompanied by a clinical assessment of strength using the Medical Research Council (MRC) strength scale on six muscle groups bilaterally (shoulder abduction, elbow flexion, wrist extension, hip flexion, knee extension, and ankle dorsiflexion). Participants will continue to be evaluated every other day until they leave the ICU, or until their 14th day of admission to the ICU. Chart reviews will supplement these data to allow for the determination of the secondary objectives (e.g. SOFA scores, hospital lengths of stay).