ICU Associated Weakness and Bedside Ultrasound Assessment

ICU-associated weakness is a common experience for people following a critical illness. It is associated with important patient and system-relevant outcomes. Diagnosing ICU-associated weakness can be challenging because making the diagnosis relies on volitional participation in strength testing by the patient in a very ill population that is often sedated or restrained.

This study proposes to test if bedside ultrasound of tibialis anterior (a non-invasive test that doesn't require active participation by the patient) correlates with clinical whole-body weakness in critically ill patients admitted to an ICU with sepsis.

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).

Eligibility Criteria:
Inclusion Criteria:

1. adult patients (age \> 18 years);
2. admitted to the ICU with a diagnosis of sepsis, and;
3. an ICU duration of stay of greater than 4 days (two allow for serial assessments of muscle strength and size).

Exclusion Criteria:

1. Any pre-existing diagnosis that would reasonably impact a participant's muscle bulk, strength, coordination, or ability to participate in the assessment

   * Critical illness myopathy, critical illness neuropathy, and critical illness polyneuropathy diagnosed in the current ICU stay are not to be considered exclusion criteria as these diagnoses are directly related to the research question
   * Delirium is not considered an exclusion criteria for this study so long as at least two strength assessments can be performed during the course of the participant's ICU stay.
2. Any activity orders or movement restrictions (including medical devices such as casts or external fixation devices) that would preclude accurate motor strength assessment.
3. Dressings, casts, or medical implements that would preclude or impede ultrasound assessment of tibialis anterior muscle cross-sectional area in both legs.
4. Patients who are "proned" or in positions that make assessing tibialis anterior with ultrasound or physical exam impractical.
5. Re-admission to ICU within the same hospital stay.