Critical Illness Weakness Outside the Intensive Care Unit. A Prospective Cohort Study.

When people become seriously ill, their bodies can be affected in many ways beyond the original disease. One well-known complication in patients treated in intensive care units (ICUs) is the development of severe muscle weakness caused by damage to muscles and nerves. This condition is called critical illness-related weakness and includes disorders of the nerves (neuropathy), the muscles (myopathy), or both. These problems can make it difficult for patients to move, walk, or even breathe independently, and recovery can take months or longer.

So far, most research on this type of weakness has focused on patients who were treated in ICUs. However, many hospitalized patients outside the ICU-such as those admitted to internal medicine wards or semi-intensive care units-can also experience severe infections, organ failure, inflammation, prolonged bed rest, and metabolic stress. These are the same risk factors known to cause nerve and muscle damage in ICU patients. Despite this, weakness occurring outside the ICU is often overlooked, attributed simply to "deconditioning" or prolonged bed rest, and not properly investigated.

The CRI-WEAK-OUT study aims to better understand whether critical illness-related weakness also occurs in hospitalized patients who are not admitted to the ICU, how often it happens, how severe it is, and what factors increase the risk of developing it.

This is a prospective observational study, meaning that patients will be followed over time during and after their hospital stay, without changing their usual medical care. The study will include about 600 adult patients hospitalized for acute illnesses in non-ICU wards across several Italian hospitals. Half of the participants will have signs of organ failure during hospitalization, while the other half will serve as a comparison group without organ failure.

All participants will undergo careful clinical evaluations shortly after hospital admission and again before discharge. Doctors will assess muscle strength, level of disability, independence in daily activities, and overall frailty using standardized and widely accepted scales. Six months after discharge, patients will be contacted by phone to evaluate their recovery and quality of life.

If a patient develops new or worsening muscle weakness during hospitalization, more detailed tests will be performed. These include electrical tests of nerves and muscles to understand whether the weakness is caused mainly by nerve damage, muscle damage, or both. In a subgroup of patients, additional blood samples will be collected to measure substances linked to inflammation and nerve injury. These biological markers may help doctors recognize the condition earlier and predict recovery.

By collecting detailed clinical, electrical, and biological information, the study aims to answer several important questions:

• How common is critical illness-related weakness outside the ICU?
• Which patients are most at risk?
• How does this condition affect recovery and long-term independence?
• Can blood markers help identify patients with nerve or muscle damage? The results of the CRI-WEAK-OUT study may improve awareness of this under-recognized condition, promote earlier diagnosis, and help clinicians plan better prevention and rehabilitation strategies. Ultimately, this research could lead to improved care, faster recovery, and better quality of life for many hospitalized patients who currently experience unexplained weakness after acute illness.