Associations between muscle-related cytokines and selected patient outcomes in the ICU

Systemic cytokines produced by contracting skeletal muscles may affect the onset and severity of intensive care unit (ICU)-acquired weakness after critical illness.

The purpose of this research was to determine the serum levels of interleukin (IL)-8, IL-15, and tumor necrosis factor-α (TNF-α) among patients receiving mechanical ventilation for >48 hr and examine the relationships of these myokines to outcomes of patient delirium, muscle strength, activities of daily living (ADLs), duration of mechanical ventilation, and length of ICU stay.

In this exploratory, repeated-measures interventional study, the 36 participants received 20 min of once-daily in-bed or out-of-bed activity using an established early progressive mobility protocol after physiologic stability had been demonstrated for >4 hr in the ICU. Blood samples were drawn on 3 consecutive days, beginning on the day of study enrollment, for serum cytokine quantification.

IL-8, IL-15, and TNF-α were highly variable and consistently elevated in participants compared to normal healthy adults. About 1/3 of participants were positive for significant muscle weakness at discharge from ICU. Repeated values of mean postactivity IL-8 serum values were significantly associated only with ADL following ICU discharge. There were no significant associations with repeated values of mean postactivity IL-15 or TNF-α serum values and outcomes.

Results provide preliminary data for exploring the potential effects of elevated serum values IL-8 and IL-15 in muscle health and TNF-α for muscle damage, including effect sizes to calculate the sample sizes needed for future studies.