No association between systemic complement activation and intensive care unit-acquired weakness

Background: The main risk factors for intensive care unit-acquired weakness (ICU-AW) are sepsis, the systemic inflammatory response syndrome (SIRS) and multiple organ dysfunction. These risk factors are associated with systemic complement activation. We hypothesized that critically ill patients who develop ICU-AW have increased systemic complement activation compared to critically ill patients who do not develop ICU-AW.

Methods: Complement activation products C3b/c, C4b/c and C5a were measured in plasma of ICU patients with mechanical ventilation for ≥48 hours. Samples were collected at admission to the ICU and for 6 consecutive days. ICU-AW was defined by a mean Medical Research Council (MRC) score <4. We compared the level of complement activation products between patients who did and who did not develop ICU-AW.

Results: Muscle strength measurements and complement assays were available in 27 ICU patients, of whom 13 patients developed ICU-AW. Increased levels of C4b/c were seen in all patients. Neither admission levels, nor maximum, minimum and mean levels of complement activation products were different between patients who did and did not develop ICU-AW.

Conclusions: Complement activation is seen in critically ill patients, but is not different between patients who did and who did not develop ICU-AW.