Reduced red blood cell deformability over time is associated with a poor outcome in septic patients

Background: To investigate changes in red blood cell (RBC) rheology over time in critically ill patients with sepsis and their relationship with outcome. Methods: In this prospective, non-interventional study, RBC rheology was assessed using the Laser-assisted Optical Rotational Cell Analyzer in a convenience sample of intensive care unit (ICU) patients with (n = 64) and without (n = 160) sepsis. Results were compared to measures in healthy volunteers (n = 20). RBC rheology was also assessed on days 1 and 3 of the ICU stay in 32 of the non-septic and 19 of the septic patients. RBC deformability was determined by the elongation index (El) in relation to the shear stress (0.3 to 50 Pa) applied to the RBC membrane. An aggregation index (AI) was assessed simultaneously with the same device. Results: The ICU mortality rate of the septic patients was 31%. RBC deformability was already reduced in septic patients at ICU admission, an effect that persisted during the study period and worsened in the non-survivors for the large majority of shear stresses studied (e.g., El for 50 Pa of shear stress was 0.527 +/- 0.064 in non-survivors vs. 0.566 +/- 0.034 in survivors, p < 0.05). These changes were not observed in non-septic patients. The AI was more elevated in septic than in non-septic patients at ICU admission, but had no prognostic value. Conclusions: Alterations in RBC rheology, including reduced deformability and increased aggregation, occur early in septic patients and reductions in RBC deformability over time are associated with a poor outcome.