Critical Care Medicine www.ccmjournal.org e171 Objectives: In many pathological conditions, including high-risk sur-

gery, the severity of the inflammatory response is related to the patient outcome. However, determining the patient inflammatory state pres-ents difficulties, as markers are obtained intermittently through blood testing with long delay. RBC aggregation is a surrogate marker of inflammation that can be quantified with the ultrasound Structure Factor Size and Attenuation Estimator. The latter is proposed as a real-time inflammation monitoring technique for patient care. Design: Ten swine underwent a 90-minute cardiopulmonary bypass, and surveillance was maintained during 120 minutes in the postbypass period. To promote the inflammatory reaction, lipo-polysaccharide was administrated two times prior to surgery in six of those swine (lipopolysaccharide group). During the whole procedure, the Structure Factor Size and Attenuation Estimator cellular imaging method displayed a RBC aggregation index (W) computed from images acquired within the pump circuit and the femoral vein. Interleukin-6, interleukin-10, C-reactive protein, hap-toglobin, immunoglobulin G, and fibrinogen concentrations were measured at specific periods. Main Results: Compared with controls, the lipopolysaccharide group exhibited higher W within the pump circuit (p < 0.05). In the femoral vein, W was gradually amplified in the lipopolysaccharide group during cardiopulmonary bypass and the postbypass period (p < 0.05), whereas interleukin levels were higher in the lipopoly-saccharide group but only at the end of cardiopulmonary bypass and beginning of postbypass (p < 0.05). Conclusions: Continuous RBC aggregation monitoring can char-acterize the evolving inflammatory response during and after car-diopulmonary bypass. The Structure Factor Size and Attenuation Estimator is proposed as a real-time noninvasive monitoring tech-nique to anticipate inflammation-related complications during high-risk surgery or critical care situations. Because RBC aggre-gation promotes vascular resistance and thrombosis, W could also provide early information on vascular disorders in those clini-cal situations. (Crit Care Med 2013; 41:e171–e178) Key Words: cardiopulmonary bypass; critical care; erythrocyt