In-vivo and real-time ultrasonic monitoring of red blood cell aggregation with the structure factor size and attenuation estimator during and after cardiopulmonary bypass surgery in swine

Cardiopulmonary bypass (CPB) used during cardiac surgery induces a systemic inflammatory response. The severity of that response has been shown to be proportional to patient outcome. Markers of inflammation are typically obtained intermittently through blood testing with variable delay. Red blood cell (RBC) aggregation is a surrogate marker of inflammation that can be quantified with ultrasound. It could therefore represent a real-time inflammation monitoring instrument for patient care. However, the relationship between markers of inflammation during CPB and RBC aggregation is unknown. Seven swine underwent a 90 min procedure with CPB followed by a 120 min reperfusion. To induce a more severe inflammatory reaction, lipopolysaccharide (LPS) was administrated 24 h prior to surgery and just before the CPB in 4 pigs (LPS group). Other pigs composed the control group (CONT group, n=3). A RBC aggregation parameter was extracted from ultrasonic images acquired over the femoral vein. The mean fractal size of aggregates (D), which was determined with the Structure Factor Size and Attenuation Estimator (SFSAE), was calculated. Measurements were performed at the beginning (T_CPB15), after 30 min. (T_CPB30) and at the end (T_CPB90) of CPB. Measurements were repeated during reperfusion after 30 and 120 min of recirculation (T_REP30 and T_REP120). The temporal evolution of interleukin 6 (IL-6), a blood inflammatory marker, was also assessed. D exhibited a significant increase from T_CPB30 to T_REP120 in all swine, matching IL-6 evolution. The LPS group presented significantly higher RBC aggregation during the reperfusion compared with control pigs, which indicates potentially high sensitivity of the SFSAE. This new cellular imaging modality may become a real-time non-invasive monitoring technique to anticipate inflammation-related complications during high-risk surgery or sepsis situation.