Figure 2. Exposure to CPB resulted in mild platelet activation.

WB was recovered from neonates at four times during CPB surgery, including prior to initiation of surgery (Baseline; circles), after completion of surgery but before separation from CPB (On CPB; triangles), after separation from CPB and prophylactic transfusion of platelets (Post CPB; diamonds), and immediately after admission to the cardiac intensive care unit (CICU; squares). Activated platelets were identified by flow cytometry following staining with a phycoerythrin (PE)-tagged antibody specific for the platelet α-granule constituent, P-selectin. Results are reported as (A) the percentage of platelets that were PE positive and (B) PE median fluorescence intensity (MFI). Each symbol represents the result for a single patient, bars denote means ± standard deviations, and dotted lines represent 0 percent PE-positivity (A) or PE MFI = 0 (B). Generalized Estimating Equation (GEE) with maximum likelihood estimation method was used to model the variables over time accounting for bleeding status. Lognormal distribution with identity link function was used for comparisons. Statistically significant differences between groups are indicated by p values. Note that, while the percentage of platelets that were P-selectin positive was significantly greater On CPB relative to Baseline, the MFI of P-selectin-positive platelets was, albeit significantly, only slightly greater than Baseline at the On CPB and Post CPB time points. (n=42 - patient 26 excluded for technical reasons and patient 38 excluded because of high Baseline PE MFI)