Our study compared the effect of CPB on platelet function by using pre-and intra-operative platelets function parameters for 34 patients using PFA-100 analyzer and MEA. Data for two patients were removed due to erroneous PFA-100 values leading to 32 patients' data used for this study. Although all patients going for CPB procedure were advised to stop antiplatelet therapy five days prior to the procedure, we found 7 patients presenting with high PFA-100, suggesting some residual effect of antiplatelet.
Out of 32 patients, 9 (28.1%) were females with a mean age of 53.1 ± 15.4 (m: 52, r: 30–73 years), and 23 (71.9%) were male with a mean age of 58.9 ± 8.75 (m: 59, r: 40–79 years), where 'm' denotes the median, and 'r' denotes range.
We presumed that pre- and intra-operative measurements should show significant change towards worsening of platelet function. Pre-and intra-operative PFA-100, MEA and CBC measurements are summarized in Table-1. The variables showing greatest pre and intra-op variability are depicted as a Box Whisker plot in Figure-1, where one set depicts both PFA- ADP and epinephrine (EPI), and other shows only MEA-ADP and RISTO. The ADP observations for pre-and intra-op are 32 and 31 respectively, with an increase in mean values from 125.9 ± 69.9 (m: 102, r: 54–300 sec) to 205 ± 74.9 (m: 162, r:79–300). The EPI measurements also showed an increase in mean values from 166.8 ± 72.5 (m: 187, r: 64–300) to 214.2 ± 42.7 (m: 210, r: 115–300). This increase clearly shows worsening of platelet function. The significance of platelet function change is estimated using student t-test, both ADP and EPI show significant difference P–values < 0.001 and 0.002, respectively.
Table-1 also summarizes MEA measurements. Overall, the tests show a decline in the measurements consistent with a decline in the aggregation(17). A significant decline (P-value < 0.001) in mean and median values of ADP (AUC) is observed from 81.5 ± 28.3 (m: 75.5, r: 26–124) to 56.8 ± 27.4 (m: 53.5, r: 7–39 AUC*min; a 30% decrease). A decline in ASP was insignificant (P–value 0.085) in mean and median values from 59.2 ± 27.6 (m: 56.5, r: 23–122) to 50.2 ± 30.8 (m: 48.5, r: 10–112 AUC*min; a 14% decrease). A decrease in COL was significant (P–value 0.002) in mean and median values from 50 ± 19 (m: 43.5, r: 27–97) to 37.1 ± 18.1 (m: 35; r: 4–80 AUC*min; a 24.5% decrease). Similarly, a significant decline was observed in RISTO and TRAP mean and median values (P–value 0.0005 and 0.02, respectively). RISTO decreased from 76.8 ± 30.9 (m: 72.5, r: 33–156 AUC*min) to 50.9 ± 37.9 (m: 41, r:4–181 AUC*min; a 33.7% decrease). TRAP declined from 114 ± 26.3 (m: 112, r: 51–178) to 100 ± 36 (m: 95, r: 13–179 AUC*min, a 3.5% decrease). This little change in TRAP indicates that the sample is not contaminated with antiplatelets (14).
A significant drop in Hb values was also observed one hour after the start of CPB (P–value < 0.001) from 137 ± 12.5 (m: 11.6, r: 71–157) to 8.43 ± 1.24 (m: 8.3, r: 9–108 g/L, a 26% decrease); HCT (P–value < 0.001) from 34.5 ± 5.5 (m: 34.2, r: 23.4–46.7) to 25 ± 2.6 (m: 24.5, r:20.6–29.7; a 27.5% decrease); PLT (P–value < 0.001) from 264 ± 131.9 (m: 255) to 185.3 ± 112.6 (m: 164).
Next, we tried to answer if PFA-100 pre-op values related to intra-op drop in Hb value, as in, do we expect lower Hb count for elevated PFA-100 values. We assumed two approaches to find the answer: first, we look for a correlation between PFA-100 variables and intra-op Hb; secondly, we run a statistical t-test which shows a significant change in Hb groups based on a dichotomy of PFA-100 variables. The binary variable was labelled 'abnormal' when both ADP and EPI values exceeded the normal range and labelled 'normal' otherwise.
We used Pearson's correlation and found a weak correlation coefficient between PFA-ADP and intra-op drop in Hb (0.4699), which is illustrated as a scatter plot in Figure-2. On the other hand, pre-op EPI showed no correlation (0.21) with the drop in intra-op Hb values, as illustrated in Figure-3. For t-test, we created a binary variable based on the values of PFA-ADP and EPI. Next, we partitioned the post-op drop in Hb based on this binary variable and compared their means using t-test. The number of patients in the abnormal set was 6, and 26 in the normal set. The difference of mean turned out to be significant (P–value 0.01), and Hb mean values for abnormal set 75 ± 0.5 (m: 75, r:69–82) were lower than that of the normal set 86 ± 1.02 (m:87, r:71–108). An observation worth mentioning is that for MEA test, only pre-op RISTO and TRAP showed a weak inverse correlation with the intra-op drop in Hb (-0.31 and − 0.36), while rest of the MEA variables didn't.
Another perspective was to look at the change in intra-op PFA-100 and MEA values against a drop in intra-op Hb. Change in intra-op PFA-100 and MEA values were obtained by subtracting intra-op from pre-op values. Similarly, the drop in intra-op Hb value was obtained by subtracting intra-op Hb from pre-op Hb. For PFA-100, change in intra-op ADP was weakly correlated to the drop in intra-op Hb (0.46). For MEA, intra-op change in ASP was weakly correlated to the drop in intra-op Hb (0.41).
Considering the gender, mean Hb levels in female patients 75 ± 0.5 (m: 73, r: 69–84 g/L) were significantly lower (a 16% decrease, P–value 0.0009) than the male patients 87 ± 1.0 (m: 87, r: 71–108 g/L). The same pattern was observed in HCT levels.