Platelet size and mass as an indicator for platelet transfusion after cardiopulmonary bypass

Platelet count, mean platelet volume (MPV), and plateletcrit (PCT) were studied in 51 patients after cardiopulmonary bypass (CPB). MPV was significantly lower in 10 patients who developed postoperative bleeding (bleeders) compared to 41 with no significant bleeding (nonbleeders) (7.7 ± 0.86 vs 8.5 ± 1.2 f1, p < .05). Postoperative platelet count was significantly lower in the group of bleeders (93.3 ± 22.4 vs 127.5 ± 43 x 10⁹/liters, p < .02). A cutoff point of MPV or platelet count that would include bleeders and exclude nonbleeders could not be found due to the large overlap between the two groups. However, such a cutoff point does exist for PCT (PCT = total platelet mass). PCT was significantly lower among the bleeders (0.072 ± 0.02% vs 0.108 ± 0.036%, p < .05) and a cutoff point of PCT less than 0.1% included all the bleeders and excluded 65% of nonbleeders. The low PCT and bleeding tendency can be corrected by platelets transfusion. In 15 patients (eight bleeders and seven nonbleeders) with low postoperative PCT (0.078 ± 0.014), transfusion of 10 platelet units increased platelet count from 101 ± 32 to 169 ± 22 x 10⁹/liter, increased PCT to 0.128 ± 0.2%, and stopped bleeding in all bleeders. A finding of PCT less than 0.1% after CPB is a clear indication for platelet transfusion in patients who develop post-CPB bleeding. This supports the observation that large platelets are more active than smaller ones, and that PCT, rather than PLT counts, predicts the risk of bleeding in patients with thrombocytopenia.