Clinical relevance of platelet function testing in cardiac surgery

Bleeding therapy with platelet (PLT) concentrates is routinely guided by the PLT count (PLT-C). However, doubts are increasing as to the suitability of the PLT-C for reflection of the haemostatic PLT capacity. We used cardiac surgery as a model to compare PLT-C with function (PLT-F).

Impedance aggregometry (Multiplate®, TRAPtest) was used to assess PLT function in 3.212 cardiac surgery patients. Thrombin receptor activating peptide (TRAP) together with PLT count was assessed sequentially at incision (start, "S") and before administration of protamine ("bP"), as well as during haemostasis after protamine application ("aP"). Subgroup analyses comprised both surgery type as well as comparison of bypass surgery with or without heart lung machine (HLM). Red blood cell concentrate (RBC) transfusion needs during the intra-operative and 24hrs postoperative period were put into relation with aggregation findings.

The relation from "S" to "bP" shows the PLT count to decrease in 83.8% of patients whereas aggregation capacity (TRAP) increases in 55.6% of patients. This mobilisation of PLT function is strongly and rapidly reversible in 68.0% of patients with aggregation values dropping below the values at "S". Significant differences in aggregation dynamics are found with respect to the type of surgery. Unexpectedly, HLM induced decrease of platelet function is moderate and observed only after departure from the extracorporeal circulation (p<0.001), but not at "bP" (p>0.05). RBC transfusion volumes are correlated inversely with aggregation capacities and dynamics independently from PLT counts. Notably this is true even for the PLT-F at "S".

PLT haemostasis as judged by aggregometry deviates from PLT count. Aggregometry allows for inter-individual as well as surgery type-specific distinction of PLT function. HLM induced loss of platelet function is delayed until departure from the HLM. According to an inverse correlation of aggregometry with RBC transfusion, PLT function predicts bleeding intensity. PLT transfusion tailored by aggregometric testing may allow for optimisation of intra-operative patient blood management.

There is no conflict of interest.