Near-patient coagulation testing to predict bleeding after cardiac surgery: a cohort study

Higher body mass index raises immature platelet count: potential contribution to obesity-related thrombosis

Higher body mass index (BMI) is a risk factor for thrombosis. Platelets are essential for hemostasis but contribute to thrombosis when activated pathologically. We hypothesized that higher BMI leads to changes in platelet characteristics, thereby increasing thrombotic risk. The effect of BMI on platelet traits (measured by Sysmex) was explored in 33 388 UK blood donors (INTERVAL study). Linear regression showed that higher BMI was positively associated with greater plateletcrit (PCT), platelet count (PLT), immature platelet count (IPC), and side fluorescence (SFL, a measure of mRNA content used to derive IPC). Mendelian randomization (MR), applied to estimate a causal effect with BMI proxied by a genetic risk score, provided causal estimates for a positive effect of BMI on both SFL and IPC, but there was little evidence for a causal effect of BMI on PCT or PLT. Follow-up analyses explored the functional relevance of platelet characteristics in a pre-operative cardiac cohort (COPTIC). Linear regression provided observational evidence for a positive association between IPC and agonist-induced whole blood platelet aggregation. Results indicate that higher BMI raises the number of immature platelets, which is associated with greater whole blood platelet aggregation in a cardiac cohort. Higher IPC could therefore contribute to obesity-related thrombosis.

Viscoelastic testing in cardiac surgery

Bleeding complications are common in cardiac surgery and lead to an increase in morbidity and mortality. This is multifactorial in aetiology including the effects of cardiopulmonary bypass, the drugs given to manipulate the coagulation system and the vascular nature of the surgery itself. Viscoelastic tests provide a point of care, rapid assessment of coagulation which offer the advantage of faster turnaround times and a nuanced view of the elements of the coagulation system allowing targeted therapy to be delivered quickly. Both thomboelastography (TEG)and thromboelastometry (ROTEM) have been recommended for use in cardiac surgery, both have shown a reduction in transfusion and bleeding when used as part of a testing algorithm. They are particularly useful in assessing residual heparinisation and fibrinogen levels. Additionally, TEG allows the evaluation of the effects of anti-platelet agents on platelet function. This review discusses the mechanisms by which bleeding occurs in cardiac surgery and explores three uses of viscoelastic testing in cardiac surgery: to predict bleeding, to assess platelet function and peri-operative testing to reduce transfusion.