Platelet-monocyte pro-coagulant interactions in on-pump coronary surgery.

OBJECTIVE: Platelets and monocytes possess haemostatic properties, but the clinical effect of platelet-monocyte interactions on haemostasis following coronary surgery is not known. The study characterises the platelet and monocyte responses in cardiac surgery and its impact on haemostasis. METHODS: In 1342 patients, changes in white blood cell counts (WBC), monocyte counts and platelet counts were measured. PMC formation was analysed by flow-cytometry using monoclonal antibodies against pan-leucocyte marker CD45, monocyte marker CD14 and platelet marker CD42. TF expression was determined using monoclonal antibodies against, CD45, CD14 and human-TF. Continuous variables were expressed as mean+/-SD. Changes in monocyte and platelet counts over time were considered as repeated measures data, and analysed using Generalised Estimating Equations (GEE). Multivariate regression analysis was used to evaluate the effect of several factors on blood loss. RESULTS: A monocytosis occurs with on-pump coronary surgery, but is less pronounced than with off-pump surgery. No difference was seen in patients having redo-surgery or more complex cardiac surgery. Factors associated with monocytosis on multivariate analysis were higher body mass index (p=0.02), diabetes (p=0.035) and smoking (p=0.01). Older patients manifested a lower response (p<0.001). Cross-clamp fibrillation was associated with a lower (p=0.048) monocytic response than was cardioplegia. PMC formation dropped following administration of heparin, peaked at 5 min of CPB, and declined by 2h of CPB (p=0.04). A return towards preoperative levels was found during postoperative days 1-5. No significant change in monocyte TF expression occurred. The mean postoperative blood loss was 581.2+/-292.8 ml, and inversely related to increasing preoperative platelet counts (p<0.001), and to higher monocyte % counts (p=0.012). Patients, who were female (p<0.001), had higher body mass indices (p<0.001), and higher core body temperatures during surgery (p=0.013), as well as patients having perioperative aprotinin (p<0.001) related to less blood loss. CONCLUSIONS: A higher postoperative platelet count as well as monocyte% significantly and independently decreases postoperative blood loss following cardiac surgery.