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SYNOPSIS Blood coagulation tests were performed on admission to the hospital and on consecutive days after severe and moderate head injury in 34 patients. Platelet counts and fibrinogen were normal at admission and raised thereafter. The partial thromboplastin time was shortened at admission and lengthened in the following days. Fibrinolytic activity was enhanced at admission. The ethanol gelation test was negative in all patients during the post-traumatic time course. It was concluded that, in the first 24 hours after injury, activated coagulation was present after head injury. In contrast with data of other authors, disseminated intravascular coagulation did not occur in these series.

SYNOPSIS ADP-induced platelet aggregation was studied for up to six weeks in 34 patients with head injuries. The patients were divided into three groups according to the degree of impaired consciousness assessed by a clinical coma scale, and change in platelet aggregation was related to the coma score. Platelet aggregation was markedly reduced in all eight patients dying within 24 hours of injury. All 17 patients who remained unconscious for four days or more showed decreased platelet aggregation up to nine days after admission, the most marked effect being on the second day. Platelet function in this group returned to normal within 16 days. Nine patients with only slightly impaired consciousness also showed subnormal platelet aggregation during the first few days with a return to normal by the fourth day. Platelet counts remained within normal limits in all groups. We suggest that during coma following head injury brainstem dysfunction induces neurohumoral changes in the blood which are responsible for a decrease in platelet function.Several recent reports (Goodnight et al, 1974;Preston et al, 1974), have described coagulation abnormalities in relation to head trauma. In these studies platelet counts were done but no attention was given to platelet function. Platelet abnormalities are found in other neurological diseases; after cerebrovascular accidents decreased platelet aggregation has been described (Danta, 1973), and multiple sclerosis is associated with enhanced platelet stickiness (Caspary et al, 1965). In Down's syndrome platelet serotonin (5HT) uptake is found to be decreased (Bayer and McCoy, 1974). Functional disorders of the neutrophil granulocyte (which in several aspects is similar to the blood platelet (Stormorken, 1969)) are found after brain damage, anoxia (Dodsworth and Harris, 1971), and head injury (Van Woerkom et al, 1973). During general anaesthesia impaired phagocytosis is recognized (Lofstrom and Schildt, 1974) and during operations impaired platelet aggregability, possibly caused by general anaesthesia, has been described (O'Brien et al, 1971). In these conditions the changes in platelet and leucocyte function seem to be related to the state of consciousness. Therefore we aimed to study platelet function after severe head injury, particularly in relation to the degree of impaired con-

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