Objective:To study difference in arterial oxygen(PO 2) pressure between the carotid artery and the femoral artery and its relation with hypoxia of brain after head injury.Methods:Forty patients with acute head injury were divided into four groups according to the GCS(Ⅰ:6 patients for GCS 3-5score;Ⅱ:16 patients for GCS 6-8 score;Ⅲ:8 patients for GCS 9-12 score;Ⅳ:10 patients for GCS 13-15score).The PO 2 of the carotid artery and the femoral artery was monitored for every patient.At the same time

26 patients from all groups were monitored using transcranial dopplergraphy.Additional

22 patients with severe head injury were continuously monitored on PO 2 of the carotid artery and the femoral artery for 5 days.Results:(1)The difference in PO 2 between the carotid artery and the femoral artery was identified in Ⅰ and Ⅱ groups.The PO 2 of carotid artery is much less than that of femoral artery(P<0.05).(2)When the PO 2 of carotid artery with severe head injury was reduced persistently during the first 5 days after admission

the prognosis of patients must be poor.(3)The changes of the difference in PO 2 between the carotid artery and the femoral artery correlated with the diastolic velocity of middle cerebral artery and the GCS.Conclusion:With the increase of ICP after head injury

the difference in PO 2 between the carotid and the femoral increases gradually.Therefore we suggest that the oxygen in short supply is one of the most important reasons for hypoxia of brain tissue.