The problem of analysis of clinical - diagnostic and biochemical criteria of postoperative cognitive dysfunction in abdominal oncosurgery, depending on the degree and structure of disorders, remains unresolved, which determines its relevance. The role of 2, 3-diphosphoglycerate is essential, because its increase in the concentration of red blood cells in hypoxic conditions is one of the adaptive mechanisms that improve oxygen transport to tissues. Purpose. The influence of the dynamics of 2,3 diphosphoglycerate content, as the main indicator of hypoxia, on the occurrence of cognitive dysfunction in the postoperative period in patients with neoplasms of the abdominal cavity. The study was conducted on the basis of departments for patients of the surgical profile of the municipal institution "Kharkiv City Clinical Hospital of Ambulance and Emergency Care named after Professor OI Meshchaninov ". To achieve this goal, we examined 80 patients with abdominal neoplasms who underwent surgery under general anesthesia using propofol and fentanyl. All patients were divided into 2 groups depending on the age of patients on the WHO scale, who underwent surgery using general anesthesia: Group 1 (n = 39) - middle-aged patients (50-59 years); Group 2 (n = 41) - elderly and senile patients (60-80 years). The control points of the examination were the day before the operation and the 1st, 7th, 30th day from the moment of the operation. The state of cognitive function in these patients was determined by conducting neuropsychological tests. To assess the state of cognitive function of patients, neuropsychological tests were used: MMSE scale (Mini-Mental State Examination, MMSE), the method of memorizing 10 words AR Luria, frontal dysfunction battery (FAB), Schulte technique. To assess the state of energy metabolism in patients, the level of erythrocytes and hemoglobin in the blood analysis was determined by well-known methods, the level of 2,3 diphosphoglycerate in erythrocytes and its ratio to hemoglobin. Anemia in the first week after surgery in patients of group 1 contributes to the development of a hypoxic state, in erythrocytes there is an increase in the content of 2,3 41 diphosphoglycerate, which promotes the transport of oxygen to tissues. During the week there is an increase in the intensity of the formation of 2,3 diphosphoglycerate, as evidenced by the ratio of 2,3 diphosphoglycerate to hemoglobin. In patients of group 2, the changes are more pronounced: anemia with a significant decrease in erythrocytes and hemoglobin in the blood, a decrease in 2.3 diphosphoglycerate in erythrocytes, reflects changes in erythrocyte metabolism, namely a decrease in biosynthesis of important organophosphorus compounds, in particular 2,3 diphosphogly by reducing the basic enzymes of glycolysis. Decreased energy metabolism in the elderly contributes to impaired cell function. With age, the content of adenosine triphosphate, 2,3 diphosphoglycerate decreases, thus increasing the affinity of hemoglobin for oxygen, impaired transport of oxygen to tissues, which leads to the development of hypoxia. According to the results of neuropsychological tests, we found postoperative cognitive dysfunction in patients with neoplasms of the abdominal cavity. Disruption of energy metabolism and changes in the activity of glycolysis enzymes in erythrocytes contributes to a decrease in the concentration of 2, 3 diphosphoglycerate, increase the affinity of hemoglobin for oxygen and the development of tissue hypoxia. The obtained results indicate the interdependence of these processes and allow continuing research in this direction with the development of appropriate clinical and diagnostic measures and areas of intensive care to improve the condition of patients with abdominal tumors and their quality of life after surgery.