Microdialysis detection of lactate in subcutaneous tissue as a reliable indicator of tissue metabolic disorders in an animal sepsis model.

PURPOSE: Tissue dysoxia is thought to be a fundamental cause of the organ failure that occurs as a result of shock. Plasma lactate has been frequently measured as an indicator of the state of systemic tissue metabolism. On the other hand, tissue lactate levels can directly indicate a disorder in the state of cytological tissue metabolism. The continuous monitoring of lactate levels in subcutaneous tissue will reflect the state of tissue dysoxia more precisely than levels of lactate in the plasma lactate. We have investigated the differences in the levels of plasma and tissue lactate using a microdialysis (MD) technique in an animal septic shock model.

METHOD: Male 8-week-old Wistar/ST rats were used. We prepared an animal model by injection of lipopolysaccharide (LPS) into the abdominal cavity. LPS was given to 9 animals in the experimental group while physiological saline was given to 6 animals in the control group. A MD probe was used to quantify the lactate levels in the subcutaneous tissue. The mean arterial pressure, blood gas content and lactate levels were measured every 50 min up to 400 min after injection and compared between both groups.

RESULT: The MAP of both groups showed similar changes after injection. Plasma lactate levels in the LPS group showed a significant increase after 100 min and reached a plateau from 150 min to 250 min. Subcutaneous lactate in the LPS group showed a significant increase after 150 min. Subcutaneous pyruvate in the LPS group showed a significant increase after 100 min. The lactate/pyruvate (L/P) ratio in the subcutaneous tissue showed a sustained increase from 300 min in the LPS group.

CONCLUSION: Monitoring plasma lactate levels is useful for the early assessment of anaerobic metabolism before hypotension. Plasma lactate levels did not increase during some periods. This phenomenon was due to the balance between production and utilization. However, tissue lactate showed a chronological increase. These results suggest that the measurement of tissue lactate levels is reliable for assessing local energy metabolic disturbances. Under conditions of septic shock, an increase in lactate levels was found to be a sensitive marker of tissue metabolism disorder.