Utility of microdialysis to detect the lactate/pyruvate ratio in subcutaneous tissue for the reliable monitoring of hemorrhagic shock

The present experiments were carried out to investigate the usefulness of measuring peripheral tissue metabolism for the clinical assessment of shock. Male Wistar/ST rats (8 weeks-old) were used. All rats were placed in a supine position while anesthetized. A tube for measuring arterial pressure and collecting blood samples was cannulated into the femoral artery. For microdialysis, the introducer was inserted into the subcutaneous tissue in the abdominal wall. Blood was exsanguinated to maintain the mean arterial pressure at 40 +/- 5 mmHg. Mean arterial pressure, arterial blood gas and serum lactate levels were measured. Microdialysis was performed to quantify the levels of lactate and pyruvate in the subcutaneous tissue. Six rats died due to hemorrhagic shock by 350 min (Group D) while six rats had survived for the 350 min period after exsanguination (Group A). These data was obtained at intervals of 50 min after exsanguination up to a period of 250 min and compared between Groups A and D. In Group A, serum lactate levels did not increase throughout the entire period of observation. Serum lactate levels in Group D transiently increased, but did not show a dramatic increase during the blood pressure maintenance period. In particular, serum lactate levels increased again after a period of more than 150 min following exsanguination. Lactate levels in the subcutaneous tissue gradually increased and were significantly higher in Group D than that in Group A after 150 min. The L/P ratio in Group A remained fairly constant during the period of observation. In contrast, the L/P ratio in Group D increased gradually, and was significantly higher than that in Group A after 100 min. It was concluded that the continuous increase in the L/P ratio in the subcutaneous tissue in Group D was indicative of tissue circulatory failure and of an abnormality in tissue oxygen metabolism prior to the detection of the collapse of compensatory mechanisms appearing in the vital signs. These findings suggest that measuring the L/P ratio is useful for the clinical assessment and monitoring of shock.