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Multiple versus single injections of fluorescent microspheres for the determination of regional organ blood flow in septic sheep

Determination of regional blood flow by the injection of microspheres in sepsis models is crucial for the experimental evaluation of the influence of experimental treatment strategies on organ perfusion. However, multiple injections may critically increase the total quantity of microspheres, thereby restricting regional microcirculation and altering the results of blood flow measurements. This study was designed to compare the results of multiple versus single injections of microspheres in an established ovine sepsis model. Injury was induced by smoke inhalation and instillation of Pseudomonas aeruginosa into the lungs. Twenty sheep were studied for 4, 8, 12, 18, or 24 h, respectively. Microspheres were injected at the end of the study period and the animals were euthanized and organ tissues were harvested. Another four sheep were studied for 24 h and multiple microsphere injections were performed at the above indicated time points in the same animals. Tracheal blood flow significantly increased and blood flow to the pancreas and ileum significantly decreased versus baseline in both groups (P < 0.05 each). Blood flow to the ileum, renal cortex and skin did not significantly change versus baseline in both groups (P > 0.05). Blood flow was higher to the trachea in the multiple injection group at 18 h (P = 0.048) and to the ileum at 12 h (P = 0.049), and lower to the skin at 18 h (P = 0.015). In conclusion, the results indicate that multiple versus single microsphere injections induced no or negligible alterations during ovine sepsis. This finding may help reduce the quantity of animals needed in future experiments.