Timing Relationships for Secondary Ischemia in Rodents: The Effect of Arteriovenous Obstruction

ABSTRACT The first ischemic insult a tissue suffers is primary (1°) ischemia. A second ischemic episode, such as thrombosis after free tissue transfer, may be regarded as secondary (2°) ischemia. Timing relationships were studied in a rodent epigastric-flap model. In a first experiment, the interval between 1° ischemia and 2° ischemia was varied. Flaps which had 2° ischemia 12 and 36 hr after the 1° episode, had decreased ischemic tolerance, compared with 1° ischemic flaps; 2° ischemic flaps, after an interval of 72 hr, had an ischemic tolerance similar to 1° ischemic flaps. In a second experiment, the length of the 1° ischemia was varied. It was found that as little as 5 min of 1° ischemia significantly decreased the subsequent tolerance of 2° ischemia. The possible clinical significance of these results is discussed.