A defined period of sensitivity of an experimental burn wound to a second injury

We sought to determine whether the zone of stasis of an experimental burn exhibits a defined period of sensitivity to a sublethal exposure to ischemia. A standard burn injury was inflicted on the abdominal skin of rats consisting of two burn areas separated by a 5-mm strip corresponding to the zone of stasis. Either immediately or after a delay of 24, 48, or 72 hours, the area of the burn and interspace was elevated as a flap based on the inferior epigastric vessels and subjected to a 5-hour period of ischemia that in itself is insufficient to cause necrosis. Forty-eight hours later, the flap was harvested to assess the viability of the panniculus; carnosus. Necrosis of the panniculus in the interspace was not seen in any animal where burn was not subjected to ischemia (n = 6) or in any flap subjected to a 5-hour period of ischemia immediately (less than 30 minutes) after the burn (n = 7). In contrast, when the period of ischemia was delayed 24 hours after the burn, necrosis of the muscle in the interspace was seen in 5 out of 6 flaps (P = .0047), as it was in rats in which the start of ischemia was delayed 48 hours (n = 2). However, this effect was abolished with a delay of 72 hours (n = 2). These findings show that the zone of stasis displays increased sensitivity to ischemia 24 to 48 hours after burning. Thus, sequential subnecrotic injuries can have a cumulative effect, but a delay between the two is required.