Assessment of Ischemia-Induced Reperfusion Injury in the Pig Latissimus Dorsi Myocutaneous Flap Model

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Experiments were conducted to assess ischemia-induced reperfusion injury in the pig latissimus dorsi myocutaneous flap model. Forty Yorkshire pigs (19.5 ± 0.6 kg) were assigned to groups A, B, C, and D (n = 10 pigs). Bilateral 8 × 13 cm latissimus dorsi myocutaneous flaps were constructed in each pig, and one flap was assigned to ischemic treatment and the contralateral flap served as a nonischemic control. The treatment flaps in groups A, B, C, and D were subjected to 2, 4, 6, and 8 hours of warm global ischemia, respectively. Pigs in groups A, B, C, and D were divided into two subgroups (n = 5 pigs), and extents of skin and muscle necrosis in control and treatment flaps were assessed with the fluorescein and nitroblue tetrazolium dye stain tests, respectively, after 2 and 7 days of reperfusion. Significantly (p < 0.01) greater extents of skin and muscle necrosis were observed in latissimus dorsi myocutaneous flaps subjected to 4, 6, or 8 hours of ischemia compared with their contralateral controls. Extents of skin and muscle necrosis also increased significantly (p < 0.01) with increases in ischemia time in treatment flaps. Of particular importance was the observation that there was no significant difference in the extent of skin or muscle necrosis between 2 and 7 days of reperfusion in all control and treatment groups. This observation indicates that 2 days of reperfusion time is adequate to assess the maximum extent of skin and muscle ischemia-induced reperfusion injury in pig latissimus dorsi myocutaneous flaps. Furthermore, it was observed that 1-cm segments of latissimus dorsi muscle were not too thick to allow the use of the nitroblue tetrazolium dye stain test for assessment of muscle viability, as judged by the highly correlated (r = 0.98, n = 40) linear relationship between assessment of muscle viability from one transverse cut surface of muscle segments and by weighing total viable and nonviable muscles dissected from the flaps according to the nitroblue tetrazolium dye stain on both transverse cut surfaces. It is important to note that the maximum length of the latissimus dorsi myocutaneous flap model for ischemia-induced reperfusion injury research should not exceed the maximum length of skin viability in the nonischemic control in order to avoid the complication of skin necrosis due to excessive length of skin. The pattern of muscle necrosis revealed by nitroblue tetrazolium dye staining indicated that muscle necrosis occurred mainly and consistently in the proximal dorsal portion of the latissimus dorsi myocutaneous flap, where the muscle was the thickest, thus permitting easy access for multiple muscle biopsies without significant damage to the flap. Histologic study revealed that the pig latissimus dorsi muscle was composed of types I(19 percent) and II (81 percent) muscle fibers. There was no observable indication of difference in tolerance of ischemia-induced reperfusion injury between these two types of fibers because the nitroblue tetrazolium dye stain was quite uniform in the viable and nonviable areas of the latissimus dorsi muscle. The technical information obtained from the present experiments is important when using the pig latissimus dorsi myocutaneous flap model to study the pathophysiology and pharmacology of ischemia-induced reperfusion injury in myocutaneous flaps.

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