Effect of ischemia and reperfusion on neutrophil accumulation in equine microvascular tissue flaps.

Objective: To investigate neutrophil accumulation after ischemia and reperfusion (IR) in microvascular tissue flaps in horses.

Study Design: Randomized controlled experiment.

Sample Population: A total of 8 horses between 1 and 10 years of age, 4 of each sex.

Methods: Control and experimental myocutaneous island flaps based on the superficial branch of the deep circumflex iliac vessels were dissected on each horse. Atraumatic vascular clamps were applied to the pedicle of the experimental flap for 90 minutes and then removed to allow reperfusion. Based on the assumption that rapid infiltration of neutrophils into affected tissues is a hallmark of IR injury, radiolabeled autogenous leukocytes were used to indirectly quantify neutrophil accumulation in flap tissues. Labeled leukocytes were administered through a jugular catheter 30 minutes before flap reperfusion. Biopsies were collected from each flap over a 6 hour postischemia time period; in group 1 (n = 4) from 0 to 6 hours postischemia, and in group 2 (n = 4) from 24 to 30 hours postischemia. Biopsies were examined scintigraphically and histologically for evidence of neutrophil infiltration.

Results: All control flaps survived and 6 of 8 experimental flaps survived. There was no significant evidence of acute neutrophil infiltration into flap tissues after reperfusion in either group.

Conclusions: The results of this study suggest that equine myocutaneous flap tissues can survive a 90-minute ischemic period and reperfusion. No significant evidence of the occurrence of IR injury in flap tissues was found.

Clinical Relevance: The reasons for the previously reported failures of equine free tissue transfer remain uncertain, but they do not appear to be caused by neutrophil mediated injury associated with ischemia and reperfusion.