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Aneurysm formation has been a major complication in laser-assisted micro vascular anastomosis (LAMA). The authors investigated the effect of increased laser energy on the formation and growth rate of aneurysms. In addition, possi ble methods of prevention were reviewed. End-to-end anastomoses were per formed on 89 rat femoral arteries with the placement of three stay sutures (120 degrees apart) followed by application of CO2 laser irradiation (power = 80 mW, pulse mode = 0.2 s, spot size = 0.275 m). In Group I (N=55), anasto moses were performed with 45 laser pulses, and in Group II (N = 34) 135 laser pulses were used. Each disruption of an anastomosis was repaired by use of 15 additional laser pulses. Six of 18 aneurysms in Group I were reevaluated at weeks 1, 3, and 8 to assess growth rate. All vessels were examined at week 3 for patency and aneurysm formation. Overall aneurysm rates in the two groups were similar, despite the increased laser energy used in Group II (p > 0.05). There was a higher incidence of aneu rysm formation in disrupted vessels in both groups when compared with non- disrupted vessels (p < 0.05 in Groups I and II). The aneurysm rates did not differ between the two groups when vessels with no disruption or with 1 disrup tion were compared (p > 0.05). Mean aneurysm size increased 0.4 mm/week during the first week, 0.25 mm/week during the second and third weeks, and less than 0.1 mm/week during the remaining five weeks. In conclusion, the authors have shown that aneurysm formation is not re lated to the total amount of laser energy applied and that disrupted anastomoses have higher aneurysm rates independent of laser energy. Aneurysm growth rate is maximal during the first week.

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