A prospective study of transit-time flow volume measurement for intraoperative evaluation and optimization of free flaps

BACKGROUND: Transit-time flow volume measurement, a non-Doppler-based ultrasound technology, has been shown to accurately evaluate the quality of coronary artery bypass grafts and improve outcomes of cardiac surgery. The authors hypothesized that it would also improve decision making in microvascular free tissue transfer procedures. METHODS: The authors measured transit-time flow volume in 52 consecutive free flaps at three times: measurement 1 (in situ), after flap elevation and isolation on its pedicle; measurement 2 (time 1), immediately after anastomosis and reperfusion; and measurement 3 (time 2), 30 minutes after anastomosis and reperfusion. Intraoperative decisions based on transit-time flow volume were documented. RESULTS: Arterial inflow was on average 1.5 times greater than venous outflow, and arterial resistance was 3.59 times greater than venous resistance. Free transverse rectus abdominis musculocutaneous flaps had the highest venous and arterial flows, and free radial forearm flaps had the lowest. Compared with the baseline (in situ) measurement, all flaps had higher flows immediately after transfer (time 1) (p < 0.0001), but no significant differences were seen 30 minutes later (time 2) (p = 0.68). Arterial resistance, however, increased during that interval (p = 0.006). Operative decisions, including selection of the higher flow vena comitans (sometimes the smaller of the two) and when to revise an anastomosis, were modified on the basis of volume findings in 19 of 52 cases (36.5 percent). CONCLUSIONS: Transit-time flow volume provides novel physiologic flap data and identifies flawed anastomoses and higher flow venae comitantes. These data have clinical value in microsurgery and might reduce microvascular complications and improve outcomes. CLINICAL QUESTION/LEVEL OF EVIDENCDE: Diagnostic, IV.