The intrinsic transit time of free microvascular flaps: clinical and prognostic implications

Microscope-integrated indocyanine green near-infrared videoangiography (ICGA) is a new method for the intraoperative assessment of vascular flow through microvascular anastomoses. The intrinsic transit time (ITT) describes the time period from the dye appears at the arterial anastomosis (t(1)) till it reaches the suture line of the venous anastomosis (t(2)). As the transit time reflects blood flow velocity within the flap, prolonged ITT might correlate with low blood flow and a higher rate of postoperative thrombosis. We performed a clinical trial evaluating the association between intraoperative free flap transit time and early anastomotic complications in elective microsurgery.

One hundred consecutive patients undergoing elective microsurgical procedures underwent intraoperative ICG angiography (ICGA). In patients with anastomotic patency, angiograms were retrospectively reviewed and the intrinsic transit time was calculated. Postoperative outcome was registered and compared with the ITT. End points included early reexploration surgery and flap loss within the first 24 hours after surgery.

Fourteen patients were excluded from the study due to technical anastomotic failure. The overall flap failure rate was 6% (5/86); the incidence of early re-exploration surgery was 10% (9/86). With a median of 31 seconds patients with an uneventful postoperative course showed significantly shorter ITTs than patients with flap loss or early postoperative reexploration (median: >120 seconds). An optimal cut-off value of ITT > 50 seconds was determined to be strongestly associated with a significantly increased risk of at least one positive end point.

This study demonstrates a significant predictive value of the intrinsic flap transit time for the development of flap compromise and early re-exploration surgery.