Letter to the Editor: Response to Manzano Surroca et al. "Poland Sequence: Retrospective Analysis of 66 Cases." Annals of Plastic Surgery, May 2019.

Sir: M omeni et al conclude that breast reconstruction using abdominal free flaps can cause venous stasis, increasing the risk of deep venous thrombosis (DVT). Surprisingly, the authors do not report their actual data but rather percent changes of the (presumably) means, represented on a single illustration with an unlabeled horizontal axis. The average length of hospitalization, and therefore timing of the last scan, is not provided. There was no control group. The error bars are remarkably tight and uniform, with wide spacing that suggests highly significant and consistent changes. Substantial variability is known to affect repeated ultrasound measurements of the common femoral vein diameter and blood velocity. All patients received chemoprophylaxis, differing from recent recommendations. One patient developed a pulmonary embolism (3.3%) 10 days postoperatively, evidently from an undetected DVT. The authors report a 19.1% dilation of the left common femoral vein and a 10.9% reduction in maximal flow velocity on the day after surgery. These changes were almost identical on the date of discharge from hospital. It is difficult to reconcile the percent change in the lumen diameter with the percent change in velocity. For a constant flow rate (in cubic centimeters per second), the blood velocity should decrease inversely proportionally with the square of the vessel diameter (1/r). A 19.1% increase in diameter should produce a 29.5% reduction in velocity. However, the authors report a reduction in velocity of only 10.9%. If the data are correct, the blood volume flowing into and out of the lower extremity must increase 26% and remain elevated on the date of discharge, requiring a 26% increase in cardiac output. This change could be achieved by sustained tachycardia, yet (fortunately) none is reported. The authors believe that repair of the abdominal muscle fascia impedes venous return