Discussion:
Thumb replantation is an intricate procedure that necessitates venous anastomosis to prevent venous congestion in the attached appendage and eventual replantation failure (4). A meta-analysis published in 2018 evaluated the correlation between venous anastomosis and replant survival, they found that the higher the anastomosis number the higher the chance of survival. Zero versus one versus two anastomosis were evaluated, with two anastomosis showing a survival rate of 92.3% and 61.1% survival in zero anastomosis (5).
Venous anastomosis can be achieved by either hand-sewn technique or the use of couplers. A meta-analysis published in 2020 looked at studies comparing coupler use versus hand-sewn technique in venous anastomosis; it reported anastomotic time and postoperative complications. Their results showed that the use of couplers when compared to hand-sewn venous anastomosis significantly decreased anastomotic time and postoperative failure risk, but it did not decrease postoperative venous thrombosis risk (2). In one study, time reduction from approximately 12 minutes with hand-sewn anastomosis to 3 minutes with a coupler was noted (6).
One of the problems faced during the anastomosis phase of the replantation surgery is the post-traumatic vasospasm experienced by vessels in the zone of injury. Additionally, intra-operative vessels dissection and manipulation are also reasons for the narrowing of vessels. Vasospasm during microsurgery affects up 5-10% of the procedures due to the aforementioned reasons. There are several ways to deal with this issue; some of which are: mechanical dilation, perivascular lidocaine injection, axillary block anesthesia, and systemic papaverine use (3).
Papaverine was initially discovered in 1848 by Georg Merk (7). It is a phosphodiesterase (PDE) inhibitor commonly used in microsurgery. It antagonizes the PDE that breaks down cyclic guanosine monophosphate (cGMP) thus increasing the concentration of this second messenger within the vessel’s smooth muscles, consequently inhibiting the effect of myosin light chain kinase and thus causing vasodilation (8). It is approved for the use in cerebral vasospasm, biliary duct spasms, and erectile dysfunction through its anti-spasmodic action on smooth muscles (9,10,11). One study looked at the time of action of papaverine in preventing vasoconstriction in response to phenylephrine and potassium (60 mmol/L); it showed that it reversed vasoconstriction for a maximum of only one hour (12). Another study looked at the effect of preventing vasoconstriction on the radial artery during coronary artery bypass grafting (CABG) in vitro. The radial artery was pre-treated with papaverine and prevention of vasoconstriction to norepinephrine was tested; results showed that the effect of papaverine was lost after eight hours (13).
An article published in 2016 looked at the alternative drugs that can be given in the case of shortage of papaverine. Topical lidocaine and nicardipine (calcium channel blocker) were used as alternative antispasmodics and the rates of re-exploration, complications, and flap salvage were compared when matched with papaverine controls. Results showed that there was no higher risk of flap loss or re-operation, making these drugs safe and effective alternatives to papaverine (7). Other anti-spasmodic were studied in animal models; for example, phosphodiesterase inhibitors (pentoxifylline, papaverine, and amrinone), calcium channel blockers (verapamil, nicardipine, nifedipine, and magnesium sulfate), local anesthetics (lidocaine), alpha antagonists (chlorpromazine and phentolamine), and direct vasodilators (prostaglandin E1, sodium nitroprusside, hydralazine, and nitroglycerin). However, to guide evidence-based management, well-controlled translational studies are required in order to reliably generalize the data (14).
In our case, there was no salvageable vein for anastomosis except one superficial vein with a diameter of 0.7mm and the smallest coupler size was 1mm, so we gave the patient a trial of topical papaverine, 1mg/ml, to vasodilate the vein. Several cycles were given in addition to mechanical dilation and finally the vein could accommodate the 1mm coupler and anastomosis of the veins was possible in 25 minutes; 30% increment in the vein diameter was achieved. The coupler was covered with a small skin flap. Consequently, the thumb survived with no post-operative complications.