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.