Discussion and Conclusions
Reconstruction of a resected tissue with a free flap involves the
transfer of a tissue comprehensive of its vascular peduncle from a donor
to a recipient site. In order to ensure adequate blood supply of the
free flap and its engraftment in the new body area, reconstruction of
the vascular tree performing microvascular anastomosis is necessary.
This is especially important in the pediatric population to ensure
adequate growth of the graft together with the rest of the body during
puberty.
Late engraftment or ischemia with possible successive necrosis of the
flap can happen in the postoperative period if constant sufficient blood
supply is not provided. Tissue hypoperfusion related to low blood
pressure and thrombosis of the new anastomosis are among the most common
causes of flap dysfunction.
Concerning hypoperfusion there are different strategies that can be
employed, mostly strict monitoring of blood pressure with target
normotensive values in the last phases of the surgery (after reperfusion
of the graft) and in the first postoperative days, and maintenance of a
NIRS probe over the skin area near the vascular anastomosis to detect
possible progressive decrease in the NIRS values as sign of increased
extraction of oxygen by peripheral tissues and if protracted
hypoperfusion.
Thrombosis can occur at the level of venous or arterial anastomosis.
Platelet aggregation is the underlying cause of arterial thrombosis
whereas venous thrombosis is primarily the result of fibrin clotting and
has three main predisposing factors for its development (Virchow’s
triad): hypercoagulability, stasis and endothelial damage which
predisposes to turbulent flow.
There are no evidence-based guidelines for the prevention of
microvascular thrombosis after free tissue transfer in head and neck
surgery. In practice, most surgical patients receive intravenous heparin
50 UI/kg in the operating room immediately before the reperfusion of the
graft and then, in the postoperative days, prophylaxis of deep vein
thrombosis with subcutaneous heparin, often associated with aspirin,
milrinone and dextran. The high dosage of heparin administered during
the surgery carries a high risk of complications, above all formation of
hematomas, thrombocytopenia and bleeding. (3)
In this paper we show that lower UI/kg of unfractionated heparin can be
enough to obtain adequate anticoagulation in children and ACT can be a
valid method to monitor the response to the initial bolus and, when
repeated at regular intervals during the surgery, eventual need of
additional heparin. A substantial reduction of the risk of thrombosis is
possible avoiding main systemic side effects. The second aspect of this
paper is the importance of pain control following free flap microsurgery
allowing early mobilization which can be reached with different
techniques: parenteral opioids, epidural analgesia and peripheral nerve
blocks. The ongoing goal in the fields of anesthesia and surgery is to
provide a combination of reliable analgesia while minimizing adverse
side effects. In this direction the loco-regional anesthesia is the best
option; peripheral nerve blocks carry in fact less side effects compared
to epidural anesthesia (epidural hematomas, urinary retention, spinal
headache, hypotension, motor weakness, and hemodynamic instability from
the sympathectomy) while providing satisfactory pain management both at
rest and during mobilization making it well tolerated by the patient.
(3,4) In this case, we have seen as a sciatic nerve catheter with
continuous infusion of ropivacaine provided effective analgesia for
postoperative in patient undergoing free flap microsurgery and how the
reduction in pain and side effects allowed for early ambulation,
improving postoperative rehabilitation and patient satisfaction, while
decreasing length of hospital stay and risk for nosocomial infections.
Current practices remain extremely diverse and the present report
represents an example of avoiding anastomosis thrombosis with very low
doses of intravenous heparin and a fast recovery due to perineural
continuous block. Further prospective studies could improve the quality
of available evidence.