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.