Anaesthesia for reconstructive surgery

Skin or tissue defects that cannot be closed primarily with simple suturing may need skin grafts, tissue expanders or flaps to maintain skin integrity and prevent infection. Flaps may be local, pedicled or free and may involve skin, muscle, bone, bowel or a combination. Local and pedicled flaps keep their primary vascular supply while free flaps have their circulation detached and reanastomosed distantly. Free flaps are therefore particularly vulnerable to ischaemia. Primary ischaemia occurs during the clamping of the vascular supply until anastomosis is completed and reperfusion achieved. Secondary ischaemia refers to any subsequent hypoperfusion and can be prevented by good anaesthetic technique and active fluid therapy. The guiding principle of anaesthesia for free flap surgery is the maintenance of optimum blood flow as summarized by the Hagen-Poiseuille equation. Thus, the goals of anaesthesia for free flap surgery are vasodilatation, good perfusion pressure and low viscosity. Balanced general anaesthesia, good analgesia and normothermia provide vasodilatation. Optimal perfusion pressure and low blood viscosity is achieved by modest hypervolaemic haemodilution guided by the CVP and haematocrit. In addition to basic monitoring, these patients require invasive blood pressure monitoring, CVP, temperature and urine output measurement. Active warming is started before induction of anaesthesia and continued into the post-operative period. A regional anaesthetic technique is preferred to cover the free flap recipient site. Careful positioning of the patient and prophylaxis against deep venous thrombosis is imperative for such a long operation.