Review Note

• A free flap is where a tissue is lifted from a donor site and moved to a recipient site with an intact blood supply, compared to a graft, which doesn’t have an intact blood supply and relies on the growth of new blood vessels.
• Involves separation of the flap from the original vascular supply and microvascular reanastomosis at a distant site – associated with substantial transient ischemia of the tissue.
• Done to fill a defect from surgery/injury or to rebuild complex anatomic structures (e.g., breast or jaw).
• A free flap is the highest level of surgical complexity on the "reconstructive ladder" and has anaesthetic implications to maximize flap survival.
• Free flaps offer the best functional and cosmetic results but have a higher risk of failure due to:
  • Primary ischemia at the time of surgery.
  • Reperfusion injury and impaired post-op flow, leading to secondary ischemia.

Phases of Ischemia & Reperfusion

• Primary Ischemia:
  • Cessation of blood flow causes anoxia.
  • Anaerobic metabolism leads to lactate accumulation, pH drop, ATP depletion, calcium increase, and pro-inflammatory mediators.
  • Tissues with a high metabolic rate are more susceptible (muscle > skin).
  • Ischemia duration depends on surgical time (60-90 mins).
• Reperfusion:
  • Begins when vascular clamps are released.
  • Normally restores blood flow and reverses physiological derangement.
  • Prolonged ischemia or poor perfusion pressure increases the risk of reperfusion injury.
  • Reperfusion injury occurs when inflammatory substrates enter and destroy the flap.
• Secondary Ischemia:
  • Occurs post-transplantation if the flap suffers massive intravascular thrombosis and interstitial oedema.
  • Flaps tolerate 10-12 hours of ischemia, but irreversible changes occur at 4 hours.
• Failure Rates:
  • Most failures occur within the first 48 hours post-op due to venous thrombosis (more common than arterial occlusion).
  • Overall success rate = ~90%.
• Causes of Failure:
  • Arterial: Inadequate anastomosis, spasm, or thrombosis.
  • Venous: Defective anastomosis, spasm, or compression (poor positioning or tight dressings).
  • Oedema: Excessive crystalloid administration, trauma, or prolonged ischemia (flaps lack lymphatics, making them prone to oedema).
• Vascular Response:
  • Transplanted vessels lack sympathetic innervation but respond to local and humoral factors (e.g., circulating catecholamines).

Common Free Flap Types

• Latissimus Dorsi Flap – Muscle/musculocutaneous for large soft tissue defects.
• Scapular Flap – Fascial, fasciocutaneous, or osteocutaneous (mandible/maxilla reconstruction).
• TRAM Flap (Rectus Abdominis) – Muscle/musculocutaneous (used in glossectomy, orbit, skull base, breast reconstruction).
• Fibula Graft – Osseous/osteocutaneous (head & neck bony defects).
• DIEP Flap (Deep Inferior Epigastric Perforator) – Musculocutaneous (breast reconstruction).
• Radial Forearm Flap – Fascia+skin or bone+skin (head and neck reconstruction).
• Anterior Thigh Flap – Fascia+skin ± muscle.
• Gracilis Flap – Facial reanimation/sphincter reconstruction.
• Temporoparietalis Flap – Fascia+skin (head and neck defects).
• Omental Flap – Vascularized fat.
• Jejunal Flap – Pharyngeal and oesophageal reconstruction (low ischemic tolerance).

Factors Influencing Perfusion

• Blood flow through microcirculation depends on Starling forces (hydrostatic vs. oncotic pressure).
• Flow follows Hagen-Poiseuille equation:
• 
  

• • To maintain flow, optimize MAP, viscosity, and avoid vasoconstriction.
• Regulation of Microcirculation:
  • Neural: SNS control of vascular tone.
  • Humoral: Catecholamines.
  • Local Factors:
    • Metabolic: Increased K+, H+, osmolarity, adenosine, CO₂ → vasodilation.
    • Myogenic autoregulation: Constriction with high pressure, dilation with low pressure.
• Effects of Surgery on Blood Flow:
  • GA increases platelet aggregation, RBC rigidity, clotting factors, and plasma fibrinogen, while impairing fibrinolysis.
  • Transfused blood is less deformable (low 2,3-DPG).

Perioperative Management

Pre-Op Considerations

• Patient Assessment:
  • CVS status – Can the patient tolerate high CO for prolonged periods?
  • Flap failure risk factors – Smoking, diabetes, PVD.
• Surgical Planning:
  • Assess donor/recipient site (e.g., previous radiotherapy = poor vessel quality).
  • Vascular Imaging (CTA) – Ensures donor limb isn’t left ischemic.
• Anaesthetic Factors:
  • Airway assessment, regional anaesthesia options, fluid management plan.
  • Need for arterial line, CVL, HDU/ICU post-op care.

Intraoperative Management

• Optimizing Perfusion:
  • Maintain MAP, normothermia, and normocarbia.
  • Prevent vasoconstriction (adequate pain relief, fluid loading, avoiding vasopressors).
• Anaesthesia Techniques:
  • Propofol TIVA – Lowers SVR, antiemetic, inhibits platelet aggregation.
  • Remifentanil – Blunts SNS response.
  • Regional Anaesthesia – Enhances flap flow via vasodilation.
• Fluids:
  • Excess crystalloid = oedema = venous thrombosis = flap failure.
  • Restrict crystalloids to pre-op deficits & intra-op losses.
  • Goal = modest hypervolemia:
    • 10-20mL/kg pre-op losses + 4-8mL/kg/hr intra-op insensible losses.
    • >6mL/kg/hr fluids = ↑ flap failure risk.
  • Colloids may be used for haemodilution (target Hct 30-35%).
• Vasopressors:
  • No evidence of flap failure with low-dose vasopressors.
  • Consider beta-agonists (ephedrine, dobutamine) over pure alpha-agonists.
• Avoid Transfusions Unless Necessary – Transfused RBCs are less deformable.
• Anticoagulation:
  • Prophylactic LMWH recommended to reduce graft failure.

Post-Op Care

• Smooth Emergence – Avoid coughing/straining (prevents tension on suture lines).
• ICU/HDU monitoring – First 48 hours are critical.
• Flap Observations:
  • Pale, pulseless flap = arterial issue.
  • Swollen, dusky flap = venous congestion.
• Pain Management:
  • Regional/Epidural ideal, PCA, paracetamol.
  • Avoid NSAIDs for first 48 hrs (risk of bleeding).
• Early LMWH Introduction – Reduces thrombosis risk.
• Low threshold for surgical re-exploration if compromise suspected.