Normal phases of wound healing:
Haemostasis
- Platelet aggregation, activation of clotting cascade and formation of fibrin clot
- Platelets release serotonin, cytokines, growth factors, thromboxane
- Vasoconstriction at site of injury, with surrounding vasodilation mediated by histamine to get important healing factors to area
Inflammation
- Lasts about 5 days
- Fibrin clot acts as scaffold for inflammatory cells (neutrophils, leukocytes, macrophages)
- Macrophages are principal healing cells – arriving around day 3 – antimicrobial effects, phagocytosis of debris, angiogenesis, regulation of matrix synthesis, further cell recruitment and activation
- Towards end of inflammatory phase, fibroblasts and lymphocytes arrive
Proliferation
- About day 3 to 14 – increase in fibroblasts and loss of neutrophils
- Fibroblasts and macrophages further form extracellular matrix synthesis and begin collagen synthesis – replacing the initial fibrin scaffold
- Epithelial cells proliferate at wound edges and granulation tissue fills defects, angiogenesis
Maturation
- About day 8 to 3 months
- Macrophages and neutrophils leave
- Cardinal feature is deposition of collagen with increasing tensile strength over time
Final part of healing is wound contraction – mediated by myofibroblasts – with final approximation of wound edges and shortening of scar
Healing by secondary intention:
- Epithelialisation occurs from basal cells of epidermis at margins of wound, with mitosis of basal cells occurring until defect is covered
- Contraction plays far more important role
Complications of healing:
- Infection
- Wound dehiscence
- Excessive granulation
- Keloid scar
- Pigmentation
- Pain
- Cicatrisation
- Implantation cyst
- Neoplasia
Factors affecting wound healing:
Local factors:
- Poor blood supply (ischaemia)
- Adhesion to underlying structures
- Direction of wound
- Tension
- Dead space
- Haematoma
- Infection
- Foreign body
- Movement
- Drying
- Neoplasia
- Radiation
General factors:
- Age
- Nutrition
- Hormones
- Temperature
- Immunosuppression
- Obesity
- Hypovolaemia
- Smoking
Surgical site infections – diagnosed within 30 days of procedure (exception for implants – within one year)
- Superficial SSI – above fascia
- Deep SSI – fascia and muscle
- Organ space SSI – e.g., peritonitis
Dehiscence – mechanical failure of wound healing and separation of fascial layers early in postoperative period
Manifests as sudden dramatic drainage of large volume of clear serous fluid from incision, sometimes with pulling or ripping sensation
Probe with sterile cotton tip probe or similar +/- imaging will give diagnosis
Evisceration – extrusion of peritoneal contents through dehisced wound
Cover with sterile saline soaked packs until theatre
Risk factors for dehiscence:
- Obesity
- Immunosuppression / steroids
- Smoking
- Radiation
- Cancer
- Malnutrition
- Diabetes
Fascial strength:
- 50 – 60 % at 6 weeks
- 70 – 90 % at 20 weeks
Dehiscence may occur due to:
- Suture may break
- Knot may slip
- Suture may tear through tissue – most common – hence use of larger suture like 0-PDS
Aim for > 1 cm from fascial edge, advancing no more than 1 cm each throw.
Effect of radiation on healing
Radiation therapy works by induced double strand breaks in DNA.
Can be direct damage (direct ionisation effects on DNA) or more predominantly indirect damage (production of free radicals which damage DNA). SBRT may also cause direct cell apoptosis and cell membrane disruption with higher doses per fraction.
Radiation causes significant alterations in several cell signalling molecules – interferons, VEGF, NO, TNF and interleukins.
Downstream effects of all of these causes disorganisation in the extracellular matrix, impairment of neovascularisation and reduction in cell migration, and disordered collagen deposition
Findings in radiated tissue include:
- Disruption or absence of normal tissue planes
- Abundance of scar tissue
- Tissue atrophy
- Loss of tensile strength can cause tearing during usual blunt dissection manoeuvres
Principles for operating on radiated fields:
- Even if tissue looks normal, it is likely that vascularity, pliability and healing are compromised
- Higher likelihoods of leaks, strictures, need for reoperation
- Minimise mobilisation
- Interposition of healthy tissues
- Diversion if needed
- Ensure normal principles for healing – avoiding infection, optimising nutrition
Hyperbaric oxygen:
- Stimulation of angiogenesis
- Reduction of fibrosis
- Improved tissue oxygenation
- Stimulation of stem cells and derivatives
- May be useful adjunct for operations on radiated patients
- 100 % FiO2 at 2 atm
- Ideally 40 sessions, 2 hours per session
- Side effects – visual changes, ear pressure changes
- Contraindications – untreated pneumothorax is absolute contraindications, relative include active chemo treatment (doxorubicin, bleomycin, platinum), COPD, pregnancy, inability to equalise, claustrophobia