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Gangrene - Bailey & Love's Short Practice of Surgery (28th Ed.)

Final Year MBBS Examination Notes - 25 Marks Each

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DEFINITION

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1. DRY GANGRENE (25 Marks)

Definition

Aetiology

• Gradual progressive arterial occlusion - commonest cause is atherosclerosis
• Other causes: Buerger's disease (thromboangiitis obliterans), Raynaud's disease, severe frostbite, ergotism
• The key feature is that occlusion is gradual, allowing collateral circulation to partially develop, preventing superadded infection

Pathology

• Gradual arterial obstruction leads to progressive ischaemia
• Venous return is also impaired; fluid cannot enter the dead tissue
• Tissue dries out, shrivels and becomes mummified
• Haemoglobin breaks down to iron sulphide - produces the black discolouration
• The part becomes hard, dry, shrunken, and wrinkled (like a mummy)
• Putrefaction is absent or minimal as the dry, avascular tissue resists bacterial growth

Clinical Features

Line of Demarcation

• A zone of demarcation between truly viable and dead tissue will eventually appear
• Separation is achieved by the development of granulation tissue between dead and living parts
• In dry gangrene, if blood supply of proximal tissues is adequate, the final line of demarcation appears in a matter of days and separation occurs neatly and with minimum of infection
• If bone is involved, complete separation takes longer; the stump tends to be conical as bone has a better blood supply than its coverings

Management

1. Conservative - Allow dry gangrene to demarcate spontaneously; no soaking or ointments needed
2. Treat underlying cause - Arteriography and revascularisation (bypass surgery or angioplasty) to improve proximal circulation
3. Surgical debridement - After demarcation, conservative amputation at the lowest viable level
4. Major limb amputation - Required when: blood supply cannot be improved, life-threatening sepsis develops, limb non-functional

Key Principle

Amputation in the presence of poor circulation will fail - gangrene will reappear in wound edges. The arterial supply must be assessed and improved first.

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2. WET GANGRENE (25 Marks)

Definition

Aetiology

• Sudden arterial occlusion (e.g., embolism) with no time for collateral circulation to develop
• The venous drainage continues briefly, allowing oedema and bacterial invasion
• Predisposing factors: diabetes mellitus, immunocompromised state, venous outflow obstruction

Pathology

• Sudden arterial blockage leads to rapid tissue necrosis
• The affected part is oedematous (venous return initially maintained)
• Putrefactive bacteria (saprophytes) invade the necrotic tissue
• Putrefaction releases gases - hence crepitus may be present
• Tissue liquefaction occurs
• Haemoglobin breakdown produces the black/green discolouration
• Toxins released by bacteria are absorbed systemically - patient becomes severely ill/septic

Clinical Features

Line of Demarcation

• In moist gangrene, the infection and suppuration extend into the neighbouring living tissue, causing the final line of demarcation to be more proximal than in dry gangrene
• If arterial supply to proximal living tissue is poor, the line of demarcation is very slow to form or may not develop at all
• Gangrene may spread to adjacent tissues or appear as 'skip' areas further up the limb on the other side of the foot, the heel, dorsum, or even the calf

Differences from Dry Gangrene

Management

1. Emergency surgery - Urgent debridement or amputation - this is a surgical emergency
2. IV antibiotics - Broad-spectrum covering aerobic and anaerobic organisms
3. Resuscitation - IV fluids, correction of septic shock
4. Control underlying disease - Especially diabetes mellitus
5. Revascularisation - Where possible, to improve limb salvage
6. Amputation level - Higher than in dry gangrene due to proximal spread of infection

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3. GAS GANGRENE (25 Marks)

Definition

Causative Organism

• Clostridium perfringens - Gram-positive, anaerobic, spore-bearing bacilli
• Widely found in nature, particularly in soil and faeces
• Spores survive in soil for years

Predisposing Factors / At-Risk Patients

• Immunocompromised patients
• Diabetic patients
• Patients with malignant disease
• Wounds containing necrotic or foreign material (anaerobic conditions)
• Military wounds - high-velocity missiles or shrapnel cause extensive tissue damage; the cavitation following passage of a missile creates a 'sucking' entry wound, leaving clothing and environmental soiling in addition to devascularised tissue
• Amputations performed for peripheral vascular disease with open necrotic ulceration

Pathogenesis

• Contaminated wound provides anaerobic environment ideal for Clostridium to germinate from spores
• Organism releases powerful exotoxins:
  • Alpha toxin (lecithinase/phospholipase C) - most important; causes haemolysis, myonecrosis, platelet destruction
  • Collagenase - breaks down connective tissue
  • Hyaluronidase - facilitates spread through tissue planes
  • Other proteases
• Gas (mainly CO₂ and H₂) produced by bacterial metabolism accumulates in tissues
• Rapid local spread → circulatory collapse → multi-organ failure

Clinical Features

Local Features

Systemic Features (Rapid Onset)

• High fever, tachycardia, hypotension
• Haemolysis and haemolytic anaemia
• Circulatory collapse
• Organ failure (renal, hepatic)
• Death if not treated promptly

Investigations

1. Plain X-ray - Gas in the soft tissues (pathognomonic)
2. CT scan - Extent of gas and tissue involvement
3. Wound swab - Gram stain (Gram-positive bacilli, no pus cells)
4. Blood cultures
5. FBC - Haemolytic anaemia, leucocytosis
6. Renal and hepatic function tests

Treatment (Summary box 5.9 / Summary box 33.9)

1. Surgical (Most Important)

• Radical and regular surgical excision of all affected tissue is the cornerstone of treatment
• Wound should be widely opened and all necrotic muscle excised
• Re-examine wound at 24-48 hours and repeat debridement as needed ("radical and regular" surgical excision)
• Early amputation may be life-saving - do not delay when limb is extensively involved
• Fasciotomy to decompress compartments

2. Antibiotic Therapy

• Large doses of IV penicillin (Penicillin G) - drug of choice
• Metronidazole - additional anaerobic cover
• Antibiotic prophylaxis should always be considered in patients at risk, especially when amputations are performed for peripheral vascular disease with open necrotic ulceration

3. Supportive

• High-dose oxygen (the organism is anaerobic; high-oxygen environment is bacteriostatic)
• Hyperbaric oxygen (HBO) - where available; inhibits toxin production and bacterial growth
• Aggressive IV fluid resuscitation
• Correction of haemolytic anaemia
• Intensive care management for organ support
• Antitoxin (where available)

Summary Box (Bailey & Love)

• Caused by C. perfringens
• Spores are present in soil
• Thrives in anaerobic conditions and produces many exotoxins
• Treat with radical and regular surgical excision
• Give oxygen and penicillin
• Early amputation may be life-saving

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QUICK COMPARISON TABLE - All Three Types

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IMPORTANT POINTS FOR 25-MARK ANSWER STRUCTURE

1. Definition (2 marks)
2. Aetiology / Causes (3 marks)
3. Pathology (5 marks)
4. Clinical Features (5 marks)
5. Investigations (3 marks)
6. Treatment / Management (5 marks)
7. Complications (2 marks)