A 52-year-old man undergoes elective abdominal wall reconstruction after a large ventral hernia repair. On postoperative day 14, the wound shows good epithelialization and early scar formation. All of the following factors are known to impair wound healing at this stage EXCEPT:

Question

Accepted Answer

A. Increased wound oxygen tension and high FiO₂ supplementation promoting fibroblast activity. ## Factors Impairing Wound Healing in the Proliferative Phase

**Key Point:** The proliferative phase (days 3–21) depends on adequate oxygen, nutrients, and growth factor signaling. Most systemic and local factors that impair healing reduce these resources; increased oxygen tension and FiO₂ actually **enhance** healing and do not impair it.

### Systemic Factors Affecting Wound Healing

| Factor | Effect on Healing | Mechanism |
|--------|-------------------|----------|
| Corticosteroids | ↓ Impairs | Suppresses fibroblast proliferation, inhibits collagen cross-linking, reduces angiogenesis |
| Hyperglycemia (>180 mg/dL) | ↓ Impairs | Impairs neutrophil chemotaxis, reduces angiogenesis, increases infection risk |
| **High oxygen tension / FiO₂** | **↑ Enhances** | **Promotes fibroblast activity, collagen synthesis, angiogenesis** |
| Protein malnutrition | ↓ Impairs | Reduces amino acid substrate for collagen (proline, lysine, glycine) |
| Vitamin C deficiency | ↓ Impairs | Blocks hydroxylation of proline and lysine; collagen becomes unstable |
| Anemia (Hb <7 g/dL) | ↓ Impairs | Reduces oxygen delivery to wound |
| Infection | ↓ Impairs | Consumes nutrients, triggers excessive inflammation |

### Why Option 3 Is Correct (Does NOT Impair Healing)

**High-Yield:** Increased wound oxygen tension and supplemental FiO₂ are **beneficial**, not harmful, to wound healing. Oxygen is essential for:
  1. Hydroxylation of proline and lysine in collagen (requires O₂ as a cofactor for prolyl and lysyl hydroxylases)
  2. ATP production for fibroblast and endothelial cell function
  3. Bacterial killing by neutrophils (oxidative burst)
  4. Angiogenesis and neovascularization

**Clinical Pearl:** Supplemental oxygen (FiO₂ 40–50%) is recommended perioperatively to reduce surgical site infection and promote healing, particularly in high-risk patients (diabetics, elderly, obese).

### Why the Other Options Impair Healing

- **Option 1 (Corticosteroids):** Suppress fibroblast proliferation, inhibit collagen cross-linking, and reduce angiogenesis — well-documented mechanism of impaired healing.
- **Option 2 (Hyperglycemia):** Impairs neutrophil chemotaxis and function, reduces angiogenesis, and increases infection risk — major risk factor in diabetic wound healing.
- **Option 4 (Protein malnutrition):** Collagen is ~30% glycine, ~10% proline, ~1% lysine. Deficiency of these amino acids directly reduces collagen synthesis and tensile strength.

**Mnemonic — CHIMPANZEES (Factors Impairing Wound Healing):**
- **C**orticosteroids
- **H**yperglycemia
- **I**nfection
- **M**alnutrition (protein, vitamin C, zinc)
- **P**oor perfusion / anemia
- **A**ge (elderly)
- **N**ecrotic tissue
- **Z**inc deficiency
- **E**xcessive tension
- **E**dema
- **S**moking

Answer

B. Chronic corticosteroid use suppressing fibroblast proliferation and collagen cross-linking

Answer

C. Severe protein malnutrition reducing amino acid availability for collagen synthesis

Answer

D. Elevated serum glucose (>180 mg/dL) impairing neutrophil chemotaxis and angiogenesis

A 52-year-old man undergoes elective abdominal wall reconstruction after a large ventral hernia repair. On postoperative day 14, the wound shows good epithelialization and early scar formation. All of the following factors are known to impair wound healing at this stage EXCEPT:

Explanation

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