What is the critical pressure threshold at which compartment syndrome becomes inevitable and tissue necrosis begins, relative to diastolic blood pressure?

Explanation

## Critical Pressure Threshold in Compartment Syndrome **Key Point:** The widely accepted fasciotomy threshold — and the point at which irreversible ischemic injury becomes imminent — is when intracompartmental pressure rises to within **30 mmHg of the diastolic blood pressure** (i.e., Δp ≤ 30 mmHg). This is the standard taught in Rockwood & Green's *Fractures in Adults* and endorsed by the American Academy of Orthopaedic Surgeons. ### Pathophysiological Basis When compartment pressure approaches diastolic BP, the arteriovenous pressure gradient across the capillary bed falls below the critical closing pressure (~30 mmHg). At this point, microvascular perfusion ceases and the tissue oxygen debt accelerates toward irreversible necrosis. Fasciotomy performed **at** this threshold prevents necrosis; delay beyond it allows necrosis to begin. ### Pressure Decision Framework | Δp (Diastolic BP − Compartment Pressure) | Clinical Action | |---|---| | > 30 mmHg | Monitor closely; serial pressure measurements | | **≤ 30 mmHg** | **Fasciotomy indicated — imminent ischemia** | | 0 mmHg (equal to diastolic) | Complete capillary collapse; necrosis underway | **Clinical Pearl:** For a patient with diastolic BP of 70 mmHg, fasciotomy is indicated when compartment pressure reaches **≥ 40 mmHg** (i.e., 70 − 30 = 40 mmHg). Waiting until pressure equals diastolic BP (70 mmHg) guarantees irreversible damage. **High-Yield Mnemonic — "30-30 Rule":** Fasciotomy threshold = Diastolic BP − **30** mmHg. The 30 mmHg delta is the last safe window before tissue necrosis becomes unavoidable. > *Reference: McQueen MM, Court-Brown CM. Compartment monitoring in tibial fractures. J Bone Joint Surg Br. 1996; Rockwood & Green's Fractures in Adults, 9th ed.*