Acute Compartment Syndrome

Acute compartment syndrome (ACS) is a surgical emergency in which raised pressure within a closed osteofascial compartment reduces tissue perfusion enough to cause muscle and nerve ischaemia and necrosis. It occurs most often in the leg (anterior and deep posterior compartments) and forearm, but also in the thigh, hand, foot, buttock and abdomen.

The commonest cause is fracture (tibial shaft fractures 1 to 10% and forearm fractures about 3%). Other causes are crush injuries, soft tissue contusion, vascular injury and reperfusion, tight casts or dressings, burns, intravenous infusion extravasation, snake bite, prolonged limb compression (after drug overdose or surgery in lithotomy position) and anticoagulant haematoma. Young men (under age 35) and children are at higher risk.

Irreversible muscle damage starts after 4 to 6 hours of ischaemia, and nerve damage after 2 to 4 hours of severe ischaemia. Complications are muscle necrosis, permanent nerve deficit, Volkmann ischaemic contracture, rhabdomyolysis with acute kidney injury and hyperkalaemia, infection after fasciotomy, amputation, and death.

Pathophysiology.

Bleeding and oedema in a closed compartment increase interstitial pressure. When pressure approaches diastolic pressure the capillary blood flow stops, though arterial pulses stay present because the pressure is lower than systolic pressure. Ischaemic muscle swells further, which sets up a vicious cycle. Hypotension lowers the threshold for ischaemia.

Perfusion pressure is the diastolic blood pressure minus the compartment pressure (delta pressure). A delta pressure of under 30 mmHg indicates a compartment syndrome.

Pain out of proportion to the injury, worsening with time, not relieved by analgesia, and made worse by passive stretching of the muscles in the compartment. This is the key early sign. Other findings are a tense, swollen, firm compartment, paraesthesia (an early nerve sign), and paresis.

Pulselessness and pallor occur late and their absence does not exclude the diagnosis. In children the "3 A's" (increasing analgesia requirement, anxiety and agitation) are the early signs. In unconscious or sedated patients, rely on pressure measurement and the clinical context. Regional anaesthesia and nerve blocks can mask pain.

• The diagnosis is clinical. Do not wait for investigations when the findings are clear.
• Intracompartmental pressure measurement (handheld monitor, an arterial line transducer or a Stryker device) when the diagnosis is uncertain or the patient is unconscious: an absolute pressure of over 30 mmHg, or a delta pressure of under 30 mmHg (diastolic pressure minus compartment pressure), supports fasciotomy.
• Creatine kinase, potassium, creatinine, urinary myoglobin, lactate and blood gases for rhabdomyolysis and acute kidney injury.
• Near infrared spectroscopy and ultrasound are adjuncts.

Differential diagnosis.

• Arterial injury or acute limb ischaemia.
• Deep vein thrombosis and cellulitis.
• Fracture pain and necrotising fasciitis.
• Nerve injury and rhabdomyolysis without compartment syndrome.

Immediate measures.

• Remove all circumferential dressings, casts, splints and bandages down to the skin. Split a cast and padding on both sides along the whole length. Place the limb at the level of the heart (not elevated, because elevation lowers arterial perfusion).
• Give high flow oxygen and maintain blood pressure. Treat hypotension and hypovolaemia.
• Stop epidural or regional anaesthesia infusions that may mask pain, and review the analgesic requirement hourly.
• Refer to orthopaedics, plastic or vascular surgery immediately.

Fasciotomy. Urgent open fasciotomy of all affected compartments within 6 hours of onset (earlier when possible), once the diagnosis is made.

• Leg: two incision four compartment fasciotomy (lateral incision for the anterior and lateral compartments, and a medial incision 2 cm behind the tibia for the superficial and deep posterior compartments). Make long incisions of 15 to 20 cm and release the fascia along its length.
• Forearm: volar incision (curved from the medial epicondyle across the carpal tunnel) with release of the lacertus fibrosus and carpal tunnel, and a dorsal incision for the dorsal compartment if still tense.
• Other sites: thigh, hand (dorsal interosseous), foot (dorsal and medial incisions), gluteal and abdominal decompression.
• Debride non-viable muscle at the first look. Leave wounds open, and cover them with negative pressure dressings. Second look at 24 to 48 hours, with delayed primary closure or split skin grafting at 3 to 7 days.
• Fix the fracture at the time of fasciotomy, using external fixation or intramedullary nailing.

Rhabdomyolysis prevention. Isotonic crystalloid (0.9% sodium chloride) intravenously, 1 to 2 L in the first hour, then 200 to 300 mL/h. Keep the urine output over 200 to 300 mL/h until creatine kinase is under 5000 units/L (monitor for fluid overload and electrolytes). Treat hyperkalaemia (calcium gluconate 10% 10 mL intravenously over 10 minutes, with insulin and glucose) and consider renal replacement therapy for refractory hyperkalaemia, acidosis or oliguria.

Operative antibiotic prophylaxis. Cefazolin 2 g intravenously (3 g when weight is 120 kg or over) within 60 minutes before incision as a single dose (repeat after 4 hours or blood loss over 1500 mL). With severe penicillin allergy, vancomycin 15 mg/kg intravenously starting 90 to 120 minutes before incision as a single dose, with levels and creatinine checked in prolonged cases.

Analgesia.

• Paracetamol 1 g intravenously or orally every 6 hours (maximum 4 g daily; 3 g daily when weight is under 50 kg, with chronic alcohol use or hepatic impairment).
• Morphine 2.5 to 5 mg intravenously every 5 to 10 minutes as needed, titrated to pain (halve the dose with age over 75, haemodynamic instability or eGFR under 30 mL/min/1.73 m2; reassess after 10 mg). Monitor respiratory rate, oxygen saturation and blood pressure continuously.
• Avoid NSAIDs because of acute kidney injury risk with rhabdomyolysis.

Monitoring. Limb perfusion, compartment tension, sensation and motor function hourly in the first 24 hours. Delta pressure continuously when measured. Creatine kinase, potassium and creatinine every 6 to 12 hours until stable. Urine output hourly. Wound review at each dressing change. Rehabilitation and splinting to prevent contracture.

Referral and escalation. Emergency: refer on suspicion to the senior surgeon; fasciotomy should be available within the hour. Escalate for hyperkalaemia, oliguria, myoglobinuria or sepsis. Involve plastic surgery for wound cover and nephrology for renal replacement.

Special groups.

• Children: pain assessment is unreliable; use the 3 A's, a low threshold for pressure measurement, and early fasciotomy.
• Unconscious and ventilated patients: measure pressure in every high risk limb.
• Anticoagulated patients: spontaneous haematoma can cause compartment syndrome; reverse anticoagulation as indicated.
• Kidney impairment: avoid NSAIDs and nephrotoxic antibiotics, and watch fluid balance.