Position-Related Compartment Syndrome

Position related compartment syndrome is raised pressure within a closed fascial compartment from prolonged limb elevation, compression or hypoperfusion in the lithotomy, lateral, prone or head down position, leading to ischaemia of muscle and nerve.

Epidemiology. It is rare (about 1 in 3,500 to 1 in 8,700 lithotomy procedures longer than 4 hours; roughly 1 in 50,000 overall for leg compartment syndrome after surgery) with risk increasing at operative times over 4 hours. Limb loss and rhabdomyolysis are possible.

Risk factors. Operative time over 4 hours, lithotomy with legs high (Trendelenburg), obesity, muscular build, male sex, peripheral vascular disease, hypotension, vasopressors, leg compression devices, tight leg wraps, lateral position (dependent arm and leg), and prone position with an unpadded limb.

Pathophysiology.

Elevation of the limb reduces arterial perfusion pressure at the calf (about 0.78 mmHg/cm of height), while external compression and venous congestion raise compartment pressure. Reperfusion after reducing the legs causes oedema and a vicious cycle of ischaemia.

Pain out of proportion, aggravated by passive stretch of muscles, tense swollen compartment, paraesthesia, pallor, weakness and (late) pulselessness and paralysis. Regional or epidural anaesthesia may mask the pain. Bladder or kidney signs of rhabdomyolysis follow.

Red flags.

• Pain out of proportion or escalating analgesic need.
• Tense, swollen limb.
• Sensory loss or weakness.
• Dark urine and rising creatine kinase.

Clinical diagnosis. Measure compartment pressure with an invasive device if the diagnosis is uncertain or the patient cannot be examined: a pressure within 30 mmHg of diastolic pressure (delta pressure under 30 mmHg) or absolute pressure of 30 mmHg or more supports the diagnosis. Check creatine kinase, creatinine, potassium, myoglobin and lactate. Doppler is not reliable because pulses persist until late.

Differential diagnosis.

• Deep vein thrombosis.
• Cellulitis.
• Nerve injury.
• Arterial occlusion.
• Rhabdomyolysis without compartment syndrome.
• Block related deficit.

Remove external compression, lower the limb to heart level and release dressings. Maintain mean arterial pressure at 65 mmHg or more, and give 100% oxygen. Do not elevate the limb over heart level.

Emergency four compartment fasciotomy (calf) within 6 hours of onset is the definitive treatment, and delay increases limb loss. Leave wounds open and plan a delayed closure at 48 to 72 hours.

Rhabdomyolysis:

• Crystalloid: 1 to 2 L IV in the first hour, then 200 to 300 mL/h to keep urine output at 1 to 2 mL/kg/h; monitor creatine kinase, potassium, calcium and renal function; reduce in heart failure.
• Treat hyperkalaemia: calcium chloride 10% 10 mL IV, insulin 10 units with 25 g glucose IV, monitor ECG and glucose hourly.
• Haemodialysis for refractory hyperkalaemia, acidosis or anuria.

Prevention. Limit lithotomy time to under 4 hours, lower legs briefly every 2 hours in long cases, avoid prolonged extreme head down tilt, pad and avoid tight wraps, maintain blood pressure, use leg supports that allow calf freedom and monitor limbs in prolonged surgery.

Monitoring. Limb examination every 1 hour for the first 6 hours then every 4 hours, serial creatine kinase, creatinine and urine output.

Referral and escalation. Immediate orthopaedic or vascular surgical review. Nephrology and critical care for renal injury.