Compartment Syndrome and Fat Embolism

Medical-Surgical · Musculoskeletal / Orthopedics·Updated 2026-10-28

What it is

Compartment syndrome is rising pressure inside a closed muscle compartment, from swelling or bleeding within it or a tight cast or dressing around it. The pressure collapses capillaries, so muscles and nerves become ischemic and die within hours. Fat embolism syndrome follows long-bone and pelvic fractures, usually within 24 to 48 hours: fat globules from the marrow lodge in the capillaries of the lungs, brain and skin. Both are emergencies the nurse detects through frequent neurovascular and respiratory assessment.

What the NCLEX focuses on

Earliest and most reliable sign of compartment syndrome: pain out of proportion to the injury, unrelieved by opioids, and pain on passive stretch of the muscles in the compartment.
The 6 Ps: pain, pressure, paresthesia, pallor, paralysis and pulselessness; paralysis and pulselessness are late signs, so a palpable pulse does not rule it out.
Risk factors: tibia and forearm fractures, crush injuries, tight casts or dressings, and circumferential burns.
Muscle breakdown releases myoglobin: dark reddish-brown urine signals rhabdomyolysis and risk of acute kidney injury.
Fat embolism syndrome: sudden dyspnea, tachypnea, hypoxemia, restlessness or confusion, and petechiae over the chest, axillae and conjunctivae.
Early immobilization and surgical fixation of long-bone fractures reduce fat embolism; handle an unstable fracture as little as possible.
Unilateral calf swelling and warmth point to DVT instead; petechiae and confusion point to fat embolism.

Priority nursing actions

Perform neurovascular checks (pain, color, temperature, capillary refill, pulses, sensation, movement) and compare with the other limb.
At the first sign of compartment syndrome, keep the limb at heart level and loosen any constricting dressing.
Notify the provider immediately to bivalve or remove a cast and to measure compartment pressure; prepare for fasciotomy.
Monitor urine output and color for myoglobinuria.
For suspected fat embolism, raise the head of the bed, give high-flow oxygen, call the rapid response team and prepare for ventilatory support.

Numbers to know

Item	Value	Why it matters
Neurovascular checks after injury or casting	Every hour for the first 24 hours	Detects rising pressure early
Capillary refill	Less than 3 seconds	Slower refill signals poor perfusion
Limb position with suspected compartment syndrome	At heart level	Elevation lowers arterial inflow to the compartment
Irreversible muscle and nerve damage	Begins within 4 to 6 hours	Fasciotomy is time-critical
Fat embolism onset	Usually 24 to 48 hours after a long-bone fracture	Window for close respiratory and mental-status checks

Common exam traps

Choosing to elevate the limb on pillows above the heart: wrong because elevation reduces arterial perfusion into a compressed compartment.
Choosing to give more opioid and reassess later: wrong because pain unrelieved by opioids is the key early sign and needs immediate escalation.
Choosing to wait for a lost pulse: wrong because pulselessness is a late sign that appears after tissue damage.
Choosing anxiety as the cause of new confusion and tachypnea 2 days after a femur fracture: wrong because these are early fat embolism signs that need oxygen and rapid response.

What to teach

Report pain that worsens despite elevation and pain medicine, and any numbness, tingling, coldness, pallor or inability to move the fingers or toes.
Move the fingers or toes often, keep the cast dry, and never push objects inside the cast.
After a long-bone fracture, report shortness of breath, confusion, or a rash of tiny red-purple spots at once.

Client handout: Caring for Your Cast (nurse guide and printable patient handout).

Try 2 NCLEX-style questions on this topic

From the NCLEXPace question bank. Pick your answers, then check them inside NCLEXPace.

Question 1 · QID 08DD9600

A client with a lower leg cast reports pain that is significantly worse than expected for the injury, along with numbness and a cool, pale foot. Which condition should the nurse suspect?

Select the best answer.

A. Localized pressure irritation from the cast causing temporary discomfort and altered sensation without significant vascular compromise
B. Compartment syndrome
C. An acute anxiety response causing heightened pain perception, tingling, and subjective concern about circulation in the injured leg
D. Expected post-casting swelling and discomfort that commonly cause temporary numbness, coolness, and pallor during the first several hours

Question 2 · QID 2D8A93A3

The nurse cares for several clients on an orthopedic trauma unit.

For each assessment finding, click to specify the fracture complication it most likely indicates.

	Compartment syndrome	Fat embolism syndrome	Deep vein thrombosis	Rhabdomyolysis	Osteomyelitis
Pain on passive stretch of the fingers under a forearm cast
Confusion and chest petechiae 2 days after a femur fracture
One calf swollen, warm, and tender 8 days after a tibial fracture
Dark tea colored urine after a leg was pinned under a vehicle for 3 hours
Fever and purulent drainage from an open fracture wound 2 weeks after surgery

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Sources

Harding MM, Kwong J, Hagler D, Reinisch C. Lewis's Medical-Surgical Nursing: Assessment and Management of Clinical Problems. 12th ed. Elsevier; 2023; Chapter: Musculoskeletal Trauma and Orthopedic Surgery.
American Academy of Orthopaedic Surgeons. Management of Acute Compartment Syndrome: Evidence-Based Clinical Practice Guideline. AAOS; 2018.

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