- Crush injury is defined as injury due to compression of extremities or other parts of the body that causes muscle swelling or trauma, with or without neurological or orthopedic problems in the body parts. Body areas most commonly involved are the limbs and torso.
- Crush syndrome develops when crush injury is extensive and prolonged, causing systemic manifestations. These systemic effects are due to traumatic rhabdomyolysis (muscle breakdown) and reperfusion syndrome (release of potentially toxic muscle cell components and electrolytes into the circulatory system) after sudden release of pressure over the crushed limb or torso. Acute hypovolemia and metabolic abnormalities are common and can be severe (even fatal), and myoglobinuria from trauma to muscles frequently may cause or exacerbate renal failure if untreated.
- Crush injuries and crush syndrome in MWDs are expected after building collapses, most frequently after natural disasters or explosions. In humans, the incidence of crush syndrome is 2-15% with approximately 50% of those with crush syndrome developing acute renal failure. Of those with renal failure, 50% need dialysis. Crush syndrome is rarely reported in animals.
Pathophysiology
- Crush injury develops after muscle injury and muscle cell death. Three mechanisms are responsible for the death of muscle cells, to include direct cell lysis by the force of the crush; direct pressure on muscle cells causing muscle ischemia, development of anaerobic metabolism and lactic acidosis, and cell membrane disruption and leakage; and vascular compression or disruption, with loss of blood supply to muscle tissue.
- These mechanisms cause the injured muscle tissue to generate and release a number of substances that may be toxic in the general circulation. The crushing force actually serves as a protective mechanism, preventing these toxins from reaching the central circulation. Once the patient is extricated and the force is released, reperfusion injury is prevalent due to release of toxic compounds and reactive oxygen species. Reperfusion injury may continue for as long as 60 hours after release of the crush injury.
- Other consequences of reperfusion include massive third spacing of fluids in crushed tissues, leading to hypovolemia and shock and exacerbating renal injury, and leading to compartment syndrome.
Clinical Presentation
Clinical signs of crush injury/crush syndrome include some or all of the following:
- Skin injury of the affected body part (may be subtle and less impressive than other signs)
- Limb swelling (may be delayed)
- Paresis or paralysis (may be mistaken as spinal cord injury)
- Loss of sensation (may mask the severity of underlying injury)
- Pain (typically becomes severe with reperfusion)
- Absent or weak extremity pulses
- Discolored urine due to myoglobinuria or hematuria or both
- Hypotension due to hypovolemia (dehydration, hemorrhage, third spacing of fluids) is commonly present and may be severe
- Massive third spacing (often causes or exacerbates compartment syndrome and renal failure)
- Metabolic abnormalities (hypocalcemia, hyperkalemia, and lactic acidosis)
- Clinical signs of compartment syndrome (severe pain in the involved extremity, pain on passive stretching of the involved muscles, decreased sensation to the affected limb)
- Renal failure (due to rhabdomyolysis and secondary myoglobinuric acute tubular necrosis).
Patient Management
- Treat MWDs, if possible, before and during extrication.
- Maintain a high index of suspicion, as MWDs with crush injury may present initially with few signs or symptoms. Delayed treatment leads to poor outcome.
- Most crush syndrome patients have an extensive area of involvement such as a lower extremity and/or the pelvis. It requires more involvement than just one paw. Also, the crushing force must be present for some time before crush injury syndrome can occur.
- The syndrome may develop in <1 hour in a severe crush situation, but usually takes 4 to 6 hours of compression for the processes that cause crush injury syndrome to take place.
- The hallmark initial treatment for crush syndrome is IV fluid therapy before release of pressure and continued during extrication and evacuation. Place multiple IV lines, because the MWD will require large fluid volumes and there is a risk of catheter dislodgement during extrication. Normal saline is the initial fluid of choice. Avoid fluids with potassium.
- Once compression is removed, maintain aggressive fluid therapy. Specific guidelines for fluid volumes to administer are difficult to provide. As a starting point, use a rate of 3-5 mL/kg/hr to improve pulse quality, blood pressure (if possible to measure), CRT, and mentation. Try to estimate urine output – the goal is to maintain urine output >1-2 mL/kg/h.
- Alkalinization of the blood with bicarbonate (as is done for humans) is likely not going to be feasible. Thus, HCPs should focus on aggressive IV fluid therapy to correct dehydration and promote diuresis pending extrication and evacuation.
- Anticipate secondary complications. MWDs with crush injury should be treated initially as any other multiple trauma victim.
- Compartment syndrome is rare in dogs; this seems to be a much more common and more severe problem in humans, so extreme measures to control intracompartmental pressures like fasciotomy are unwarranted.
- Wounds should be cleaned and covered with sterile dressings in the usual fashion. Splint fractures if possible.
- Provide analgesia to any MWD with crush injury or crush syndrome (See CPG 16).