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Extremity Vascular Injuries
1
What is the pathophysiology of extremity vascular injury?
Peripheral arteries are composed of three layers: outer adventitia, central muscular, and inner endothelial, or intima. Trauma, either blunt or penetrating, can produce hemorrhage (from laceration or puncture), thrombosis (from intimal disruption and exposure of the subendothelial matrix), or spasm—either alone or in combination. The intima is the least compliant of the vascular layers, and it fractures when the more flexible layers bend when deformed by an adjacent broken bone or joint dislocation. The injured intima may form a flap that can prolapse into the arterial lumen as a result of the forward blood flow dissecting under it. Penetrating injuries produce focal injury, while blunt injuries tend to be diffuse and injure not only the vascular structures but also the adjacent bone, muscle, and nerves. This adjacent tissue contains small, unnamed vessels or collaterals that are often injured in diffuse blunt trauma, thus exaggerating any existing ischemia. Transection of a vessel causes it to retract in spasm, which usually stops or reduces bleeding, but results in a hematoma, sometimes of large proportions. Puncture of an artery produces hemorrhage and a large hematoma, eventually tamponaded by surrounding tissue, but producing a pseudoaneurysm. Intimal prolapse may produce dissection and eventual thrombosis. Finally, injury to an artery and a vein in close proximity produces a local hematoma and eventually a pathologic connection between them—an arteriovenous fistula. These pathologies (hemorrhage, ischemia, thrombosis, pseudoaneurysm, and arteriovenous fistula) and their consequences should be considered in the diagnosis as one approaches a patient with extremity vascular injury.
2
Which are the most commonly injured arteries in the upper and lower extremity?
In the upper extremity, the brachial artery is most frequently injured, primarily because of its length and relative exposure to harm. The forearm arteries (radial and ulnar) are next most common, followed by the axillary and the subclavian. In the lower extremity, the most frequently injured artery is the superficial femoral, followed by the popliteal. The leg arteries (tibials and peroneal) and the common femoral are infrequently injured.
3
What orthopedic injuries commonly have associated vascular injuries?
There are several orthopedic injuries that mandate an arterial assessment because they are associated with arterial injuries, which, not infrequently, are missed. These are a supracondylar fracture of the humerus, an anterior or posterior dislocation of the knee and midshaft, or a supracondylar fracture of the femur.
4
How does one proceed with the evaluation of a patient with suspected vascular injury of the extremity? What are the physical findings or signs of vascular injury?
As with every trauma patient, the sequence follows that prescribed by the Advanced Trauma Life Support program. If the patient is in shock or extremis, treatment precedes evaluation. It is imperative that patients in shock are resuscitated to the endpoint of a palpable peripheral pulse in an uninjured extremity. If possible, the following information (obtained from the patient and/or prehospital providers) is helpful in managing a patients with a potential vascular injury: time of injury, amount of blood loss visible at the scene, mechanism of injury, initial vital signs, and trends in vital signs. After the primary survey is completed, the secondary survey for extremity arterial injury must include the following (for both the injured and uninjured extremity for comparison): neurologic exam (including motor and sensory), proximal and distal pulse examination, and assessment of capillary refill. The “hard” signs (in this context “hard” does not mean difficult to ascertain, but firm or solid) of vascular injury are pulsatile bleeding, expanding hematoma, palpable thrill, audible bruit (assessed distal to the injury), and evidence of regional ischemia (the six Ps: pain, pallor, poikilothermia, paralysis, paresthesia, and pulselessness). One might think of the acronym “hard” as h ardly a r easonable d oubt that a vascular injury is present. “Soft” signs are less firm and suggest the presence of a vascular injury: diminished but present pulse (diminished compared to the uninjured extremity), large but stable hematoma, injury to a peripheral nerve that is anatomically adjacent to a major artery, penetrating wound in the proximity of a major extremity artery, and history of moderate blood loss. The presence of “hard” signs reliably indicates the need for surgical therapy. The presence of “soft” signs indicates the need for additional diagnostics.
5
What diagnostic measures should be pursued when “soft” signs are present?
In addition to a well-done repeat secondary survey (see above), in the presence of a reduced or diminished pulse (compared to the uninjured limb in a resuscitated patient), one must perform an arterial pressure (systolic) index (API) comparing the injured limb to the uninjured limb. This is done using an appropriately sized sphygmomanometer cuff and a continuous wave (handheld Doppler device). The cuff should be placed just above the site of the injury. An artery distal to the injury is interrogated with the Doppler transducer, and the cuff slowly inflated until the Doppler signal can no longer be heard. The pressure at which the signal disappears as the cuff is slowly inflated is recorded and compared to the uninjured extremity with the cuff in a similar position. Using the systolic pressure in the injured limb as the numerator and the systolic pressure in the uninjured limb as the denominator, the API is calculated. An API of >0.9 can reliably rule out an arterial injury (API of <0.9 has a sensitivity of 95% and specificity of 97% for major arterial injury; an API >0.9 has a negative predictive value of 99%). However, repeated follow-up is strongly advised. For the other “soft” signs, imaging is necessary and is best done with a computed tomography (CT) arteriogram, which, for several reasons, has replaced catheter-based arteriography. Catheter-based arteriography can itself produce an arterial injury. Arteriography, at best, can provide biplanar or oblique images that are certainly helpful, but they may still miss occult injuries and definitely increase the dye load. CT angiograms require only a single venous dye injection and can provide not only coronal, sagittal, and axial views but also three-dimensional reconstructions that can be rotated and magnified to better view an area of interest. CT angiograms are less costly and can be performed much more quickly than catheter-based arteriography. The only potential limitation of CT angiography is the diffraction produced by metallic fragments that can overlie a possible injury.
6
What abnormalities on CT angiography determine a positive test result?
The following are considered to be “positive” findings: obstruction of flow, extravasation of contrast, early venous filling (suggesting arteriovenous fistula), contrast in a contained hematoma (pseudoaneurysm), intimal defect, and focal narrowing (spasm). It is absolutely imperative that the surgeon caring for the patient carefully review the images because what the radiologist reports may not have clinical significance. For example, obstruction of flow in a branch of a major nutrient artery (such as the profunda femoris) will not be symptomatic nor should it be treated. Other examples include the intimal defect, which can heal without producing symptoms, and spasm, which will usually resolve with simple observation.
7
What is the most effective way to control arterial bleeding in an injured extremity?
In the prehospital arena and in the emergency room, hemorrhage is best controlled with a correctly applied tourniquet. If not correctly applied, it will not control hemorrhage. If loosely applied, arterial flow continues, but the loose tourniquet obstructs venous outflow, thereby increasing hemorrhage. Attempts at controlling bleeding in the emergency room by the direct application of clamps is discouraged as a misplaced clamp can further damage the artery or an adjacent nerve.
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