Tag Archives: vascular

ABI vs API For Vascular Trauma

In general, the first maneuver in evaluating for possible vascular injury in an extremity is the good old physical exam. Is there a pulse or isn’t there? You can then subdivide that into: is the pulse weaker than normal. The problem is, what is “normal?” In most cases, we just compare it to another pulse somewhere and make a subjective judgment.

But we love to be more objective about things. Over the years, two simple, noninvasive techniques for evaluating pulses have been developed. The first is the ankle brachial index (ABI) , which was first described in 1930 and was used for diagnosis of peripheral vascular disease in 1950. It is performed by dividing the systolic pressure at the ankle of the affected extremity by the systolic pressure of one of the brachial arteries in the arms.

The new(er) kid on the block is the arterial pressure index (API), first described in 1991. This value is calculated by dividing the systolic pressure in the affected extremity by the systolic pressure in the contralateral uninjured extremity.

Many trauma professionals use the ABI when evaluating for potential vascular trauma. The typical threshold for pursuing further evaluation is 0.9, and several papers have been published on this topic. The API has also been critically evaluated, and the same threshold is used.

However, I believe that the API is more relevant and accurate than ABI. Why? Patients with atherosclerotic disease typically manifest it in their lower extremities. This serves to falsely elevate the ABI to a value greater than 1.0. It becomes more difficult to get down to that critical value of 0.9 that might indicate a vascular injury. Thus, the ABI may not detect a true injury, especially one in the lower extremities.

The API, on the other hand, relies on the fact that the amount of atherosclerotic disease is usually symmetric between the two lower extremities or the two upper extremities. Thus, the value will not be falsely elevated and will more accurately reflect the presence or absence of a vascular injury.

Bottom line: I recommend that you use the API when evaluating extremity vascular injury. Calculate the ratio by dividing the systolic pressure in the injured extremity with the pressure in the contralateral uninjured extremity (if there is one). A value < 0.9 indicates the need for angiographic evaluation, usually by CT scan.

And here’s a nice algorithm for managing peripheral vascular trauma from Life in the Fastlane:

Reference: Can Doppler Pressure Measurement Replace “Exclusion” Arteriography in the Diagnosis of Occult Extremity Arterial Trauma? Ann Surg 214(6):737-741, 1991.

Blunt Vertebral Artery Injury

Following up on yesterday’s post, I’ll deal with vertebral artery injuries today. These injuries are uncommon, making them hard to study and develop management recommendations. The literature suggests that about 1% of blunt trauma patients may sustain one of these. Most commonly, the method is motor vehicle crash, and just about any mechanism (hyperflexion, hyperextension, distraction injury, and facet fractures). Fracture of C1-3 has a higher association with the injury.

What is the natural history of this injury? If treated, 67% of occluded vessels recanalize, and 90% of stenotic arteries return to normal caliber. About 15% of untreated injuries will suffer a stroke. As seen in the paper cited yesterday, a good number of these are present on patient arrival and are nonpreventable. But the key issues are identifying an injury in the first place, and treating appropriately. Unfortunately, these are not straightforward.

Although the gold standard for detecting this lesion is digital subtraction angiography, no one does this in acute trauma patients anymore. CT angiography is well established, and the sensitivity rate approaches 99%. The main question is when to get it. To see my hospital’s interpretation of the literature, download our blunt imaging protocol below.

Treatment options include anticoagulation / antiplatelet therapy and endovascular therapy. There is much more experience with the former, but it can’t be used in patients at risk for bleeding (e.g. severe TBI). Unfractionated heparin is good for in-hospital use because it easily reversed. Longer term, anti-platelet agents are preferred. Aspirin is cheaper than clopidagrel, and no study has shown convincing superiority of one over the other. Determining whether endovascular stenting or embolization is necessary requires consultation with a neurosurgeon and interventional radiologist. The decision making is complex and not laid out in the literature. It’s flying by the seat of one’s pants, at best but can be a valuable adjunct.

Followup imaging is suggested to help determine when and if anti-platelet therapy can be discontinued. The best timing for these studies has not been worked out, but since these lesions tend to evolve over 7-10 days, any time after 2 weeks should be appropriate.

Bottom line: This is a tough topic because of the scarcity of good data, which in turn is due to the rarity of the injury. I believe that finding the lesions with good screening criteria offers the best chance of preventing complications such as stroke. Choice of management is best done in collaboration with your neurosurgical and radiologist colleagues.

Related posts:

Using CT To Diagnose Extremity Vascular Injury

The traditional gold standard for diagnosis of vascular injury to the extremities has been a good physical exam plus conventional catheter angiography. However, using angiography always adds a layer of complexity and risk to patient care. The interventional team may not be immediately available after hours, there is typically a road trip within the hospital to deliver the patient for the study, and overall it is quite expensive.

With the advancements we have seen in CT angio techniques and scanner technology, some centers have been using computed tomography to evaluate for vascular injury. A few small retrospective studies have been done, but this month a larger prospective study was published.

Over a 20 month period, 635 patients with extremity trauma and a suspicion for vascular injury were entered into the study. A structured physical exam was performed, and any patient with “hard signs” of vascular injury were taken to the OR. 527 patients had no signs of vascular injury and were observed and released. The remaining 73 (most had soft signs of vascular injury) underwent CT angiography of the extremity.

The sensitivity and specificity of this test were 82% and 92%, respectively. Positive and negative results were nearly perfectly predictive. However, approximately 10% were inconclusive, usually due to bullet artifact or reformatting errors. These patients either underwent confirmatory conventional angiography or operation.

Bottom line: Angiography using multi-detector CT scanners is an excellent tool for evaluating potential extremity vascular trauma from penetrating trauma. The technology is available around the clock without a wait, and usually does not involve lengthy trips through the hospital. A good physical exam is imperative so patients with hard signs of injury can go straight to the OR. Equivocal studies must be evaluated further by conventional angio or an operation.

Reference: Prospective multidetector computed tomography for extremity vascular trauma. J Trauma 70:808-815, 2011.

Splenic Vascular Blush

Contrast blush is always a concern when seen on CT of the abdomen for trauma. It can represent one of two things, and both are bad:

  • Active extravasation of contrast
  • Splenic pseudoaneurysm

These two clinical issues can be distinguished by looking at the location of the contrast and its persistence. A pseudoaneurysm is located within the parenchyma, and the contrast will wash away, so it will not be visible on delayed images. Contrast that extends beyond the parenchyma or persists in delayed views represents active bleeding. In either case, the failure rate of nonoperative management exceeds 80% in adults without additional measures being taken.

Clinically, these patients usually act as if they are losing volume and require additional crystalloid and/or blood transfusion. The natural history in adults is for bleeding to continue or for the pseudoaneurysm to rupture, resulting in a quick trip to the operating room.

If vital signs can be maintained with fluids and blood, a trip to interventional radiology may solve the problem. Selective or nonselective embolization can be carried out and patients with only a few bleeding points can be spared operation. However, if multiple bleeding areas are seen, it is probably better to head to the OR for splenorrhaphy or splenectomy.

The image below shows likely areas of extravasation. They are a bit large to be pseudoaneurysms.

Spleen Blush-CT

Children are different than adults. Extravasation from spleen injuries in prepubescent children frequently stops on its own. Angiography should only be used if the child is failing nonoperative management.