All posts by TheTraumaPro

How Does That Work?: Angioembolization Coils

Ever wonder how interventional radiologists stop bleeding? They are very skilled in getting access to complicated areas of the arterial tree. Once they have located a bleeding point, they’ve got to plug it up with something.

Over the years, a wide variety of things have been used. They include blood clot, tiny metal or plastic spheres, superglue, and a variety of other creative things. One of the more recent additions is the metal coil.

On xray, these look like little pieces of piano wire in various shapes after they are inserted. But how do they work? They’re metal, and fairly smooth. How does that promote fast clotting?

The answer is more obvious when you look at one of these before it’s been inserted. Note the “fuzz”. These are synthetic fibers that are wrapped into the coil itself, and they are what actually promote clotting when the coil is in place.

Why Do They Call It: Extra-axial Blood?

You’ve seen it on head CT reports. “The patient has a collection of extra-axial blood…” Then it goes on to describe the location and size of a subdural hematoma. But why is it called “extra-axial?”

The answer lies in the embryology of the central nervous system. Yes, it’s been a long time since any of us have read anything about that. Early animals had a straight neural tube, which slowly evolved into a brain and spinal cord. This is known as the axis of the nervous system.

The brains of early vertebrates developed at the end of the neural tube, and were oriented in the same longitudinal axis as the rest of it. As brains got bigger, a 90 degree bend occurred at the cephalic flexure.

So in humans, there is a difference between the body axis and the brain axis. But the brain axis is what really counts. This means that any blood outside of the brain axis is defined as extra-axial.

Bottom line: Extra-axial blood is defined as any bleeding outside of the brain parenchyma. This includes subdural and epidural hematomas, and subarachnoid hemorrhage. It does not include any intraparenchymal bleeding like contusions or hematomas.

Lab Values From Intraosseous Blood

The intraosseous access device (IO) has been a lifesaver by providing vascular access in patients who are difficult IV sticks. In some cases, it is even difficult to draw blood in these patients by a direct venipuncture. So is it okay to send IO blood to the lab for analysis during a trauma resuscitation?

A study using 10 volunteers was published last year (imagine volunteering to have an IO needle placed)! All IO devices were inserted in the proximal humerus. Here is a summary of the results comparing IO and IV blood:

  • Hemoglobin / hematocrit – good correlation
  • White blood cell count – no correlation
  • Platelet count – no correlation
  • Sodium – no correlation but within 5% of IV value
  • Potassium – no correlation
  • Choloride – good correlation
  • Serum CO2 – no correlation
  • Calcium – no correlation but within 10% of IV value
  • Glucose – good correlation
  • BUN / Creatinine – good correlation

Bottom line: Intraosseous blood can be used if blood from arterial or venous puncture is not available. Discarding the first 2cc of marrow aspirated improves the accuracy of the lab results obtained. The important tests (hemoglobin/hematocrit, glucose) are reasonably accurate, as are Na, Cl, BUN, and creatinine. The use of IO blood for type and cross is not yet widely accepted by blood banks, but can be used until other blood is available.

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Reference: A new study of intraosseous blood for laboratory analysis. Arch Path Lab Med 134(9):1253-1260, 2010.

Can Lead Poisoning Occur After A Gunshot?

This is a fairly common question from victims of gunshots and their families. As you know, bullets are routinely left in place unless they are superficial. It may cause more damage to try to extract one, especially if it has come to rest in a deep location. But is there danger in leaving the bullet alone?

One of the classic papers on this topic was published in 1982 by Erwin Thal at Parkland Hospital in Dallas. The paper recounted a series of 16 patients who had developed signs and symptoms of lead poisoning (plumbism) after a gunshot or shotgun injury. The common thread in these cases was that the injury involved a joint or bursa near a joint. In some cases the missile passed through the joint/bursa but came to rest nearby, and a synovial pseudocyst formed which included the piece of lead. The joint fluid bathing the projectile caused lead to leach into the circulation.

The patients in the Parkland paper developed symptoms anywhere from 3 days to 40 years after injury. As is the case with plumbism, symptoms were variable and nonspecific. Patients presented with abdominal pain, anemia, cognitive problems, renal dysfunction and seizures to name a few.

Bottom line: Any patient with a bullet or lead shot that is located in or near a joint or bursa should have the missile(s) promptly and surgically removed. Any lead that has come to rest within the GI tract (particularly the stomach) must be removed as well. If a patient presents with odd symptoms and has a history of a retained bullet, obtain a toxicology consult and begin a workup for lead poisoning. If levels are elevated, the missile must be extracted. Chelation therapy should be started preop because manipulation of the site may further increase lead levels. The missile and any stained tissues or pseudocyst must be removed in their entirety.

Reference: Lead poisoning from retained bullets. Ann Surg 195(3):305-313, 1982.

Pneumothorax: How Big Is Too Big?

One of the big unanswered questions in the management of pneumothorax is, how big is too big? At what size is a chest tube of some type mandatory? 

The problem is that we just don’t have any good data. Seems like a simple problem, right? Unfortunately, it’s not. A pneumothorax is a three dimensional collection that surrounds the lung in very random ways. All we had to detect and “measure” them for decades was the lowly chest x-ray. Unfortunately, this is a 2D shadow picture that does not allow us to accurately estimate the size.

A few old papers exist that tried to quantify pneumothorax, but they are of no use now that we have chest CT. Unfortunately this new technology has drawbacks, as well. First, it’s just a stack of 2D images that our minds assemble into a 3D mental model, so it’s still difficult to quantify the air. And second, you shouldn’t be getting a chest CT just to diagnose pneumothorax. In blunt trauma, it’s really just for checking the thoracic aorta for injury.

So we’re left with the original question, and there are three answers. If there is any physiologic compromise (hypoxia, tachypnea, anxiety), then the chest should be drained. If the pneumothorax is enlarging over serial chest x-rays, then it should be drained before it causes physiologic change. And finally, if there is concern that it is so large that it will take too long to absorb, especially in older patients with comorbidities, a chest drain should be inserted. This is a somewhat soft indication, however.

Bottom line: The three reasons above are the usual answers to the question, “how big is too big?” For me, once the pneumothorax pushes the lung 1-2 cm away from the chest wall from apex to base, it’s time for a tube.

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