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Breaking News: Ocular Sonography Detects Intracranial Pressure

SoRelle, Ruth MPH

doi: 10.1097/01.EEM.0000418673.41848.5c
Breaking News


Faced with a patient in the emergency department who might have increased intracranial pressure, Kristi Koenig, MD, reaches for one of her most valuable tools — the ultrasound machine — to rule out the possibility that forces are building inside the skull.

Dr. Koenig, the director of the Center for Disaster Medical Services and a professor of emergency medicine at the University of California, Irvine, School of Medicine, said ultrasound is a powerful tool for diagnosis in the emergency department. “In this case,” she said, “we can rule out elevated intracranial pressure. The ultrasound is a tremendous -triage tool with high sensitivity to detect people who need more monitoring.”

A recent study in Intensive Care Medicine confirmed that ultrasonography of the optic nerve sheath diameter is a good way to detect raised intracranial pressure. (2011;37[7]:1059.) That meta-analysis by Julie Dubourg, MD, and her colleagues of Hospices Civils de Lyon, Université Claude Bernard Lyon in France, pooled six studies, a total of 231 patients, and compared ultrasonography with intracranial pressure monitoring. They concluded that a positive test was associated with a 51 times higher risk of intracranial hypertension.

“[U]ltrasonography of ONSD [ocular nerve sheath diameter] shows a good level of diagnostic accuracy to detect intracranial hypertension in adult patients with TBI and intracranial hemorrhage,” the authors wrote. “In clinical decision-making, this technique may help physicians decide to transfer patients to specialized centers or to place an invasive device when specific recommendations for this placement do not exist.”

The French study's findings were supported by a pilot study by Robert Major, DipIMC (RCSEd), and colleagues at Norfolk and Norwich University Hospital and the Cambridge University Hospitals NHS Foundation Trust in the United Kingdom. That prospective study of 26 patients showed that ultrasound measurement of ONSD is sensitive and specific for raised ICP in the emergency department. (Emerg Med J 2011;28[8]:679.)

Dr. Koenig pointed out that use of ultrasound can be valuable when resources are limited. “Even at a Level I trauma center, when you have multiple patients waiting for a head CT, we need to know who we should be most concerned about and who needs to go to the operating room immediately. This helps us decide who needs to go first,” she said.

Ultrasonography also helps clinicians decide which injuries are the most dangerous to a person with multiple traumas, she said. Do you need to take the patient to the operating room immediately to control internal hemorrhaging or does that person need a quick head CT first?

“It makes sense that this would be valuable, and it should be relatively easy to train people to do it,” Dr. Koenig said. “You don't have to get a new piece of equipment. Most modern emergency -departments are going to have an ultrasound already. It just means adding this to the curriculum of basic things we teach.”

UC Irvine, like other medical schools around the country, is making ultrasound an important part of education, and medical students in the emergency department are learning to use ultrasound in a variety of settings, she said.

That push is the brainchild of J. Christian Fox, MD, a clinical professor of emergency medicine at UC Irvine and the assistant director of the emergency ultrasound program there. “Eighty percent of my life is spent teaching medical students ultrasound,” he said, where use of the technology is integrated into the physical exam portion of the medical school curriculum. “At the end of the second year, they get 25 hours of hands-on ultrasound practice and 20 hours of didactic, all given online through iTunes University.”

The measurement of ocular nerve sheath diameter to detect raised intracranial pressure is one of the techniques taught along with ultrasounds of extremities, heart, head, and neck, Dr. Fox said. “They are given their ultrasound machines to carry with them in the third year. They can take it home with them and practice on their friends if they want.”

Students can choose to take a more applied ultrasound course in the area of medicine in which they plan to concentrate; those planning to enter emergency medicine can do a month of emergency ultrasound, he said. “It makes sense that we teach this to medical students early,” Dr. Fox said. “When they go into residency, they end up being true experts in ultrasound.”

Using ultrasound is a natural evolution of medical practice, he said. In the time of Hippocrates, patients came in with abdominal pain and the physician put his hands on them to find out about the pain. The stethoscope allowed them to listen, and now ultrasound allows them to see.

Ultrasound in the emergency department makes even more sense. “Emergency physicians are incentivized to do as many CTs as possible,” Dr. Fox noted. “It's faster and enables them to see more patients per hour. They spend less time at the bedside and make more money. In addition, the CT allows us to share responsibility with another physician, and patients think they are getting the best care.”

That, however, ignores the risk of increased radiation, he said. Dr. Fox said he still orders CTs when they are warranted, but that he likes to go to the bedside with the ultrasound and spend more time with the patient. “I stand there and talk to the patient. It does slow me down, but it also enables me to image lightly and not involve radiation. Many times, I can get the answer to a whole host of pathologies,” Dr. Fox said.

The downside is that ultrasound requires skill and training, often more than can be obtained in the typical two-day course, he said. Two-day courses have their place, Dr. Fox said, in that they can encourage physicians to seek more training.

Some specialties criticize putting ultrasound in the hands of emergency physicians, but Dr. Fox said the pendulum has swung. “Not integrating it into practice is irresponsible,” he said.

The evidence is strong that ultrasound can detect intracranial pressure from optic sheath diameter, Dr. Fox said. “We are still working out the exact technique to minimize interobserver -reliability. We are almost there.”

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