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Search Still On for Noninvasive Methods to Monitor ICP

Sorelle, Ruth MPH

doi: 10.1097/01.EEM.0000616444.13324.40
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Despite an ongoing quest for noninvasive ways to monitor intracranial pressure, a recent meta-analysis of various methods found that none provides a dependable diagnosis.

Physical exam, CT, sonography of the optic nerve sheath diameter, and the transcranial Doppler pulsatility index all fell short of ruling out elevated ICP, according to the review. (BMJ. 2019;366:l4225; http://bit.ly/313VQL5.) Substantial midline shift could suggest elevated ICP, the researchers at the University of Ottawa said, but its absence does not rule it out.

Emergency physicians at the Ottawa Hospital in Canada said invasive monitoring gives the best estimation of intracranial pressure, and Shannon Fernando, MD, a fifth-year resident in emergency medicine and critical care at the university, added that good observational evidence shows that patients with elevated intracranial pressure on an invasive monitor are more likely to have poor outcomes.

That doesn't mean people shouldn't be monitored, of course. “We should use monitors whenever possible,” he said, “but there are downsides to monitoring.” A major one in the emergency department is when no neurosurgeon is available to put in the monitor, Dr. Fernando said, not to mention that the catheter itself can become infected or cause bleeding.

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Physical Signs

The Ottawa researchers looked at physical signs such as fixed and dilated pupils and posturing that could be symptomatic of elevated intracranial pressure in a meta-analysis of 40 studies. “We were looking for something reliable to tell physicians,” Dr. Fernando said. “We could not rely on the absence of a sign to rule out intracranial pressure. A patient without a blown pupil might still have increased pressure in the brain.”

The studies in the meta-analysis assessing optic nerve sheath diameter measured with ultrasound used cutoffs too variable to use it as a diagnostic tool, he said, and transcranial Doppler tests of arterial blood pressure show promise for diagnosing elevated intracranial pressure but have not been validated.

Another literature review several years ago by Helena Kristiansson, MD, and Emelie Nissborg, MD, of the University Hospital of Lund, found similar problems with noninvasive intracranial pressure monitoring, such as CT, MRI, transcranial Doppler, electroencephalography, and audiological and ophthalmological techniques. “None of the noninvasive techniques available today [is] suitable for continuous monitoring, and they cannot be a substitute for invasive monitoring,” they wrote. “They can, however, provide a reliable measurement of the ICP and be useful as screening methods in select patients, especially when invasive monitoring is contraindicated or unavailable.” (J Neurosurg Anesthesiol. 2013;25[4]:372.)

John Webster, PhD, and a group of bioengineers and neurosurgeons at the University of Wisconsin conducted a similar review with the same results. (Physiol Meas. 2017;38[8]:R143.) Their work was preliminary to possible development of new monitors that might be measurement tools to monitor ICP, said Dr. Webster. “We have the right way to go,” he said.

His method would include a small sensor and a valve implanted in the back of the head. “If the pressure gets too high, you open the valve and release the pressure,” Dr. Webster said. “Fluid flows down a catheter into the stomach. It's doable.”

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Better to Treat

In the meantime, the search for a usable noninvasive monitor continues, and using the invasive monitor continues to pose problems. Demetrios Demetriades, MD, and colleagues at the University of Southern California studied how Level I U.S. trauma centers used intracranial pressure monitors in patients with severe traumatic brain injuries. (Injury. 2017;48[9]:1944.) They found that compliance with the monitors' use as recommended by the Brain Trauma Foundation was low. “In this study, ICP monitoring was associated with poor outcomes, and was found to be an independent risk factor for mortality,” the authors wrote.

“Compliance with BTF guidelines was low, even in Level I trauma centers,” they concluded. “There is a need to re-evaluate current BTF guidelines and identify any specific groups with TBI that could benefit from ICP monitoring.”

Dr. Fernando said he was concerned about patients who are first seen in remote centers that lack the expertise and technology. “Even though all the signs are negative, there is little harm in treating for intracranial pressure,” he said. “Raise the head of the bed, treat pO2 with oxygen. Give an osmotic agent such as hypertonic saline or mannitol.”

“The risk of leaving someone with untreated ICP strongly exceeds the risk of giving treatment,” Dr. Fernando said. His study and others that have evaluated noninvasive and invasive measurements might lead to a clinical decision instrument that could involve different modalities and give the physician a roadmap for treatment, he said.

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Ms. SoRellehas been a medical and science writer for more than 40 years, previously at the University of Texas MD Anderson Cancer Center, the Houston Chronicle, and Baylor College of Medicine. She has received more than 60 awards, including the Texas Human Rights Foundation Award. She has been a contributor to EMN for more than 20 years.

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