Bedside Ultrasound Shows Promise in Diagnosing Increased ICP

Nicola M. Parry, DVM

November 18, 2019

Use of bedside optic nerve ultrasonography may hold promise for diagnosing increased intracranial pressure (ICP) in children and adults, a systematic review and meta-analysis published online November 18 in Annals of Internal Medicine has shown.

"A normal sheath diameter measurement has high sensitivity and a low negative likelihood ratio that may rule out increased intracranial pressure," write Alex Koziarz, MSc, from the University of Toronto, Ontario, Canada, and colleagues, "whereas an elevated measurement, characterized by a high specificity and positive likelihood ratio, may indicate increased intracranial pressure and the need for additional confirmatory tests."

In cases of increased ICP, a patient's prognosis depends on prompt diagnosis to expedite ICP reduction and reduce associated morbidity and mortality.

Although various techniques are used to diagnose increased ICP, optic nerve ultrasonography (optic nerve sheath diameter sonography) is emerging as a rapid, noninvasive alternative in these cases.

However, use of this method remains predominantly limited to clinical research settings.

Additionally, studies to evaluate this technique have typically focused on specific patient populations and included only small numbers of patients.

With this in mind, Koziarz and colleagues conducted a systematic review and meta-analysis to examine the accuracy of optic nerve ultrasonography for diagnosing increased ICP in children and adults.

They analyzed 71 prospective diagnostic test studies (61 of which were conducted in adults) involving 4551 patients (4195 adults).

Of these 71 studies, 18 included patients with traumatic brain injury, 26 included those with nontraumatic brain injury, and 27 included mixed populations of patients.

Overall, optic nerve ultrasound accurately detected increased ICP in children and adults, including among patients with traumatic and nontraumatic causes of the condition.

For patients presenting with suspected traumatic brain injury, the researchers found a pooled sensitivity of optic nerve ultrasonography for identifying increased ICP of 97% (95% CI, 92% - 99%) and a specificity of 86% (95% CI, 74% - 93%). These patients were 6.93 (95% CI, 3.55 - 13.54) times more likely to have increased ICP after a positive result on optic nerve ultrasonography. And the corresponding negative likelihood ratio was 0.04 (95% CI, 0.02 - 0.10).

For those with suspected nontraumatic brain injury, sensitivity was 92% (95% CI, 86% - 96%) and specificity was 86% (95% CI, 77% - 92%). Similarly, these patients were 6.39 (95% CI, 3.77 to 10.84) times more likely to have increased ICP after a positive result on ultrasonography. The negative likelihood ratio for this patient population was 0.09 (95% CI, 0.05 - 0.17).

Estimates of the accuracy of optic nerve ultrasonography were similar among studies stratified according to patient age, clinician specialty and sonography training level, reference standard, sonographer blinding status, and cutoff value.

As they reviewed the literature for their study, Koziarz and colleagues also compared cutoff values and calculation methods for optic nerve sheath dilation on ultrasonography for identifying increased ICP. As a result, they established that a measurement of 5.0 mm may indicate increased ICP.

The authors acknowledge the limitations of their study, especially its inclusion of studies that were predominantly small, used different reference standards, and did not assess the effect of optic nerve ultrasonography on clinical outcomes.

Nevertheless, Koziarz and colleagues conclude that this method is "easy-to-use and can enable healthcare professionals to triage patients with suspected increased intracranial pressure."

In an accompanying editorial, Kathleen Y. Ogle, MD, from George Washington University Hospital, Washington, DC, and Resa E. Lewiss, MD, from Thomas Jefferson University Hospital, Philadelphia, Pennsylvania, applaud the careful methods used in the study.

However, they advise clinicians to use caution when interpreting the cutoff measurement.

"The measurement of the optic nerve sheath diameter is riddled with greater challenges than other bedside ultrasonography clinical applications," they stress.

But because this technique can undoubtedly reduce the time to appropriate management, the editorialists suggest future research should aim to establish a standardized protocol for using optic nerve ultrasonography.

They also encourage development of a cutoff for an ocular nerve sheath diameter measurement that accounts for sex and intersectional characteristics.

Anticipating that tele-ultrasound practice will continue to become increasingly available, Ogle and Lewiss also conclude that after an agreed cutoff and protocol are established, "novice sonographer–clinicians could be supported by ultrasound experts for remote integration of bedside ultrasonography."

Ann Intern Med. Published online November 18, 2019. Abstract, Editorial

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