Written by: Emma Greever (NUEM ’25) Edited by: Maurice Hajjar, MD (NUEM ’22)
Expert Commentary by: John Bailitz, MD
Welcome to the NUEM SonoPro Tips and Tricks Series where Local and National Sono Experts team up to take you scanning from good to great for a particular diagnosis or procedure.
For those new to the probe, we recommend first reviewing the basics in the incredible FOAMed Introduction to Bedside Ultrasound Book, 5 Minute Sono, and POCUS Atlas. Once you’ve got the basics beat, then read on to learn how to start scanning like a Pro!
Did You Know?
Ocular ultrasound is a quick procedure which can be done at the bedside to help differentiate between various ophthalmologic emergencies including retinal detachment, vitreous detachment, vitreous hemorrhage, lens detachment, and presence of foreign bodies. Indications for ocular ultrasound include eye pain, acute changes in vision, eye trauma, and suspicion of elevated intracranial pressure, or if there is swelling of periorbital tissue that inhibits direct visualization of the eye. The one absolute contraindication for ocular ultrasound is any suspicion for globe rupture, as placing any pressure on the globe can worsen extrusion of intraocular contents.
Ocular ultrasound can also be used to evaluate for elevated intracranial pressure (ICP). The optic nerve sheath communicates directly with the subarachnoid space. Cerebrospinal fluid flows between the intracranial space and orbit within the subarachnoid space; therefore, increased intracranial pressure is transmitted to the optic nerve sheath. Elevation of ICP is reflected by dilation of the optic nerve sheath. This can be quantified by measuring optic nerve sheath diameter (ONSD). Dilation of the optic nerve sheath often occurs with anterior bulging of the optic disc, seen as optic disc elevation (ODE) on ultrasound. Bulging of the optic disc is seen as papilledema on fundoscopic exam. Both ONSD and ODE measurements are ways to assess for elevated ICP.
If there is concern for elevated ICP, it is not always possible to do a dilated fundoscopic exam, invasive monitoring, or other imaging such as a CT. Point of care ultrasound (POCUS) allows for quick evaluation. Furthermore, POCUS allows for monitoring dynamic changes in ICP as doing serial fundoscopic exams and CTs is not feasible. It is also less invasive than other intra-cranial monitoring. When comparing ONSD (with a cut-off value of >5 mm) with findings of increased ICP on CT, sensitivity and specificity are 95.6% and 92.3%, respectively.
Beyond the emergency department, where else can a SonoPro scan for increased ICP?:
Aside from patients in the emergency department, POCUS for elevated ICP can be used in critically ill children in the PICU, adults in the Neurocritical ICU, and on the battlefield with handheld ultrasounds in combat medicine. ONSD changes within minutes of ICP changing. Studies have demonstrated that the change in ONSD or ODE is strongly correlated with changes in ICP, implying that POCUS could be used to dynamically detect real-time changes in ICP. In neuro-critically ill children, POCUS cannot replace invasive ICP monitoring but can be used as a screening tool in the ICU for intermittent monitoring of ICP when invasive methods are unavailable. It can allow for accurate dynamic evaluation of ICP, which is important in children with traumatic brain injury as fluctuations are common. Additionally, POCUS can be used in many different environments in which imaging is not readily available, such as on the battlefield or in-flight.
How to scan like a Pro:
Place the head of the bed at 45 degrees.
Apply a large, waterproof transparent film dressing (such as a Tegaderm) over the eye you are going to ultrasound, making sure the eye is closed. Make sure to get as much air out from under the Tegaderm as you can.
Apply a large amount of water-soluble ultrasound gel on top of the dressing.
Using a high-frequency linear probe set to ocular mode, place the probe over the eye with the indicator to the patient’s right. It is important to use very minimal pressure on the eye. To have control over the probe and to be able to make small movements with minimal pressure on the eye, rest the side of your hand on the patient’s cheek or bridge of the nose to stabilize your hand.
Ensure the probe is oriented in the transverse plane.
Tell the patient to look straight forward, to the left or right, up, or down as needed to obtain the best view.
Be sure to scan both eyes when concerned for elevated ICP.
What to Look For:
Identify the following structures: anterior chamber, lens, vitreous, retina, and optic nerve.
Use the rule of 3x5 to measure optic nerve sheath diameter:
Find the posterior aspect of the globe overlying the optic nerve
From that point measure 3 mm posteriorly (point A)
Maximal sheath distension occurs at 3 mm behind the papilla
Measure the diameter of the optic nerve from the second point (point B, 3 mm deep)
Measure from outer wall to outer wall
< 5mm is normal, 5-6 mm is indeterminate, >6 mm is elevated
Assess for papilledema – measure optic disc elevation (ODE)
Measure area between the fundus and dome of the papilla
ODE >0.6 mm predicts presence of fundoscopic optic disc edema (sensitivity 82%, specificity 76%); if using the threshold of 1.00 mm then sensitivity is 73% and specificity 100%
This sign can take a couple days to develop and may not appear at the same time as elevated ocular disc diameter
How to interpret:
Determine if ICP is elevated:
< 5 mm = Likely normal ICP
>6 mm = Indicates elevated ICP
Many causes of this, next steps are to identify what is causing the elevation in ICP
5-6 mm = Indeterminate range
If elevated, further evaluation for etiology of elevated ICP and treatment of cause.
If indeterminate, assessing for papilledema by measuring the ODE can help in the indeterminate range, although absence of papilledema does not indicate normal ICP.
It is important to note that there is significant variation from person to person regarding ONSD. In other words, >6 mm does not necessarily indicate increased diameter and <5mm does not necessarily mean normal. The SonoPro must use clinical judgement while assessing the ONSD.
Where to Learn More (References)
Where to Learn More (Hyperlinked References):
https://coreem.net/core/ocular-ultrasound/
https://www.coreultrasound.com/onsd/
https://emcrit.org/pulmcrit/pulmcrit-algorithm-diagnosing-icp-elevation-ocular-sonography/
Lin JJ, Chen AE, Lin EE, Hsia SH, Chiang MC, Lin KL. Point-of-care ultrasound of optic nerve sheath diameter to detect intracranial pressure in neurocritically ill children - A narrative review. Biomed J. 2020;43(3):231-239. doi:10.1016/j.bj.2020.04.006
Richards E, Mathew D. Optic Nerve Sheath Ultrasound. [Updated 2021 Jul 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022 Jan. Available from: https://www.ncbi.nlm.nih.gov/books/NBK554479/
Teismann N, Lenaghan P, Nolan R, Stein J, Green A. Point-of-care ocular ultrasound to detect optic disc swelling. Acad Emerg Med. 2013 Sep;20(9):920-5. doi: 10.1111/acem.12206. PMID: 24050798.
Expert Commentary
Thank you for providing this outstanding NUEM Blog Post! Ocular ultrasound for ICP has been a hot topic for over a decade in the EM, PEM, and ICU POCUS literature.
For a full review of my approach to ocular ultrasound, please refer to our 2018 Post - Ocular Ultrasound: From Floaters to Fogginess!
Since that post ,additional literature has been posted questioning the need for Tegaderms over the eye for the reasons we discussed in 2018. Bottomline, if the patient is reliable and can keep their eyes closed for five minutes, then you can skip the Tegaderm. But when the patient is less reliable, then the extra step may still make sense. When locating and measuring the Optic Nerve Sheath (ONS), be absolutely sure to stabilize your hand on the patient's face or forehead particularly when you are over-caffeinated or tired. Then be careful to rock the probe about 15 degrees laterally (illustrated here) to visualize the ONS parallel to the probe’s center US beams, and thereby avoid any edge artifact from visualizing at an angle. Even with the best technique, our local teaching, clinical use, and pilot research has consistently confirmed the need for obtaining multiple measurements of the small optic nerve sheath. Then averaging the best three to obtain the most accurate measurement.
Thank You Dr. Greever (NUEM ’25) and Dr. Hajjar, MD (NUEM ’22) for helping to improve patient care and MedEd through POCUS! Happy scanning everyone.
John Bailitz, MD
Vice Chair for Academics, Department of Emergency Medicine
Professor of Emergency Medicine, Feinberg School of Medicine
Northwestern Memorial Hospital
How To Cite This Post:
[Peer-Reviewed, Web Publication] Greever, E. Hajjar, M. (2024, Sep 11). Sono Pro Tips and Tricks for Evaluation of Elevated Intracranial Pressure. [NUEM Blog. Expert Commentary by Bailitz, J]. Retrieved from http://www.nuemblog.com/blog/sonopro-tips-and-tricks-for-evaluation-of-elevated-intracranial-pressure
