You start your day in the usual fashion, completing your aircraft check and eating breakfast with the rest of the crew. Your pilot provides a brief for the team, including your nursing student ride-along. Given the sunshine and perfect temperatures, you pull your aircraft outside and settle in for your first request.
It doesn’t take long to get sent on a scene run. Launching for the 5-minute flight, the communication center chimes into your ear.
“You’re intercepting for an unknown unresponsive 55-year-old male.”
You and your partner throw out some differentials. "Seizure, overdose, maybe an MI or stroke?” Before completing your list, you’re landing assured and touching down in a school parking lot.
Opening the doors reveals a dual Paramedic crew ventilating a freshly intubated patient.
“This is Alan; he’s 55. We arrived on the scene and found him slumped over on the couch with significant secretions and snoring respirations. He was quite hypertensive, 196/80, and tachycardic at a rate of 106. We intubated him with Rocuronium and Etomidate, placing the ETT without any hypoxic episodes.”
The differential remains fairly broad. You ask some additional questions and find no signs of drug paraphernalia on the scene. His blood glucose returns at 106 mg/dL.
Your partner places the patient on your monitor as you start up your ventilator and provide some analgesia & sedation.
Soon, you’re departing the scene for a 25-minute flight to the large academic hospital. Given the undifferentiated nature of your patient, you pull out your ultrasound probe and begin scanning. No free fluid in the abdomen, the cardiac squeeze looks pretty darn good, no B-Lines in either lungs. Next, you pull out a tegaderm and place it over the patient's eye, moving the probe into position. The nursing student pipes up and asks, “what the heck are you looking at the eye for.”
Ocular point of care ultrasound (POCUS) has gained popularity within Emergency Medicine, given its high sensitivity, specificity, and ease of examination. Various pathologies can be examined, ranging from the foreign body to lens dislocation. One area that can provide incredible benefit to EMS is its utilization to assess for states of increased intracranial pressure.
How does it work? The optic nerve, an easily assessable location with POCUS, can be “thought of as an outpouching of intact brain tissue…” (1). Below you’ll find a brief refresher on eye anatomy so we can easily translate it to our ultrasound view.
The cool part is the sensitivity and specificity behind this exam.
It seems pretty straightforward, but what group of patients should we perform this scan in? The primary indication for EMS will be groups where high ICP is suspected.
Contraindications-wise, globe rupture/eye injury patients should sway you away from this exam. Increased pressure on the eye, even slight, can worsen the injury.
Patient setup is fairly easy. First, placing a tegaderm over the eye often makes cleaning up easier. Gel application follows, applying a generous amount over the Tegaderm. The gel allows sound conduction into the eye without placing any direct pressure on the eyeball itself. This is key, especially in patients who cannot identify “too much” pressure, such as our intubated patient.
Place a linear probe in a transverse position across the eye, and you’ll acquire an image similar to the one below.
What exactly are we looking at?
Next, we’ll do some simple measurements. Our initial measurement will measure into the optic nerve, the second one across.
In the right context,>6 mm across (dotted line) can be associated with increased ICP. There is an awkward middle ground, between 5-6mm, and the examination is indeterminate. The blog referenced below by Pulmcrit offers some great suggestions for this middle ground (2).
Additional potency for this exam comes from the ability to repeat it. If you find you are with the patient for a decent length of time or have clinical changes, you can easily repeat this examination (or keep an eye on it!).
Where does this leave us with Alan? You complete your POCUS examination, noting >6 mm optic nerve sheath diameter. Within minutes his BP increases to over 200 systolic, now with periods of bradycardia. Concerned for herniation, you administer hypertonic saline and update the receiving facility with your concerns.
Have any cool POCUS saves or stories? Let us know!
1. Evan Richards; Sunil Munakomi; Dana Mathew. (n.d.). Optic Nerve Sheath Ultrasound. National Library of Medicine . Retrieved from https://www.ncbi.nlm.nih.gov/books/NBK554479/
2. Social MeJosh FarkasJosh is the creator of PulmCrit.org. He is an associate professor of Pulmonary and Critical Care Medicine at the University of Vermont. (2017, October 28). Pulmcrit: Algorithm for diagnosing ICP elevation with ocular sonography. EMCrit Project. Retrieved March 18, 2023, from https://emcrit.org/pulmcrit/pulmcrit-algorithm-diagnosing-icp-elevation-ocular-sonography/