by Kaity Barker-Grasser, FNP

Ultrasound itself is not an unfamiliar technology to most, having been used in obstetrics and gynecology (OB/GYN) for many years. Newer research is now showing that ultrasound imaging may have good applicability in both high-altitude pulmonary edema (HAPE) and high-altitude cerebral edema (HACE). Pulmonary edema (or fluid in the lungs) is identified as “B-lines” or “comet tails” and is easily distinguishable on ultrasound (Gargani, 2019).

Using ultrasound to measure the diameter of the optic nerve can also assist with a diagnosis of HACE, as an increased diameter indicates increased intercranial pressure from HACE (Shookahi et al., 2020). The advantages of ultrasound over traditional imaging include being highly portable and usable in austere environments (such as back country), no radiation like many other imaging techniques, accurate for diagnosing pulmonary edema and other conditions, and takes little time for providers to master. Ultrasound also has a significant cost savings as the machine itself is relatively inexpensive, does not require special construction like adding lead to an Xray room, and is applicable in many other diagnoses (including kidney disorders, gallbladder disease, pneumonia, trauma, muscular disorders, and gynecological complaints). Ultrasound also has the capability to differentiate types of pulmonary edema, as well as other lung disorders, and generally much faster than a traditional Xray as there is no radiographic lag between clinical onset and ultrasound changes.

Pulmonary Edema on Xray Mayo Clinic, 2024

In HAPE, an increase in the number of B-lines indicates an accumulation of fluid in the lungs. Healthy individuals acclimating to the altitude have been shown to have a physiologic increase in B-lines during the first 4 days of high-altitude exposure as well as pregnant individuals having an increase in their baseline b-line count. Keeping these differences in mind, an increase of B-lines of more than 3 in a lung field, in more than 2 lung fields indicates an increase in extravascular lung water (EVLW) and could support a diagnosis of HAPE. Correlating this with clinical signs and symptoms of altitude sickness (HA, dizziness, fatigue, shortness of breath, nausea/vomiting), as well as HAPE (hypoxia, cough, exercise intolerance) can support a more rapid diagnosis of HAPE as well as assist with deciding need for oxygen and/or altitude descent (Yang et al., 2018; Heldeweg et al., 2022). The provider can also use the ultrasound to monitor resolution of the pulmonary edema to help support decisions to discontinue oxygen or to encourage altitude descent. Those with comorbidities such as heart failure can also be monitored for early signs that their treatment plan is not adequately addressing their EVLW and can receive correction prior to needing hospitalization (Chiu et al., 2022).

HACE, as a disorder including altered mental status, ataxia, headache, loss of consciousness, and seizures, is a serious complication of high altitude. As the symptoms suggest, rapid identification is key to reducing other problems, including death, from HACE. The use of ultrasound is relatively new in assisting with diagnosis, but an increase in optic nerve diameter on ultrasound above 5 millimeters indicates that there is a good chance of brain swelling (or cerebral edema) and subsequent increased intracranial pressure. Identifying this early allows for rapid decision making the descent to a lower altitude or using a more rapid evacuation method (helicopter or rapid ground transport). Increased intracranial pressure can also result from head injury or trauma and thus can be useful in settings where an injury may have occurred. This makes this a tool that could be invaluable in search and rescue operations or for first responders (Shookahi et al., 2020).

Keeping these benefits in mind, remember that diagnostic imaging is a support tool and not the complete answer to all health problems. Hopefully soon we will see this tool being used with more frequency to help aid our healthcare providers in determining a more accurate cause of symptoms!

References

Chiu, L., Jairam, M. P., Chow, R., Chiu, N., Shen, M., Alhassan, A., Lo, C.-H., Chen, A., Kennel, P. J., Poterucha, T. J., & Topkara, V. K. (2022). Meta-Analysis of Point-of-Care Lung Ultrasonography Versus Chest Radiography in Adults With Symptoms of Acute Decompensated Heart Failure. The American Journal of Cardiology, 174, 89–95. https://doi.org/10.1016/j.amjcard.2022.03.022

Gargani L. (2019). Ultrasound of the Lungs: More than a Room with a View. Heart Failure Clinics, 15(2), 297–303. https://doi.org/10.1016/j.hfc.2018.12.010

Heldeweg, M. L. A., Smit, M. R., Kramer-Elliott, S. R., Haaksma, M. E., Smit, J. M., Hagens, L. A., Heijnen, N. F. L., Jonkman, A. H., Paulus, F., Schultz, M. J., Girbes, A. R. J., Heunks, L. M. A., Bos, L. D. J., & Tuinman, P. R.. (2022). Lung Ultrasound Signs to Diagnose and Discriminate Interstitial Syndromes in ICU Patients: A Diagnostic Accuracy Study in Two Cohorts*. Critical Care Medicine, 50(11), 1607–1617. https://doi.org/10.1097/ccm.0000000000005620

Mayo Clinic (2024). Pulmonary Edema. Mayo Foundation for Medical Education and Research. Retrieved February 27, 2024 from https://www.mayoclinic.org/diseases-conditions/pulmonary- edema/symptoms-causes/syc-20377009

Shokoohi, H., Pyle, M., Kuhl, E., Loesche, M. A., Goyal, A., LeSaux, M. A., Boniface, K. S., & Taheri, M. R. (2020). Optic Nerve Sheath Diameter Measured by Point-of-Care Ultrasound and MRI. Journal of neuroimaging : official journal of the American Society of Neuroimaging, 30(6), 793–799. https://doi.org/10.1111/jon.12764

Yang, W., Wang, Y., Qiu, Z., Huang, X., Lv, M., Liu, B., Yang, D., Yang, Z., & Xie, T.. (2018). Lung Ultrasound Is Accurate for the Diagnosis of High-Altitude Pulmonary Edema: A Prospective Study. Canadian Respiratory Journal, 2018, 1–9. https://doi.org/10.1155/2018/5804942