Optic Nerve Sheath Diameter in Hyponatremia: A Closer Look

Jes Jose¹https://orcid.org/0000-0003-1734-9519, Varun Suresh²https://orcid.org/0000-0003-2521-1149, Rohan Magoon³https://orcid.org/0000-0003-4633-8851

¹Department of Cardiac Anesthesiology, Sri Jayadeva Institute of Cardiovascular Sciences and Research, Bengaluru, Karnataka, India

²Deparetment of Anesthesia and Intensive Care, Jaber Al Ahmad Al Sabah Hospital, Kuwait-Arabian Gulf

³Department of Anaesthesia, Atal Bihari Vajpayee Institute of Medical Sciences (ABVIMS) and Dr. Ram Manohar Lohia Hospital, New Delhi, India

Corresponding Author: Varun Suresh, Department of Anesthesia and Intensive Care, Jaber Al Ahmad Al Sabah Hospital, Kuwait-Arabian Gulf, Phone: +9041426743, e-mail: varunsureshpgi@gmail.com

How to cite this article: Jose J, Suresh V, Magoon R. Optic Nerve Sheath Diameter in Hyponatremia: A Closer Look. Indian J Crit Care Med 2023;27(6):452.

Source of support: Nil

Conflict of interest: None

Keywords: Hyponatremia, Optic nerve sheath diameter, Ultrasonography.

Dear Editor,

The research study by Uttanganakam et al.¹ brings to light a significant decrease in optic nerve sheath diameter (ONSD) after treatment of hyponatremia compared to pretreatment levels (mean right eye ONSD = 5.81 ± 0.58 mm [95% confidence interval (CI): 0.27–0.59, p < 0.001], and left eye ONSD = 5.79 ± 0.56 mm [95% CI: 0.29–0.64, p < 0.001] after hyponatremia correction; compared to mean right eye ONSD = 6.24 ± 0.71 mm and left eye ONSD = 6.26 ± 0.64 mm at presentation to the emergency department). However, the ONSD measurements failed to predict moderate to severe hyponatremia on receiver operating characteristic curve (ROC) analysis in the index prospective cohort. The author’s attempt to extend the point of care utility of ultrasonographic measured ONSD to the emergency department deserves applause, though herewith we appraise a few facets to consider while extrapolating sub-millimetric variations in ONSD to clinical outcome.²

Uttanganakam et al. measured ONSD in the transverse plane with a high-frequency linear ultrasound probe using B-mode with the patient eyes closed, using hypoechoic lines behind the eye globe as reference. In B-scan, the ultrasonographic waves reach the optic nerve in a non-perpendicular array and hence measurements are predisposed to “scattering” and “blooming effect” artifact.³ Despite the use of an ophthalmic setting Uttanganakam et al. contemplated, ONS wall brightness varies with ‘gain’ adjustments in B-scan. That said the index measurement being ONSD, variations in microns can affect the accuracy and precision of readings.⁴ Therefore, we suggest that A-scan ultrasound (wherein the ONS is easily noticeable as hyperreflective spikes), be used especially so in the emergency department cohort of patients as time constraints and quicker decision-making are pertinent here.

That, 44.4% of cases in the index cohort had vomiting leaves the readers intrigued by the extent to which dehydration could have influenced ONSD measurements in hypovolemic hyponatremia. It is appreciated that the authors have carefully excluded hypervolemic hyponatremia, yet hypovolemia can alter cerebrospinal fluid production and dynamics consequently affecting ONSD measurements. Though Uttanganakam et al. ‘practiced’ ONSD imaging in 80 individual measurements prior to the study to avoid interobserver variability in measurements, how the authors ‘blinded’ their investigators to the nature of the image procured (before and after sodium correction) has been left unaccounted. Further, we appreciate that Uttanganakam  et al. has carefully excluded head injury patients from their research wherein septations and ONS compartmentalization can mandate separate correlation of right and left ONSD measurements to the studied outcome, nevertheless, we believe that the average of either side ONSD can be better representative in the correlation and ROC analysis of the Uttanganakam et al. hyponatremia cohort of cases.⁵

ORCID

Jes Jose https://orcid.org/0000-0003-1734-9519

Varun Suresh https://orcid.org/0000-0003-2521-1149

Rohan Magoon https://orcid.org/0000-0003-4633-8851

REFERENCES

1. Uttanganakam S, Hansda U, Sahoo S, Shaji IM, Guru S, Topno N, et al. Sonographic optic nerve sheath diameter as a guide for correction of hyponatremia in the emergency department: A cross-sectional study. Indian J Crit Care Med 2023;27(4):265–269. DOI: 10.5005/jp-journals-10071-24438.

2. Arunachala S. Optic nerve sheath diameter and sodium levels: A friend of a friend is still a stranger. Indian J Crit Care Med 2023;27(4):235–236. DOI: 10.5005/jp-journals-10071-24444.

3. Cornetta P, Marotta G, De Bernardo M, Vitiello L, Rosa N. Ultrasound and optic neuritis. Am J Emerg Med 2019;37(8):1598. DOI: 10.1016/j.ajem.2019.02.001.

4. Stevens RRF, Gommer ED, Aries MJH, Ertl M, Mess WH, Huberts W, et al. Optic nerve sheath diameter assessment by neurosonology: A review of methodologic discrepancies. J Neuroimaging 2021;31(5):814–825. DOI: 10.1111/jon.12906.

5. Suresh V, Sharma S, Aggarwal A. Correlation between ultrasonographic optic nerve sheath diameter and intracranial pressure in patients with aneurysmal subarachnoid hemorrhage. Neurocrit Care 2020;33(3):860–861. DOI: 10.1007/s12028-020-01087-y.

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