Real-time Reduction in Optic Nerve Sheath Diameter Following Hypertonic Saline Bolus in a Patient with Penetrating Traumatic Brain Injury: A Case Report

The Joint Trauma System Clinical Practice Guideline on Traumatic Brain Injury Management in Prolonged Field Care recommends the use of ultrasound measurement of optic nerve sheath diameter (ONSD) in the neurologic assessment of unconscious patients without ocular injury. This recommendation is well-founded in the literature, and support is growing for use of ONSD measurement for monitoring of neurocritical patients, especially in resource-limited and austere environments, including military theaters of operation. Our patient presented as a level 1 trauma patient with a penetrating traumatic brain injury (TBI). ONSD measurements taken before, during, and after administration of a 250mL bolus of 3% hypertonic saline showed a downward trend in ONSD measurement, from 5.4 to 4.8mm in the right eye, and 7.6 to 6.3mm in the left eye, within 20 minutes. Our review of the literature identified studies in which ONSD decreased following treatment of symptomatic hyponatremia with 3% hypertonic saline, as well as cases in which ONSD decreased in real time following lumbar puncture and external ventricular drain placement. Many studies also demonstrate the usefulness of ONSD for screening and monitoring of patients with TBI. Ours is the first reported instance of which we are aware showing real-time reduction in ONSD following treatment with 3% hypertonic saline in a patient with a penetrating TBI. ONSD measurement has potential for neurocritical monitoring in austere, resource-limited environments, including prolonged field care. Further study is needed to interrogate the accuracy and reliability of ONSD measurement as a tool for assessing treatment efficacy in patients with TBI, both blunt and penetrating.