Study Findings on ONSD Utility
A prospective observational study conducted at Indraprastha Apollo Hospitals in New Delhi has concluded that serial ultrasonographic measurements of the optic nerve sheath diameter (ONSD) are not reliable predictors of clinical outcomes in patients with sepsis-associated encephalopathy (SAE). The study, which followed 80 patients from May 2021 to October 2022, found no statistically significant correlation between ONSD measurements and Glasgow Coma Scale (GCS) scores, disease-severity markers, or length-of-stay outcomes.
While ONSD is frequently utilized as a non-invasive surrogate for intracranial pressure (ICP) in traumatic brain injury, its applicability in non-traumatic conditions like SAE remains controversial. Researchers measured bilateral ONSD at baseline (0 hours), 24 hours, 72 hours, on the fifth day, and during instances of clinical deterioration. Despite the rigorous measurement protocol, the data indicated that fluctuations in ONSD did not mirror the neurological decline or improvement observed in the patients.
Clinical Implications and Limitations
The study observed a statistically significant difference in baseline ONSD between non-survivors (5.35 ± 0.19 mm) and survivors (5.20 ± 0.23 mm) (p=0.035). However, when researchers applied a standard clinical threshold of 5.5 mm to categorize patients, the difference in mortality rates between those with elevated and normal ONSD was not statistically significant (30.0% versus 12.9%; p=0.16). This discrepancy suggests that while baseline measurements might hint at underlying severity, the ONSD is currently insufficient as a solitary prognostic tool.
The authors noted that the pathophysiology of SAE is multifactorial, involving neuroinflammation, endothelial dysfunction, and blood-brain barrier disruption, rather than simple intracranial hypertension. Consequently, relying on ONSD to monitor neurological status in these patients may overlook the complex systemic nature of the condition. The researchers emphasized that the 5.5-mm threshold finding should be treated as exploratory and cautioned against using it to guide clinical decision-making without further validation.
Future Research Requirements
The study underscores the necessity for larger, multi-center trials to establish whether standardized ONSD protocols can ever be integrated into the management of SAE. Current clinical practice continues to rely on traditional severity scores, such as the APACHE II and SOFA scores, to assess patient prognosis. As point-of-care ultrasound becomes more prevalent in intensive care settings, the research highlights a critical gap: the need for evidence-based thresholds that are specific to the non-traumatic encephalopathy population.