Objective: To determine if ultrasound guided measurement of the optic nerve sheath diameter accurately predicted elevated intracranial pressure (ICP) as demonstrated by cranial computed tomography (CT) in at-risk emergency department patients.
Methods: Optic nerve sheath diameters were measured on a convenience sample of adult patients presenting with suspected elevated ICP to the emergency department of a large teaching hospital over a 6-month period. A cut off for optic nerve sheath diameter of 5 mm was considered positive for elevated ICP. All patients had a subsequent cranial CT scan on the same day reported by a radiologist. Signs of elevated ICP on cranial CT include midline shift with a mass effect of at least 3 mm, sulcal effacement with evidence of significant oedema, collapse of ventricles, and cisternal compression.
Results: Twenty-four patients were recruited with a sensitivity of 100% [95% confidence interval (CI), 83.8-100] and specificity of 75% (95% CI, 30.1-95.4) with a cut-off of 5 mm for optic nerve sheath diameter to predict elevated ICP on cranial CT scan. The positive predictive value for an increased optic nerve sheath diameter for elevated ICP was 95.4% (95% CI, 74.13-99.75) and negative predictive value was 100% (95% CI, 31-100). The positive likelihood ratio of a wide optic nerve sheath diameter for elevated ICP on cranial CT was calculated to be 4.00 (95% CI, 0.73-21.84).
Conclusion: This study shows that the ultrasound guided optic nerve sheath diameter is a sensitive and specific test for predicting elevated ICP. A prospective validation study across emergency departments would test applicability of this test. We propose an algorithm for incorporating ultrasound for the management of suspected intracranial hypertension in emergency departments.