Comparison of Ultrasonographic Optic Nerve Sheath Diameter Before and After Mannitol Administration in Dogs with Presumed Intracranial Hypertension

ABSTRACT Objective To evaluate ultrasonographic optic nerve sheath diameter (ONSD‐US) as a dynamic biomarker of intracranial hypertension (ICH) following administration of mannitol in patients with clinically suspected ICH. Design Prospective observational study over 1 year. Patients were followed for 60 min beyond treatment. Setting University teaching hospital. Animals Ten prospectively recruited client‐owned dogs with clinically suspected ICH (consecutive sample) and 10 weight‐matched, healthy control dogs. Interventions Bilateral transpalpebral ONSD‐US images were collected using a handheld ultrasound probe in dogs with clinically suspected ICH before ( t 0 ) and at 30 min ( t 30 ) and 60 min ( t 60 ) after administration of mannitol therapy (1 g/kg IV). Measurements were collected and evaluated by three observers and compared for agreement. At each time point, a clinical examination was performed, vital parameters were recorded, and neurological scores were assigned using the Modified Glasgow Coma Scale, the Neurological Deficit Score, and the Animal Functional Capacity tools. Bilateral baseline ONSD‐US measurements were also collected from weight‐matched control dogs using the same technique. Measurements and Main Results Control dogs had a lower mean (± SD) ONSD‐US (1.6 ± 0.4 mm) than dogs with suspected ICH at baseline (2.0 ± 0.6 mm; p = 0.006) on a paired t ‐test. Among dogs with suspected ICH, compared using a one‐way ANOVA with Tukey's multiple comparisons test, ONSD‐US was decreased from baseline (2.0 ± 0.6 mm) at t 30 (1.8 ± 0.6 mm; p = 0.005) and t 60 (1.7 ± 0.5 mm; p = 0.003). There was no difference between t 30 and t 60 ( p = 0.17). Interrater and intrarater reliability were excellent (ICC >0.90). Physiological parameters and neurological scores did not change among the time points assessed, while the Neurological Deficit Score decreased over time ( p = 0.04; R 2 = 0.51). Conclusions ONSD‐US decreases over time with hyperosmolar therapy and may be a useful noninvasive, dynamic biomarker to identify and monitor ICH and response to therapy.