COMPARISON OF ULTRASONOGRAPHIC OPTIC NERVE SHEATH DIAMETER BEFORE AND AFTER MANNITOL ADMINISTRATION IN DOGS WITH PRESUMED INTRACRANIAL HYPERTENSION

Carlos Valerio-López

doi:10.7273/000007098

Intracranial hypertension (ICH) is a life-threatening condition commonly seen in human and veterinary patients suffering from intracranial diseases of various etiologies. Treatment involves hyperosmolar therapy to lower intracranial pressure (ICP). Identification of ICH can be challenging since the gold standard involves placement of invasive intracranial pressure monitoring systems or advanced imaging techniques requiring anesthesia, which may be contraindicated in these patients. Moreover, clinical signs associated with ICH are often seen only with impending brain herniation, leaving little time for intervention. This poses a pressing need for novel biomarkers of ICH that are quick, reliable, safe, non-invasive, cost-effective, and accurate, to identify ICH and monitor patients. Optic nerve sheath diameter measured by ultrasound (ONSD-US) has been proposed as one such tool. However, it has not been systematically studied whether ONSD-US is a dynamic, bi-modal biomarker that changes with hyperosmolar therapy. This prospective observational study was designed to evaluate the utility of ultrasonographic ONSD-US as a dynamic biomarker of ICH following administration of mannitol in patients with clinically suspected ICH. We hypothesized that ONSD-US in dogs with clinically suspected ICH would decrease following hyperosmolar therapy. Patient recruitment and evaluation was done over 1 year, at a University Teaching Hospital. Patients were followed for up to 60 minutes beyond treatment. Ten prospectively recruited client-owned dogs with clinically suspected ICH (consecutive sample) and weight-matched to ten healthy control dogs were recruited for this study. Bilateral transpalpebral ONSD-US images were collected using a handheld ultrasound probe in dogs with clinically suspected ICH before (t0) and at 30 (t30) and 60 (t60) minutes after administration of mannitol therapy (1g/kg IV). Measurements were collected and then evaluated by 3 observers and compared for agreement. At each time point, clinical examination was performed, vital parameters recorded, and neurological scores were assigned using the Modified Glasgow Coma Scale, Neurological Deficit Score and Animal Functional Capacity tools. Bilateral baseline ONSD-US measurements were also collected from weight-matched control dogs using the same technique. Control dogs had a lower mean (+/- SD) ONSD-US (1.6 +/- 0.4mm) than dogs with suspected ICH at baseline (2.0 +/- 0.6mm; P= 0.006). Amongst dogs with suspected ICH, ONSD-US was decreased from baseline (2.0 +/- 0.6mm) at t30 (1.8 +/- 0.6mm; P=0.005) and t60 (1.7 +/- 0.5mm; P=0.003). There was no significant difference between t30 and t60 (P=0.17). Inter rater and intra rater reliability was excellent (ICC >0.90). The modified Glasgow Coma Scale and Neurological Deficit Score showed significant changes over time (P=0.02 and P=0.04 respectively) while Animal Functional Capacity scores were not significantly different. Our results indicate that the ONSD-US decreases over time in response to hyperosmolar therapy and may be a useful non-invasive, dynamic biomarker to identify and monitor ICH and response to therapy.

COMPARISON OF ULTRASONOGRAPHIC OPTIC NERVE SHEATH DIAMETER BEFORE AND AFTER MANNITOL ADMINISTRATION IN DOGS WITH PRESUMED INTRACRANIAL HYPERTENSION

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