Evaluation of the Effect of Intravenous Mannitol and Hypertonic Saline on Intraocular Pressure and Biometry Parameters in Anesthetized Horses With Experimentally Increased Intracranial Pressure.

Abstract

OBJECTIVE: To evaluate the effect of intravenous mannitol and hypertonic saline (HS) on intraocular pressure (IOP) and biometry parameters of horses with elevated intracranial pressure (ICP). PROCEDURES: Seven horses with normal ophthalmic exams were anesthetized and placed in lateral recumbency. A subarachnoid transducer was placed, and the head was lowered until ICP measured 40&#x2009;mmHg +/- 2&#x2009;mmHg. Five intravenous boluses of mannitol 20% (0.4&#x2009;g/kg) or HS 7.2% (1&#x2009;mL/kg) were administered, each 15&#x2009;min apart. A 2-day washout period ensued, and the procedure was repeated with the other hyperosmotic agent. IOP via a TonoVet, axial length and vitreous chamber depth via biometry, and ICP via the subarachnoid transducer were monitored. RESULTS: No significant correlation between ICP and IOP was identified. Estimated marginal mean (EMM) reduction in IOP (comparing values 5&#x2009;min post bolus to values at bolus administration) following mannitol and HS was 2.4&#x2009;mmHg and 0.4&#x2009;mmHg, respectively. Mean axial length EMM decreased by and increased by 0.1&#x2009;mm following mannitol and HS, respectively. Mean vitreous chamber depth EMM was unchanged and increased by 0.1&#x2009;mm following mannitol and HS, respectively. The EMM of the second HS bolus demonstrated an increase of 0.8&#x2009;mm (95% confidence interval 0.01-1.5&#x2009;mm) in axial length (p&#x2009;<&#x2009;0.048), though the remaining individual bolus assessments were not statistically significant. CONCLUSIONS: Intravenous mannitol and HS did not cause a significant change in IOP, axial length, or vitreous chamber depth in healthy, anesthetized, laterally recumbent horses in this experimental model of increased ICP.