Using Optic Nerve Sheath Diameter to Monitor Intracranial Tension in Pre-Eclamptic Parturient Receiving Magnesium Sulfate in Combination With Dexmedetomidine

Dexmedetomidine, a highly selective α-2-receptor agonist, is a first-line sedative medication in ICU and has been increasingly used for obstetric anesthesia. Dexmedetomidine, which provides light sedation, possesses analgesic, sympatholytic, anxiolytic properties and attenuates the stress response without significant respiratory depression. In addition, dexmedetomidine-induced stimulation of postsynaptic alpha-2 adrenergic receptor on the cerebral blood vessels can cause cerebral vasoconstriction and decrease cerebral blood flow. However, the effects of dexmedetomidine on ICP are controversial.

Clinical signs of raised ICP are not specific and often difficult to interpret, especially during pregnancy and pre-eclampsia. Though the use of invasive devices is considered a gold standard in the measurement of ICP, Ocular sonography is a promising bedside tool, which serves as a noninvasive, readily available, and cost-effective means for indirectly measuring ICP.

Bedside ultrasound can be used as a point-of-care tool for rapidly measuring the optic nerve sheath diameter (ONSD), which is a validated indirect means for measuring ICP. An increase in ICP reflects as a raised ONSD since the optic nerve is surrounded by Dural sheath and cerebrospinal fluid (CSF) containing subarachnoid space, which is distensible in the retrobulbar segment, particularly when CSF pressures rise.