Optic Nerve Sheath Diameter for Volume Status Prediction in Severe Preeclampsia

Overview

A quick, non-invasive, bedside test to assess fluid status of patients with severe preeclampsia would be very helpful to ICU clinicians severe preeclampsia is associated with an increase in extravascular lung water (EVLW), which can be identified by lung ultrasound before appearance of clinical signs of pulmonary edema but this technique still requires several measurements and could be time consuming. Optic ultrasound is also a safe and repeatable diagnostic tool, which is even quicker and simpler to perform than lung ultrasound. Increased ONSD is associated with increased ICP and it can indirectly reflect the state of intracranial edema that could be a part of generalized edema. More data on the correlation between ONSD and markers of fluid status (EVLW by ultrasound) are needed before ONSD measurements can be recommended as a guide to fluid management in preeclampsia.

Severe preeclampsia (PE) is a progressive multisystem pregnancy disorder. It is considered the second leading cause of maternal death worldwide. Usually, it is diagnosed by the new-onset hypertension and either proteinuria or end-organ dysfunction in the second half of pregnancy. Acute Pulmonary edema is potentially lethal and is the most common cardiopulmonary complication of preeclampsia. thus, meticulous fluid management of these patients is crucial but it is often difficult because the underlying endothelial damage leads to water, electrolytes, and plasma leakage from the intravascular space which produce significant fluid shifts into the interstitial space resulting in peripheral and/or central (pulmonary and central nervous system) edema. Also, there is a potential for hypovolemia due to the depletion of intravascular volume. Under-resuscitation of preeclampsia patients impairs organ perfusion; while on the other hand fluid overload leads to tissue edema and aggravates pulmonary edema. Therefore, fluid administration must be assessed to preserve organ perfusion, while preventing lung congestion and pulmonary edema. Early detection of lung congestion would allow early and optimal management of these patients. Lung ultrasound was reported as a useful diagnostic tool which could identify increased levels of extravascular lung water (EVLW) in severe PE before clinical signs of pulmonary edema appear. Consequently, lung ultrasound could guide fluid management and identify those in need for diuretic therapy among severe PE patients. Though it is considered accurate, safe, and non-invasive valuable tool, its use could be limited by the need to several measurements that could be time consuming. Changes in the Optic Nerve Sheath Diameter (ONSD) detected by ultrasound are considered an important clinical and radiographic demonstration of increased intracranial pressure (ICP) which is one of the consequences of preeclampsia. Therefore, Increased ONSD can indirectly reflect the state of intracranial edema that could be a part of generalized edema. On ultrasound the ONSD is measured 3 mm posterior to the globe for both eyes. A position of 3 mm behind the globe is recommended because the ultrasound contrast is greatest; the results are more reproducible and the normal optic nerve sheath measures up to 5.0 mm in diameter. An average ONSD greater than 5 mm is considered abnormal and elevated intracranial pressure should be suspected. Chen et al., studied ONSD and the intravascular volume status of patients after cardiac surgery and found that changes in ONSD can dynamically reflect changes in volume status in patients with postoperative cardiac surgery.