In vivo glycocalyx assessment in aneurysmal subarachnoid hemorrhage patients: protocol for a prospective observational feasibility study

BackgroundDelayed cerebral ischemia (DCI) following aneurysmal subarachnoid hemorrhage (aSAH) is a severe complication linked to prolonged hospitalization, reduced functional outcomes, and increased mortality. Due to a lack of validated biomarkers, its development remains unpredictable, and its management is challenging. The glycocalyx, a glycoprotein layer on the luminal surface of endothelial cells, plays a crucial role in regulating leukocyte adhesion, thrombosis, and vascular permeability. As DCI is thought to result from microthrombosis, inflammation, and oxidative stress, the glycocalyx may be a relevant biomarker for DCI. This study aims to determine the feasibility of in vivo glycocalyx measurements in aSAH patients and to determine how these markers change over time in relation to DCI.MethodsThis prospective observational feasibility study will involve 30 aSAH patients. Glycocalyx thickness will be visualized in vivo using sidestream darkfield (SDF) imaging both sublingually and on the conjunctiva, while glycocalyx breakdown will be quantified ex vivo in blood samples. Measurements will be repeated six times during the first 2-week post-ictus. The primary outcome will be the feasibility of the in vivo glycocalyx measurements assessed as a multidimensional outcome, including technical feasibility, operational feasibility, participant experience, and measurement safety. Mixed model analysis will compare the feasibility of sublingual and conjunctival measurements including variables such as age, sex, neurological status, and patient location during measurement. Secondary outcomes will be the responsiveness of the in vivo glycocalyx measurements to DCI, compared to ex vivo glycocalyx measurements, analyzed using mixed-effects logistic regression.DiscussionTraditionally, the search for DCI biomarkers has focused on systemic measurements of cerebrovascular breakdown products, which may vary due to metabolism and renal or hepatic clearance. In vivo assessment of the glycocalyx by SDF imaging is a minimally invasive method that allows for direct, local, and dynamic evaluation of the microcirculation. Given that the conjunctiva is vascularized by the ophthalmic artery branching off the internal carotid artery, it may better reflect cerebral microvascular changes associated with DCI. If feasible, in vivo glycocalyx measurements could serve as a valuable biomarker for monitoring DCI in aSAH patients, potentially offering superior predictive value compared to systemic measurements of glycocalyx breakdown products.