AbstractBackground and purposeHaving good collaterals is associated with better clinical outcomes in patients undergoing endovascular thrombectomy. This study aims to evaluate whether the effect of collateral status on functional outcomes is modified by volemia at admission.MethodsThis is a single‐center, retrospective analysis of patients who had acute proximal anterior circulation occlusion and underwent endovascular thrombectomy between January 2019 and June 2022. Volemia at admission, evaluated by blood urea nitrogen‐to‐creatinine ratio, was used to dichotomize patients into dehydrated and hydrated groups. The primary outcome was functional independence (90‐day modified Rankin Scale score = 0–2). Secondary outcomes were the rates of successful reperfusion, 24‐h symptomatic intracranial hemorrhage, and 90‐day all‐cause mortality. Multivariable logistic regression analysis was used to assess the interaction between collateral status and volemia at admission on outcomes.ResultsA total of 290 patients were enrolled, among whom having good collaterals was associated with functional independence (adjusted odds ratio [OR] = 2.71, 95% confidence interval [CI] = 1.41–5.22,p = 0.003). Having good collaterals benefited dehydrated patients (adjusted OR = 3.33, 95% CI = 1.45–7.63,p = 0.004) but not hydrated patients (adjusted OR = 2.21, 95% CI = 0.73–6.68,p = 0.161). However, an interaction between collaterals and volemia at admission on functional independence was not observed (p = 0.319). The rates of successful reperfusion, symptomatic intracerebral hemorrhage, and all‐cause mortality were similar between those with good and poor collaterals in both dehydrated and hydrated patients.ConclusionsThe effect of collateral status on the functional independence of patients undergoing thrombectomy is not modified by volemia at admission.