Blood Urea Nitrogen and Atrial Fibrillation Identify Geriatric Peri-Hospitalization Cardiovascular and Cerebrovascular Vulnerability After Hip Arthroplasty

<title>Abstract</title> <p>Background Elderly patients undergoing hip arthroplasty carry high risks of in-hospital major adverse cardio-cerebrovascular events (MACCE), which prolong hospitalization and delay functional recovery. Conventional perioperative risk tools including the Revised Cardiac Risk Index (RCRI) lack targeted validation in elderly hip surgery populations, and readily available routine laboratory markers such as blood urea nitrogen (BUN) have not been fully incorporated into current perioperative risk assessment systems. This study aimed to identify key risk factors and develop a practical nomogram to provide preliminary evidence supporting orthopaedic perioperative risk evaluation. Methods Using MIMIC-IV version 3.1, we studied 1,253 patients aged 65 years or older who underwent hip arthroplasty and evaluated broad-definition in-hospital MACCE with strict-endpoint sensitivity analysis. Multivariable regression, repeated cross-validated risk stratification, BUN strata, accumulated core risk factors, and predefined descriptive subgroup analyses were used to characterize clinically interpretable risk signals. Results Broad MACCE occurred in 81 patients (6.46%), and strict MACCE occurred in 44 patients (3.51%). Older age, urgent or emergency admission, coronary artery disease, atrial fibrillation, and higher blood urea nitrogen (BUN) were independently associated with broad MACCE. BUN and atrial fibrillation showed the most consistent signals across primary, strict-endpoint, preprocedure-window, and descriptive subgroup analyses. MACCE risk increased stepwise with BUN level and with accumulation of core risk factors, reaching 24.8% among patients with BUN &gt; 30 mg/dL and 31.4% among patients with four or more core risk factors. Conclusions Elevated BUN and atrial fibrillation may help identify a geriatric renal-cardiovascular vulnerability profile among older adults undergoing hip arthroplasty and may support closer cardiovascular, renal-volume, rhythm, and geriatric co-management during hospitalization.</p>