Preferential Flow Patterns of Injectate in Epidural and Inadvertent Subdural Anesthesia: Exploring the Hemodynamic Stability of High-Level Epidural, Subdural and Combined Epidural-Subdural Blocks in Relation to ASA Class.

Purpose: This study examines the hemodynamic responses elicited by epidural, subdural, and combined epidural-subdural anesthesia during spinal surgery, with a focus on anesthetic levels and ASA classifications. It integrates image findings to enhance understanding of the anesthetic impact on hemodynamic stability. Patients and Methods: A retrospective analysis was conducted involving patients who underwent endoscopic, open, or fusion spine surgeries with epidural anesthesia and monitored anesthesia care (MAC) between March 2018 and September 2023. Comprehensive demographic data, details regarding anesthetic levels, ASA class and hemodynamic measurements were systematically collected. Additionally, fluoroscopic images were assessed to investigate the distribution patterns of anesthetics and their relationship to hemodynamic outcomes. Results: In patients undergoing epidural, subdural, and combined epidural-subdural anesthesia with high-level blocks above T5 and classified as ASA class III or higher, no significant differences were observed in hypotensive events or vasopressor usage compared to those with lower-level blocks or ASA classifications. The mean duration of surgery was 90.6 ± 40.9, 105.4 ± 42.5, and 100.8 ± 46.6 minutes, respectively, across the three groups. Subdural anesthesia exhibited a similar hemodynamic profile, with milder blood pressure decreases. Imaging analysis indicated distinct anesthetic distribution patterns primarily in the posterior epidural and subdural spaces, which helped preserve anterior sympathetic and motor functions, suggesting a relationship between fluoroscopic imaging features and hemodynamic stability. Conclusion: Hemodynamic stability was maintained in the subdural and combined epidural-subdural groups compared to the epidural group in ASA I to III patients. However, epidural anesthesia showed better hemodynamic outcomes for ASA class above III. High-level epidural and subdural anesthesia primarily induced posterior diffusion, resulting in minimal anterior sympathetic block while preserving stability. These findings suggest that epidural anesthesia may be a viable alternative for spinal surgeries and applicable to other procedures for patients with high ASA classifications.