Association between intraoperative hypotension and motor evoked potential change in ossification of posterior longitudinal ligament and/or ossification of ligamentum flavum surgery.

Background: Intraoperative hypotension (IOH) is a recognized contributor to changes in motor evoked potential (MEP) during spinal surgeries. Additionally, it is essential to precisely define IOH across different surgical phases. However, there is limited data on optimal IOH thresholds for predicting MEP changes in thoracic ossification of the posterior longitudinal ligament (OPLL) and/or ossification of the ligamentum flavum (OLF) surgery. We aim to determine the IOH thresholds for predicting MEP changes during surgical treatment for OPLL and/or OLF based on different surgical phase. Methods: Data collected included demographic information, surgical details, mean arterial pressure (MAP) values, and MEP signals. A receiver operating characteristic (ROC) curve was employed to determine the MAP thresholds. A comparative analysis was performed to evaluate IOH episodes occurring during predecompression versus postdecompression surgical phases, specifically in the early and later stages. Additionally, a multivariate logistic regression analysis was conducted to assess the association between surgical variables and MEP change. Results: The MAP thresholds for predicting changes in MEP at the early surgical stage were determined as follows: 70 mmHg for patients with combined OPLL and OLF, 66 mmHg for OPLL patients, and 65 mmHg for OLF patients. However, it is recommended that MAP at the later surgical stage should be elevated to exceed 75 mmHg, 73 mmHg, and 71 mmHg in patients diagnosed with combined OPLL and OLF, OPLL, and OLF, respectively. A stronger correlation was observed between MAP variability ratio and MEP amplitude reduction ratio (ARR) during postdecompression surgical phase. At the early surgical stage, the administration of ephedrine bolus was identified as a risk factor for predicting MEP change (odds ratio [OR]=1.13, p<.01). At the later stage, the risk-factors included ephedrine bolus (OR=1.09, p<.01), estimated blood loss (per 100 mL) (OR=1.23, p=.02), and patients with combined OPLL and OLF (OR=12.12, p<.01). Conclusions: We determined cutoff values for MAP to predict changes in MEP in patients undergoing surgical treatment for OPLL and/or OLF based on different surgical phases. Compared to the early surgical stage, patients exhibit less tolerance to IOH at the later surgical stage. A stronger correlation was observed between the MAP variability ratio and MEP ARR at the later surgical stage. Additionally, we identified surgical factors that are associated with a higher probability of MEP change.