Medical Student Tufts University School of Medicine Boston, Massachusetts, United States
Introduction: Spinal anesthesia (SA) has recently shown applicability and benefit in spinal surgery. However, if the initial dose provides inadequate analgesia, an additional dose or conversion to general endotracheal anesthesia may be required, both of which are disruptive to the surgical workflow.
Methods: We reviewed cases of lumbar surgery performed under spinal anesthesia from 2017 – 2022. We identified 13 cases of inadequate first dose of spinal anesthesia, then selected 39 random patients as controls. We measured the cross-sectional area of the dural sac using T2-weighted MRI sequences and used a measurement tool to approximate the area for each patient.
Results: Patients who had an inadequate first dose of anesthesia had a significantly larger dural sac cross-sectional area at the level of anesthetic injection, 183.0 ± 61.9 mm2 in the inadequate dose group, and 136.1 ± 42.0 mm2 in controls (p=0.015). The inadequate dose group was significantly younger, 55.8 ± 10.4 years in failed first dose, and 66.4 ± 11.0 years in control (p=0.002). The groups did not differ by surgical procedure (p=0.165), level (p=0.394), ASA score (p=0.812), or co-morbidities.
Conclusion : We found that age and dural sac cross-sectional area are both risk factors for an inadequate first dose of spinal anesthesia. The availability of spinal MRI in patients undergoing spine surgery allows the identification of patients with a large lumbar cistern. This data may be used for dose-adjusted anesthesia based on anatomic variables.
