Anatomical dimensions of the lumbar dural sac predict the sensory block level of continuous epidural analgesia during labor

BACKGROUND: The anatomical dimensions of the lumbar dural sac determine the sensory block level of spinal anesthesia; however, whether they show the same predictive value during continuous epidural anesthesia (CEA) remains undetermined. We designed the present study to verify the efficacy of the anatomical dimensions of the lumbar dural sac in predicting the sensory block level during labor analgesia. METHODS: A total of 122 parturients with singleton pregnancies requesting labor analgesia were included in this study. The lumbar dural sac diameter (DSD), lumbar dural sac length (DSL), lumbar dural sac surface area (DSA), and lumbar dural sac volume (DSV) were measured with an ultrasound color Doppler diagnostic apparatus. CEA was performed at the L2-L3 interspace. After epidural cannulation, an electronic infusion pump containing 0.08% ropivacaine and sufentanil 0.4 μg/ml was connected. The sensory block level was determined with alcohol-soaked cotton, a cotton swab, and a pinprick. The analgesic efficacy of CEA was determined with a visual analog scale (VAS). The parturients were divided into two groups, “ideal analgesia” and “nonideal analgesia,” and the groups were compared by t test. Pearson’s correlation was performed to evaluate the association between the anatomical dimensions of the lumbar dural sac and sensory block level. Multiple linear regression analysis was used to create a model for predicting the sensory block level. RESULTS: In the ideal analgesia group, the height, DSL, DSA, DSV and DSD were significantly smaller, and the body mass index (BMI) was significantly larger (P < 0.05). In addition, the DSL demonstrated the strongest correlation with the peak level of pain block (r = − 0.816, P < 0.0001; Fig. 2A), temperature block (r = − 0.874, P < 0.0001; Fig. 3A) and tactile block (r = − 0.727, P < 0.0001; Fig. 4A). Finally, the multiple linear regression analysis revealed that DSL and BMI contributed to predicting the peak sensory block level. CONCLUSION: In conclusion, our study shows that the sensory block level of CEA is higher when the DSL, DSA, DSV and DSD of puerperae are lower. DSL and BMI can be treated as predictors of the peak sensory block level in CEA during labor analgesia. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s12871-021-01485-5.