Ultrasound assisted exploration of the primary anatomical dimension of lumbar epidural fat affecting epidural labour analgesia

Abstract

Abstract Background There is ambivalence about the effect of epidural fat on local anaesthetic diffusion in epidural anaesthesia. This study aimed to investigate the primary anatomical dimension of epidural fat affecting epidural labour analgesia using ultrasound measurements of the ligamentum flavum-dura mater unit (LFDM). Methods A total of 162 women who received epidural labour analgesia were included in this study. The height (H), diameter (d), and volume (V) of the lumbar LFDM were measured and calculated using ultrasound as a proxy for the dimensions of epidural fat. After anaesthesia, the main observations were whether the analgesia was effective within 30 min and the changes in the levels of temperature and pain blockade within 30 min. Results A total of 160 patients completed the follow-up. The height (H) of the LFDM (AUC = 0.882) was more predictive of maternal analgesia than the volume (V) of the LFDM (AUC = 0.667). Although the volume (V) of the LFDM was weakly correlated with the temperature block level (r=-0.423, P < 0.0001) and pain block level (r=-0.459, P < 0.0001), the height (H) of the LFDM was strongly correlated with the temperature block level (r=-0.864, P < 0.0001) and pain block level (r=-0.811, P < 0.0001). With a height (H) of LFDM = 12.06 as the cutoff, the sensory block level was significantly higher in the short LFDM group than in the long LFDM group within 30 min. Conclusion The height (H) of the lumbar LFDM, as determined by ultrasound, rather than its volume, is the primary anatomical dimension of epidural fat that affects epidural labour analgesia.