To evaluate and correlate the effectiveness of epidural depth equation versus pre-procedural US guided epidural block: A randomized controlled trial

Ultrasound assisted pre-procedural epidural depth estimation has improved the safety and efficacy of epidural block. Currently, the incorporation of pre-procedural ultrasound guided epidural derived equation(EDE) has significantly improved the accuracy of epidural depth estimation especially in the parturients. However, the accuracy of EDE derived epidural depth alone has not been compared to the actual epidural needle depth in non-obstetric patients. This study compared the efficacy of epidural depth equation (EDE) versus pre-procedural US-guided epidural block in patients scheduled for orthopedic surgeries under the combined spinal epidural block (CSE). The primary outcome was the number of attempts for successful epidural insertion, the secondary outcomes were correlations of EDE-calculated epidural depth with actual needle depth and pre-procedural US-guided epidural depth. One hundred patients, 20-60 years, ASA physical status I and II, body mass index (BMI) 18.5–29.9 kg.m were randomized into two groups. In group US (n=50), the pre-procedural US-guided skin to epidural depth was measured and the point of insertion of the epidural needle was marked. Whereas, in group E (n=50), the skin epidural depth was measured using the epidural depth equation (EDE). The epidural block was instituted by the loss of resistance technique in both groups. The primary outcome was the number of attempts for successful epidural insertion, the secondary outcomes were correlations of EDE-calculated epidural depth with actual needle depth and pre-procedural US-guided epidural depth. The needle passes were 1.10±0.08, and 1.18±0.05 in groups US, E respectively (P=0.251). A significantly strong correlation was observed between epidural depth by US and EDE (r2=0.915, P=0.001). Whereas, a weak correlation was observed in the EDE-measured epidural depth and actual needle depth (r=0.402, P =0.04). Although comparable needle attempts were observed in both groups, the weak correlation of epidural depth by EDE with actual needle depth doesn’t support its use alone. The strong correlation of epidural depths by EDE and US encourages EDE assisted with pre-procedural US-guided epidural block.