Waveform analysis for lumbar epidural needle placement in labour

Epidural analgesia is highly effective for labour pain relief, but can be challenging to perform in labouring patients 1. The ability to transduce a pulsatile pressure waveform from epidural needles in non-pregnant patients correlates with successful epidural blockade 2-7. We have evaluated the feasibility of transducing an epidural waveform in labouring women. With ethics board approval and written informed consent, we studied ten term labouring patients requesting epidural labour analgesia, prospectively. After epidural needle placement at the L3-4 interspace using a loss-of-resistance to saline technique, a standard pressure monitoring system (TruWaveTM Pressure Monitoring Set; Edwards Lifesciences LLC, Irvine, CA, USA) was connected to the 17G Tuohy needle (CHS®, Oakville, ON, Canada) and then to a standard 20G polyurethane epidural catheter (Portex®, Smiths Medical ASD Inc., Keene, NH, USA) during and between contractions. Pressure values were recorded via 10-s videos taken from a portable monitor and analysed offline by a blinded investigator. A test dose (3 ml of lidocaine 2% with adrenaline 1:200,000) and epidural top-up (10 ml of bupivacaine 0.125%) were administered. Thirty minutes later, all patients had an adequate bilateral block, confirming that the epidural catheter was correctly positioned. No epidural pressure waveforms were observed in our study. Compared to non-pregnant participants in previous (thoracic) epidural pressure waveform studies, we attribute our findings to anatomical and physiological differences in the lumbar epidural space of parturients, with weaker arterial pulsation 8, increased tissue compliance 9 and increased epidural pressures 10. We conclude from our small pilot study that lumbar epidural pressure waveform analysis is not feasible in parturients.