A COMPARISON OF SENSORY AND MOTOR BLOCK OF A SINGLE BOLUS INJECTION OF 0.1% ROPIVACAINE AND 0.2% ROPIVACAINE IN LABOUR EPIDURAL ANALGESIA:

S256 INTRODUCTION: Ropivacaine is a relatively new local anaesthetic and the recommended concentration is 0.2%. We would like to determine if the 0.1% concentration could achieve similar degree of analgesia but with less motor block. We compared the sensory and motor block of a single bolus injection of similar dose but different concentration of ropivacaine (0.1% vs 0.2%) in labour epidural analgesia. METHODS: 30 primigravida parturients in active labour, with cervical dilatation 5 cm or less, were randomly assigned to receive a single bolus injection of either 20 ml 0.1% ropivacaine or 10 ml 0.2% ropivacaine. This was a prospective, randomised and double blinded study. Assessment of motor (Bromage), sensory (pinprick) and pain relief (VAS) were performed 20 min after the injection. If the Bromage score was zero, the parturients were assessed for straight leg raising weakness with a 4 point weakness scale(0=no weakness, 1=mild, 2=moderate, 3=severe). Additional top ups were administered if there was inadequate pain relief 20 min after the injection of the test drug. RESULTS: The pain scores, quality of analgesia and the height of sensory block between the two groups were not statistically significant. Although all parturients had Bromage score of 0, some degree of qualitative weakness (straight leg raising) could still be elicited in some parturients. 20% of parturients had straight leg raising weakness in the 0.1% concentration group vs 66.7% in the 0.2% concentration group, and the difference was significant (p=0.027). DISCUSSION: We concluded that with the same dose of ropivacaine, 0.1% concentration was associated with less motor block but similar sensory block and degree of labour analgesia as compared to the 0.2% concentration.