Direction of the Whitacre 26G needle aperture and level of subdural blockade achieved by ropivacaine 0.75% in planned caesarean section

ABSTRACT

The scope of this study was to investigate if changing the direction of the Whitacre 26G needle aperture in regional anaesthesia during planned caesarean section produces a difference in the dose-response curves of the level of subdural blockade achieved by ropivacaine 0.75% and a standard dose of opioid. One hundred and twenty healthy parturients were blindly randomised in two groups, with 5 subgroups of 12 women each. In Group K (n=60) the direction of the needle was cephalad and the injected doses of ropivacaine 0.75% were 7.5, 8.25, 9, 9.75 and 10.5 mg. In group O, the direction of the needle was caudal and the injected doses of ropivacaine 0.75% were 12.75, 13.5, 14.25 and 15 mg. In all subjects we added 0,015 mg fentanyl in the solution. We recorded the level of the blockade achieved and a linear regression analysis was used in respect to the injected dose. In group O, there was a significant statistical correlation (p=0.047) between the level of subdural blockade achieved (R2=0.064) and the dose injected. In group K, there was no such correlation (R2=0.0009). The cephalad administration of ropivacaine in doses between 7.5-10.5 mg achieved a mean blockade above T4 level, whereas, when caudal injection was used, the doses needed were above 14.4 mg. In conclusion, the level of blockade produced by subdural injection of ropivacaine 0.75% during caesarean section is correlated with the cephalad or caudal direction of the aperture of the Whitacre 26G needle.