I know that there would be zillions of these performed everyday but if it was me I think, and given a choice, I'd rather be knocked out completely than have a needle shoved in my spine, whether for a birth or some other medical condition.
The following link is to a news article about a mum in Sydney, Australia. http://news.ninemsn.com.au/national/7948729/mother-giving-birth-injected-with-poison.
What can be said when things go this wrong?