Why does having a spinal block cause low blood pressure?
WWD beat me to the punch! When we do neuraxial blocks (epidurals and spinals), we block a variety of nerves. The thinnest nerves are the ones that get blocked first – sympathetic nerves, temperature and vibration sensation are the ones that are affected. Sensation and then motor nerves are blocked next. Loss of sympathetic tone causes vasodilation, and a drop in blood pressure. We try to minimize this by running a lot of fluid in quickly, but sometimes we can’t “fill the tank” quickly enough. I like to see a *little* drop in BP after the spinal goes in so I know it’s starting to work. (Although we sometimes put opiates in spinals, the main medication is a local anesthetic, or numbing drug.
