Implications of dexamethasone and ropivacaine in peripheral nerve blocks

Brooke A. Tow

Abstract

Background: Nerve blockades are integral to prevent complications and speed recovery after surgery. Adding a steroid such as dexamethasone to a local anesthetic such as ropivacaine is known to prolong the anesthetic effect, provide a faster onset of action of the anesthetic, and reduce the use of opioids post- operatively. However, the admixture crystalizes rapidly and causes patient safety and storage issues. The crystals impose a risk of serious neurological adverse events like spinal cord injury, paralysis, and even death should they inadvertently embolize. Though it is known that the admixture crystallizes at high concentrations, there remains a gap in the knowledge regarding the crystallization of the nerve blocks at lower concentrations used at this institution and peer institutions around the country.
Methods: In order to test the degree of crystallization of ropivacaine and dexamethasone, we prepared syringes mirroring the two formulations of nerve blocks as utilized at our institution: transversus abdominis plane blocks and interscalene or adductor canal blocks. We also prepared a control of each nerve block formulation containing sodium bicarbonate instead of the dexamethasone, since this solution would be expected to crystalize. We tested the pH of each solution as well as examined the wet mounts under a microscope using 20× magnification to check visually for crystals at time (t) =1 minute, 10 minutes, 60 minutes, 120 minutes, and 24 hours.
Results: Crystals were detected within minutes in all of the mixtures studied. The controls had crystals that were macroscopically visible instantaneously after mixed. When the crystals were rechecked at a later time point, there did not seem to be a noticeable change in crystal number or size. Crystals formed near instantaneously and did not appear to increase in number over time.
Conclusions: Our experiment suggests that current anesthetic practice needs to be reassessed and altered. The ropivacaine and dexamethasone combination rapidly crystalizes even at very low concentrations of dexamethasone. Though dexamethasone is a non-particulate steroid that can be used for intravascular injection, our results suggest that the combination of the dexamethasone and ropivacaine should be regarded as a particulate steroid, and carry the same risks of intravascular administration as particulate steroids.