Adding anesthetic to the injectate may provide several benefits: it increases muscle relaxation, it supplies a psychological benefit from immediate pain relief, and it purportedly breaks the pain-muscle spasm-ischemia-pain cycle (23). If a less concentrated dose of the anesthetic is chosen, occasionally there can be partial anesthesia of the dura, but rarely a significant motor or sensory block (5,24).
It is important to note that methyl paraben- or phenol-containing anesthetics can cause flocculation of depot steroid preparations (68). For these reasons, we inject preservative-free 0.5% lidocaine. El-Khoury et al. (5) reported no known interaction or flocculation in mixing contrast with the medications. We eschew bupivicaine and other longer-acting anesthetics to limit the duration of the occasional case of a significant block from a lumbar ESI. If bupivicaine is chosen, it should be 0.25% (24).
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