Lidocaine permeability in silicone tissue expanders: an in vitro analysis.

Tissue expansion has achieved a prominent role in soft-tissue reconstruction. Expansion-induced pain is often a limiting factor in this process and can affect patients for as long as 24 to 48 hours following each expansion session. Although lidocaine is known to be an effective analgesic, only anecdotal reports of its usefulness when placed within a tissue expander currently exist. This two-part study was designed first to determine if in fact silicone is readily permeable to lidocaine, and second to determine if the potential diffusion dynamics can be defined. In part 1 of the study, the silicone polymer was indeed found to be readily permeable to lidocaine as measured with fluorescence immunoassay technique. In part 2, two groups of Surgitek and Dow Corning expanders were filled with saline and lidocaine and placed in saline baths. At several intervals over a 48-hour period, aliquots of the surrounding saline were sampled and the lidocaine levels subsequently determined. A rather predictable and consistent diffusion curve was demonstrated. The significant difference in diffusion characteristics between the two expander types was apparently due to wall thickness differences inherent in the manufacturing. In this in vitro study, filler-valve leakage did not significantly contribute to lidocaine migration from within these tissue expanders. This basic in vitro work will now set the stage for further in vivo and clinical investigations to more precisely define the role of lidocaine in the tissue-expansion process.