Crystallization of local anesthetic mixtures with adjuvants and the effect of micropore filtration.

Abstract

Regional anesthesia is widely used in pain management to reduce opioid requirements, enable early mobilization and improve postoperative outcomes. However, commonly used combinations of local anesthetics and adjuvants can crystallize under clinical conditions, which generates concerns regarding neurotoxicity and embolization complications. This study aimed to determine whether microporous filters can effectively eliminate crystals formed by mixing local anesthetics and adjuvant. Commonly used local anesthetics (lidocaine, mepivacaine and ropivacaine) and adjuvants (dexamethasone, dexmedetomidine and sodium bicarbonate) were combined and tested. The mixture was passed through 5 µm and 0.2 µm filters, and the presence of crystals before and after filtration at specific time points and volumes was assessed microscopically. Lidocaine mixtures showed no detectable crystallization under any condition. In contrast, crystallization occurred in most combinations containing mepivacaine or ropivacaine, with the highest grades observed in ropivacaine-bicarbonate mixtures (grade 5). Filtration reduced crystallization grades by 1-3 points depending on the mixtures, but did not eliminate crystals in most mixtures. Crystals also persisted after longer intervals and with larger filtration volumes. No meaningful difference was observed between the 5 µm and 0.2 µm filters. Crystallization can occur in anesthetic-adjuvant mixtures that are commonly used for regional anesthesia. Although filtration reduces these crystals, it does not eliminate crystals, especially those with large volumes or unstable combinations.