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To evaluate at which pH level various local anesthetics precipitate, and to confirm which combination of corticosteroid and local anesthetic crystallizes.
Each of ropivacaine-HCl, bupivacaine-HCl, and lidocaine-HCl was mixed with 4 different concentrations of NaOH solutions. Also, each of the three local anesthetics was mixed with the same volume of 3 corticosteroid solutions (triamcinolone acetonide, dexamethasone sodium phosphate, and betamethasone sodium phosphate). Precipitation of the local anesthetics (or not) was observed, by the naked eye and by microscope. The pH of each solution and the size of the precipitated crystal were measured.
Alkalinized with NaOH to a certain value of pH, local anesthetics precipitated (ropivacaine pH 6.9, bupivacaine pH 7.7, and lidocaine pH 12.9). Precipitation was observed as a cloudy appearance by the naked eye and as the aggregation of small particles (<10 µm) by microscope. The amount of particles and aggregation increased with increased pH. Mixed with betamethasone sodium phosphate, ropivacaine was precipitated in the form of numerous large crystals (>300 µm, pH 7.5). Ropivacaine with dexamethasone sodium phosphate also precipitated, but it was only observable by microscope (a few crystals of 10–100 µm, pH 7.0). Bupivacaine with betamethasone sodium phosphate formed precipitates of non-aggregated smaller particles (<10 µm, pH 7.7). Lidocaine mixed with corticosteroids did not precipitate.
Ropivacaine and bupivacaine can precipitate by alkalinization at a physiological pH, and therefore also produce crystals at a physiological pH when they are mixed with betamethasone sodium phosphate. Thus, the potential risk should be noted for their use in interventions, such as epidural steroid injections.
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In this article, we report a case where a videofluoroscopic swallowing study (VFSS) revealed the cause of a recently developed idiopathic dysphagia in a 66-year-old patient and enabled emergent treatment. The patient reported a 10-day history of fever, cough, sputum production, and progressive jaundice. He was then admitted to the hospital with suspicion of aspiration pneumonia. Despite treatment with antibiotics, fever and leukocytosis were persistent. As he also reported dysphagia, we performed the VFSS, which showed subglottic aspiration on all types of food and revealed a retropharyngeal mass causing mechanical compression. A contrast-enhanced computerized tomography (CT) of his neck was performed following the VFSS, which helped diagnose the mass as an extensive retropharyngeal abscess with mediastinitis. Following this diagnosis, emergent surgical incision and drainage was performed on the patient. Although the VFSS is primarily designed to evaluate swallowing function rather than to diagnose a disease, it can be used to reveal the primary medical cause of dysphagia while it studies the mechanical and structural abnormalities in the oropharyngeal and esophageal regions. This study also proposes that retropharyngeal abscess should be considered in the differential diagnosis of cases showing progressive dysphagia with fever. As confirmed through this work, the VFSS can function as a useful tool for detecting crucial diseases accompanying deglutition disorder.
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