PubMed · 8686813
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M G Wertkin. 1996. Needle localization biopsy.. https://pubmed.ncbi.nlm.nih.gov/8686813/
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OBJECTIVES: To characterize the uptake, washout, and metabolism of lidocaine hydrochloride in the iris/ciliary body and cornea. METHODS: Iris/ciliary body uptake of lidocaine hydrochloride was measured by incubating human and rabbit irides in radiolabeled carbon 14-1% lidocaine hydrochloride for 2 to 60 minutes. Washout was determined by incubating the iris in 14C-1% lidocaine hydrochloride for 5 minutes and transferring the iris to a series of wells. The wells contained a common intraocular irrigating solution of essential ions, glucose, and glutathione buffered with bicarbonate (an enriched balanced salt solution [BSS PLUS]), which is similar to aqueous humor. Corneal uptake was measured by exposing the endothelial surface to 14C-1% lidocaine hydrochloride for 5 or 15 minutes. Corneal washout was performed after 5-minute exposure to 14C-1% lidocaine hydrochloride using a 2-chambered diffusion apparatus. Samples of the iris, cornea, and BSS PLUS washout solution were analyzed by high-performance liquid chromatography and liquid scintillation spectrometry. RESULTS: In vitro iris/ciliary body uptake of 14C-1% lidocaine hydrochloride follows a logarithmic curve, with 50% to 60% of maximum lidocaine hydrochloride uptake present at 5 minutes. There was no difference in uptake between human, albino rabbit, and pigmented rabbit irides. Washout of lidocaine from the iris occurs with a halflife of 8 to 9 minutes. Corneal uptake of lidocaine was greater after incubation for 15 vs. 5 minutes. The washout of lidocaine from the cornea had a half-life of 5 minutes. Results of high-performance liquid chromatography confirmed that there were no metabolites or breakdown products in the iris, cornea, or washout solution. CONCLUSIONS: Lidocaine is taken up quickly by the iris/ ciliary body and cornea and rapidly removed from these tissues after BSS PLUS washout. Irrigation during phacoemulsification seems to limit lidocaine exposure to the ocular tissues, resulting in a short duration of anesthesia. Lidocaine is not metabolized or broken down by the iris or cornea during this short period.
This technique is a safe simple way to administer sub-Tenon's anesthesia that provides akinesia comparable to that of retrobulbar and peribulbar anesthesia and frequently results in excellent lid block. The potentially serious complications associated with retrobulbar and peribulbar methods appear to be absent.
PURPOSE: To determine the distribution of anesthetic fluid during 3 regional anesthetic techniques routinely used for phacoemulsification. METHODS: Patients having routine cataract extraction by phacoemulsification were studied after informed consent had been obtained. B-scan ultrasonography was performed on the eye before administration of the anesthetic agent. Kinetic echography was used to scan the eye during administration of the anesthesia to show the needle position and location of fluid in the orbit during the injection. Ten minutes after injection, another scan was performed to outline the pattern of fluid distribution. RESULTS: In all patients, the needle and the anesthetic fluid were seen on ultrasonography, with sub-Tenon's the most easily seen. In the sub-Tenon's group, fluid tracked behind the globe in the retrobulbar space, appearing as a dark outline during the injection. The fluid around the optic nerve developed a characteristic T sign. In the retrobulbar technique, the needle was less easily identifiable and fluid localized within the cone. The fluid distributed in the intraconal fat. Identification of the peribulbar needle and fluid was also more difficult; the fluid was, however, seen in the extraconal fat. After 10 minutes, fluid was seen within the cone. CONCLUSION: B-scan ultrasonography was a suitable method of identifying the needle position and the distribution of anesthetic fluid in regional ocular anesthesia. The sub-Tenon's technique appears to be the safest method of introducing anesthetic fluid into the retrobulbar space without the potential complications of sharp-needle techniques.