Effects of topical anesthetics on tympanic membrane structure

Area of Science:

• Otolaryngology
• Anesthesiology
• Biomaterials Science

Background:

• Topical local anesthetics offer an alternative to general anesthesia or invasive techniques for otologic procedures.
• Myringotomy and tympanostomy tube insertion are common procedures requiring effective pain management.
• Understanding the structural effects of topical agents on the tympanic membrane is crucial for clinical application.

Purpose of the Study:

• To compare the effects of tetracaine base in dimethylsulfoxide (DMSO), pure DMSO, and Bonain's solution on the tympanic membrane structure in a guinea pig model.
• To evaluate the regenerative capacity of the tympanic membrane following topical anesthetic application.

Main Methods:

• Guinea pigs were treated with topical agents (tetracaine base/DMSO, DMSO alone, Bonain's solution) and observed for survival times ranging from 1 day to 3 months.
• Tympanic membranes were harvested, embedded, sectioned, and analyzed histologically.
• Infected specimens with external otitis were excluded to prevent confounding results.

Main Results:

• Bonain's solution caused rapid epithelial and mucosal loss within 1 day and severe connective tissue hyperplasia by 1 month.
• Tetracaine base in DMSO resulted in epithelial and mucosal cell loss within 3 days, but regeneration began within 7 days.
• Complete structural restitution of the tympanic membrane was observed after 3 months in the tetracaine base or DMSO groups.

Conclusions:

• Bonain's solution demonstrates significant toxicity to the tympanic membrane structure.
• Tetracaine base in DMSO appears to be a safer topical anesthetic option, allowing for tympanic membrane regeneration.
• Topical tetracaine base in DMSO may be a viable alternative for pain management in otologic procedures without causing permanent structural damage.