[Gas diffusion in the middle ear during anesthesia for tympanoplasty]

Area of Science:

• Anesthesiology
• Otolaryngology
• Middle Ear Physiology

Context:

• Nitrous oxide (N2O) anesthesia is known to increase middle ear pressure (MEP) due to gas diffusion.
• Elevated MEP can lead to complications such as hearing loss and tympanic membrane rupture, particularly during tympanoplasty.
• Previous research since 1965 has documented the issue of gas diffusion into the middle ear under anesthesia.

Purpose:

• To investigate an alternative anesthetic technique to mitigate middle ear gas loading during tympanoplasty.
• To evaluate the efficacy of substituting nitrous oxide with ethrane and air in preventing middle ear pressure increase.
• To determine the impact of controlled partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2) on gas diffusion.

Summary:

• A modified anesthetic approach using ethrane, supplemented with narcotics and muscle relaxants, was employed for tympanoplasty.
• This technique successfully reduced middle ear gas diffusion, maintaining middle ear pressure below 0.68 kPa (70 mm H2O).
• Controlled ventilation, keeping PaO2 below 17.9 kPa (135 mm Hg) and PaCO2 at 3.9 kPa (30 mm Hg), was crucial for minimizing diffusion, with higher PaCO2 levels correlating to increased diffusion.

Impact:

• Provides a safer anesthetic management strategy for patients undergoing middle ear surgery, reducing the risk of barotrauma.
• Offers a practical solution to a long-standing problem in anesthesiology and otologic surgery.
• Highlights the importance of meticulous control of respiratory parameters during anesthesia to protect middle ear integrity.