How should a rat’s ear be rinsed? - briefly
Use sterile, lukewarm saline delivered with a soft pipette or syringe, directing the flow gently into the external canal while avoiding pressure on the tympanic membrane. Pat the canal dry with a sterile gauze pad immediately after flushing.
How should a rat’s ear be rinsed? - in detail
Proper ear irrigation in a laboratory rat requires sterile equipment, gentle handling, and precise technique to avoid damage to the delicate auditory canal.
First, gather the following items: sterile saline solution (0.9 % NaCl, body‑temperature), a 1 ml syringe with a 22‑gauge soft‑tip catheter, cotton swabs without applicator, disposable gloves, and a clean work surface. Verify that the saline is warmed to approximately 37 °C; cold fluid can cause vasoconstriction, while hot fluid may burn the tissue.
Place the rat in a restraining device that secures the head without applying pressure to the ears. Apply a mild anesthetic spray to the external ear if required by the protocol, allowing 1–2 minutes for onset. Hold the ear upright with a gloved thumb and forefinger, exposing the canal entrance.
The irrigation steps are:
- Fill the syringe with warmed sterile saline, ensuring no air bubbles remain.
- Insert the catheter tip gently into the ear canal, advancing no more than 2–3 mm; the tip must not touch the tympanic membrane.
- Depress the plunger slowly, delivering 0.2–0.3 ml of fluid in a steady stream. The fluid should flow toward the external opening, carrying debris outward.
- Withdraw the catheter while maintaining slight pressure on the ear to prevent fluid backflow.
- Use a dry cotton swab to absorb excess fluid from the outer ear; avoid inserting the swab into the canal.
Repeat the process on the opposite ear if necessary, using a fresh catheter for each side. After irrigation, inspect the canal with a magnifying lens. Look for residual wax, blood, or signs of irritation. If any debris remains, repeat the rinse with a reduced volume (0.1 ml) to minimize trauma.
Finally, monitor the rat for 10–15 minutes for signs of discomfort, excessive scratching, or discharge. Document the volume of saline used, any observations of canal condition, and any adverse reactions. Proper record‑keeping ensures reproducibility and animal welfare compliance.