How is anesthesia administered to a rat? - briefly
Anesthesia for a rat is typically induced either by inhalation of volatile agents (e.g., isoflurane delivered through a calibrated vaporizer) or by intraperitoneal injection of injectable combinations such as ketamine‑xylazine, with doses calculated per kilogram of body weight. Continuous monitoring of respiratory rate and reflexes ensures adequate depth throughout the procedure.
How is anesthesia administered to a rat? - in detail
Anesthetizing a laboratory rat requires precise selection of agents, accurate dosing, proper equipment, and continuous physiological monitoring.
The most common approaches are inhalation and injectable methods.
Inhalation anesthesia
- Agent: Isoflurane or sevoflurane delivered via a vaporizer.
- Induction chamber: Small, airtight enclosure with a transparent lid for visual observation.
- Flow rate: 1–2 L/min of carrier gas (oxygen or air) with 2–5% volatile anesthetic for induction, reduced to 0.5–1.5% for maintenance.
- Scavenging system: Connects to a charcoal filter or active suction to prevent exposure to personnel.
- Monitoring: Respiratory rate, pedal withdrawal reflex, and body temperature.
Injectable anesthesia
- Agent: Ketamine‑xylazine, medetomidine‑midazolam, or urethane, depending on experimental duration and depth required.
- Dose calculation: Body weight (g) × recommended mg/kg (e.g., ketamine 80 mg/kg + xylazine 10 mg/kg).
- Injection site: Intraperitoneal (IP) or subcutaneous (SC) using a 27‑ gauge needle.
- Volume: Not exceeding 0.5 mL per 100 g to avoid abdominal distension.
- Onset: 5–10 minutes after IP injection; 10–15 minutes after SC injection.
- Maintenance: Supplemental bolus of half the induction dose if reflexes return.
- Reversal: Atipamezole (0.1 mg/kg) for medetomidine or yohimbine (2 mg/kg) for xylazine, administered IP.
Preparation and safety
- Weigh each animal to the nearest gram before dosing.
- Prepare anesthetic solutions under a fume hood; label with concentration, agent, and expiration time.
- Use sterile syringes and needles; discard after single use.
- Warm the animal on a heating pad (37 °C) during induction to prevent hypothermia.
- Record baseline heart rate and respiration before anesthesia.
Physiological monitoring
- Pulse oximetry probe placed on the tail or paw to track oxygen saturation.
- Rectal thermometer to maintain core temperature between 36.5–37.5 °C.
- Reflex checks: toe pinch for surgical plane, corneal reflex for deeper anesthesia.
- Adjust vaporizer settings or administer supplemental injection based on observed signs.
Recovery
- Transfer the rat to a clean, warm recovery cage with soft bedding.
- Continue temperature support until the animal regains sternal recumbency.
- Observe for normal grooming and ambulation before returning to the home cage.
- Document total anesthetic time, doses administered, and any adverse events.
Following these steps ensures reproducible anesthetic depth, minimizes physiological disturbance, and complies with institutional animal care guidelines.