Anesthesia Guidelines: Rats

Find guidelines for rat anesthesia, including anesthetic drugs and procedures.

Research Animal Resources (RAR) veterinary staff designed these guidelines to be general recommendations, not an inclusive list of all possible drug combinations that can be used in rats. Consequently, guidelines do not reference specific research-associated concerns. 

If you have questions about using anesthetics for your particular situation, please work with your area veterinarian to develop the most effective anesthetic plan.


How to use anesthesia

Animals may be anesthetized for surgery, for non-surgical procedures that may be painful, or non-painful procedures that require immobilization. Anesthesia is the loss of feeling in all or part of the body, with or without loss of consciousness.  

Steps must be taken before, during, and after anesthesia to ensure animal safety and anesthesia efficacy. 

Anesthetic drugs can be administered parenterally or by inhalation. The choice of anesthetic agent will depend on the procedure to be performed, research aims, and other factors such as animal age.  Consult your area veterinarian with questions about drug selection.


General guidelines and considerations for rat anesthesia

Acclimation

A one-week acclimation period is recommended for all animals to prevent stress-induced disease.

Fasting 

Pre-anesthetic fasting is usually not necessary for rats due to their inability to vomit. However, if fasting is employed limit to no more than two to three hours due to the high metabolic rate of small rodents. Never restrict water.

Eye protection 

Rat eyes remain open under anesthesia. This can lead to corneal drying and trauma. Apply ophthalmic ointment (e.g., Paralube® or Lacrilube®) if:

  • The anesthetic event lasts longer than five minutes.
  • Anesthesia is being delivered by facemask. 

Monitoring 

Regardless of the anesthetic administered, monitor rats under anesthesia to avoid excessive depression of cardiac and respiratory functions, or insufficient anesthesia. Parameters that can be monitored in an anesthetized rat without specialized equipment include:

  • Anesthetic depth: Toe pinch. 
  • Respiratory rate and pattern: The normal undisturbed rate is ~70-120/min, a slow rate drop of 50% is acceptable during anesthesia.
  • Mucous membrane color: Should be pink not blue or gray.
  • Body temperature: Can be monitored with a rectal thermometer, and should be between 96.5-99.5°F.
  • Oxygen saturation and heart rate: Can be monitored using a specialized rodent pulse oximeter, and should be greater than 95% and between 300-550, respectively. 

Heat support

All species are at risk for hypothermia while under anesthesia. Rats are particularly susceptible due to their high body surface area to body mass ratio. Hypothermia induces a significant physiological stress on animals that can prolong recovery and potentially be fatal. Guidelines:

  • Provide supplemental heat during all anesthetic events. Supplemental heat sources include circulating water blankets, electric heating pads, and commercial products that can be warmed in a microwave.  
  • Never place the animal directly on the heat source.  

Fluid support

Consider providing warm subcutaneous (SQ) or intraperitoneal (IP) fluids, particularly for prolonged anesthetic events or animals that are ill, aged, or debilitated. 

Recovery

Continue to monitor animals until they are fully recovered. Guidelines: 

  • Recover animals on paper towels (without bedding) in a clean cage. This minimizes the risk of tracheal obstruction or pneumonia.
  • Recover anesthetized animals alone in a cage.
  • Continue to provide supplemental heat during recovery.
  • When the animal is ambulatory, return it to the home cage with immediate access to food and water.

Contact your area veterinarian with questions or for additional information.


Anesthetic drugs and procedures

Inhaled anesthetics

Inhaled anesthetics

Isoflurane is the preferred inhaled anesthetic. It has rapid and reliable onset and recovery. Inhalation anesthesia may be delivered by:

Drop jar: Do not allow the rat to come into direct contact with the liquid inhalant anesthetic (which can be achieved by placing a mesh grid over the cotton/gauze). Because the anesthetic concentration cannot be controlled in the chamber and can rapidly reach toxic concentrations, this method is reserved for very short procedures such as subcutaneous tumor implantation or induction prior to facemask anesthesia. 

Induction chambers, facemasks and endotracheal tubes: These require gas anesthesia machines with an oxygen source and a precision vaporizer. The vaporizer must be compatible with the specific inhaled anesthetic agent. Due to the small respiratory capacity in rats, use a non-rebreathing system.

When using inhalant anesthesia, use a fume hood or an anesthetic system equipped with a gas scavenging system to minimize occupational exposure to exiting gases.


Isoflurane – recommended

Dose: 4-5% for induction; 1-2% for maintenance
Comments: 300μL in a 500ml container for drop jar anesthesia

Injectable anesthetics

Injectable anesthetics

Combined ketamine/xylazine is the preferred injectable anesthetic in rats. Other commonly used injectable agents are listed below. 

Key considerations

  • Rats vary significantly in their sensitivity to various anesthetics. Age, body composition, strain, health status, genetic manipulation, and sex are just a few of the factors that can contribute to anesthetic sensitivity. The following doses are general guidelines that may vary significantly based on the aforementioned factors. When adding anesthetics to your protocol, it is advisable to provide a range to allow titration for the specific needs of each animal.
  • Intramuscular (IM) injections are not recommended in rats as complications such as tissue irritation, lameness, and self-mutilation can result.

Ketamine + xylazine (Rompun®) – recommended

Dose: Ketamine: 40-90 mg/kg + xylazine 5-10 mg/kg
Route: Intraperitoneal  (IP)
Duration of anesthesia: 45-90 minutes
Comments: Thermal support is crucial. If additional anesthetic is needed, supplement with 1/3 dose of ketamine only. Xylazine can be reversed with 1 - 2 mg/kg yohimbine IP or 0.1 - 1.0 mg/kg atipamezole IP/SQ.


Ketamine + diazepam (Valium®)

Dose: Ketamine: 40-80 mg/kg + Diazepam: 5-10 mg/kg
Route: IP
Duration of anesthesia: 20-30 minutes


Pentobarbital (Nembutal®)

Dose: 40-50 mg/kg
Route: IP
Duration of anesthesia: 80-90 minutes
Comments: Dose sufficient to produce surgical anesthesia may cause severe respiratory depression and death. Administer diluted in saline (<10 mg/ml). Avoid buprenorphine co-administration. Buprenorphine and Pentobarbital will result in cardiorespiratory depression. Administer buprenorphine after full recovery.


Alpha-chloralose – not recommended

Dose: 30-65 mg/kg
Route: IP
Duration of anesthesia: Unproven
Comments: Poor analgesia, possible convulsions, metabolic acidosis. Do not use for survival surgical procedures.


Chloral hydrate – not recommended

Dose: 300-450 mg/kg
Route: IP
Duration of anesthesia: Unproven
Comments: Concentration above 5% produce peritonitis. Anesthetic dose is near the lethal dose. Do not use for surgical procedures.

Local anesthetics

Local anesthetics

Local anesthetics are a type of injectable anesthetic. Local anesthetics block nerve impulses by specifically binding the voltage‐gated Na+ channel in the nerve cell membrane.

Routes of administration include topical to mucous membranes (nose, eye, etc.), or injected directly into tissues and around nerve bundles.

Key considerations

  • Administration of local anesthetics prior to the painful stimulus (e.g., incision) would be considered an adjunct analgesic to opioid and NSAID analgesics. 
  • Use as a primary analgesic is discouraged due to the short duration (hours).
  • Lidocaine has a quick onset (1-2 minutes), but is short acting (1-2 hours). Bupivacaine is slow onset (10-15 minutes), but is long acting (4-8 hours). When used in combination (lidocaine plus bupivacaine in the same syringe) local anesthesia can be fast onset with a relatively long duration of action.
  • For rodent use, dilute 1‐2% lidocaine to 0.5% and 0.5% bupivacaine to 0.25% to allow for feasible volumes to infuse at the incision site (1% solution is equal to 10 mg/mL).

Lidocaine

Dose: 4 mg/kg (0.4 mL/kg of a 1% solution)
Route: Local infiltration
Comments: Do not exceed 7 mg/kg total dose. Rapid onset, short duration


Bupivacaine

Dose: 1-2 mg/kg (0.4-0.8 mL/kg of a 0.25% solution)
Route: Local infiltration
Comments: Do not exceed 6 mg/kg total dose. Slower onset, longer duration

 

References for these guidelines are available by request.