Anesthesia Guidelines: Guinea Pig

Guidelines for guinea pig anesthesia, including recommended anesthetic drugs and procedures.


General considerations

Acclimation

A one week acclimation period is recommended for all animals to prevent stress-induced disease. Guinea pigs are easily stressed by handling and should be habituated to handling.

Fasting

Fasting should be performed for 2-3 hours prior to anesthesia to reduce the amount of ingesta in cecum and stomach. Exceptions to this include debilitated animals, young animals, and animals during late pregnancy. Water should never be restricted.

Guinea pigs will store feed in their cheeks and this can lead to airway obstruction. To reduce the amount of material stored in the cheeks the mouth should be gently rinsed with tap water (10-20 ml) prior to induction. The inside of the cheek can also be gently swabbed with a cotton-tipped applicator to remove any remaining material.

Eye protection

Guinea pig eyes remain open under anesthesia. This can lead to corneal drying and trauma.

Ophthalmic ointment (e.g., Paralube® or Lacrilube®) must be applied to eyes if:

  • The anesthetic event lasts longer than 5 minutes.
  • Anesthesia is being delivered by facemask.

Monitoring

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

  • Anesthetic depth: jaw tone and/or palpebral reflex. In guinea pigs, toe pinch can be unreliable and is not a recommended method.
  • Respiratory rate and pattern: The normal undisturbed rate is ~40-100/min; a slow rate drop of 50% is acceptable during anesthesia
  • Mucous membrane color: Pink, not blue or grey
  • Body temperature: Rectal thermometer, > 98 °F.
  • Cardiovascular parameters: Oxygen saturation (>95%) and heart rate (240-350 beats/min) can be monitored using a specialized rodent pulse oximeter.
  • Contact your area veterinarian with questions about monitoring or monitoring equipment.
  • Please refer to IACUC guidelines for anesthetic monitoring.

Heat support

All species are at risk for hypothermia while under anesthesia. Guinea pigs 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.

Provide supplemental heat during all anesthetic events.

  • Supplemental heat sources include circulating water blankets or commercial products that can be heated up or create heat via a safe chemical reactions. NO electric heating pads are allowed for use with guinea pigs.

Never place the animal directly on the heat source.

Contact your area veterinarian with questions about using or purchasing supplemental heat sources.

Fluid support

Consider providing warm SQ or IP fluids, particularly for prolonged anesthetic events or animals that are ill, aged, or debilitated. Consult your veterinarian.

Recovery

Continue to monitor animals until they are fully recovered.

  • 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.
  • It is important for guinea pigs to eat as soon as possible post-operatively to decrease the occurrence of ileus. A small amount of treats (apples, leafy vegetable, carrots) or syringe-fed critical care diet may aid in promoting post-operative eating. Please speak with your area veterinarian regarding appropriate supportive nutrition and how to provide.

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 a chamber, facemask or intubation.

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 guinea pigs use a non-rebreathing system.
  • When using inhalant anesthesia, a fume hood or an anesthetic system equipped with a gas scavenging system must be used to minimize occupational exposure to exiting gases.

**Guinea pig intubation is difficult due to their anatomy, thus intubation is generally not recommended in guinea pigs. If intubation is necessary due to experimental design, please contact your area veterinarian for consultation.

Due to the large volume of the gastrointestinal tract of guinea pigs, the weight of the cecum on the diaphragm can often cause apnea during inhalation anesthesia. This can be minimized by placing rolled towels under the animal’s chest so that the gastrointestinal organs are not in direct contact with the diaphragm, or tilting the table if possible.


Isoflurane (Recommended)

Dose: 4-5% for induction; 1-2% for maintenance

Injectable Anesthetics

Injectable Anesthetics

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

Guinea pigs 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 guinea pigs as complications such as tissue irritation, lameness, and self-mutilation can result. If IM injections are necessary per experimental design, please contact your area veterinarian for consultation and training.


Ketamine + Xylazine (Recommended)

Dose: 50 mg/kg ketamine and 5 mg/kg xylazine
Route: IP
Duration of Anesthesia: 60-90 minutes
Comments: Thermal support is crucial. To prolong anesthesia, 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


Pentobarbital (Nembutal®)

Dose: 15-30 mg/kg
Route: IP
Duration of Anesthesia: 30-60 minutes
Comments: Causes respiratory depression; narrow margin of safety. Use with caution.


Ketamine + Dexmedetomidine

Dose: 40 mg/kg ketamine and 0.25 mg/kg dexmedetomidine
Route: IP
Duration of Anesthesia: 20-30 minutes


Ketamine + Diazepam

Dose: 20-50 mg/kg ketamine and 3-5 mg/kg diazepam
Route: IP


Local Anesthetics

One type of injectable anesthetic is a local 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 mucus membranes (nose, eye, etc.) or injected directly into tissues and around nerve bundles.
  • Administration of local anesthetics prior to the painful stimulus (eg. 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: 2-4 mg/kg (0.4 mL/kg of a 1% solution)
Route: Local infiltration
Comments: Local infiltration Do not exceed 7 mg/kg total dose

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


References

  • Carpenter JW: Exotic Animal Formulary 3rd edition. Elsevier Saunders 2005.
  • Maureen Hargaden and Laura Singer. Chapter 20 in The Laboratory Rabbit, Guinea Pig, Hamster, and Other Rodents. 2012, Pages 575-602.
  • Laboratory Animal Medicine, 2nd edition. Fox, JG et al. editors. Academic Press, 2002.
  • ULAM Guinea Pig Anesthesia and Analgesia Guidelines. https://wiki.umms.med.umich.edu/display/public/ULAMGSOP/Guidelines+on+An....