Anesthesia and Analgesia: Neonatal Mice and Rats

BU IACUC Approved January 7, 2011, Reviewed July 2019

Neonates are defined as mouse or rat pups up to 10 days of age.

Gas anesthesia (isoflurane) or hypothermia may be used to anesthetize neonatal rats and mice. Parenteral agents are not advisable in very young animals. Hypothermia allows less control of anesthetic depth compared to inhalant anesthesia. Hypothermia is appropriate for short, minor surgical procedures (5-15 minutes) in neonatal rats or mice up to 5 days of age. Gas anesthesia is recommended for longer, more invasive procedures and in neonates older than 5 days. Very young hairless, altricial rodents function as poikilotherms and are resistant to brain damage associated with cephalic circulatory arrest. Surface cooling is effective due to their small surface area and body size. Hypothermia provides immobilization and mild analgesia (similar to local anesthesia resulting in nerve transmission blockage). For more information contact veterinary staff for assistance.


A. Neonates must be anesthetized for painful procedures and surgery.

B. Analgesia

Neonates must receive analgesia if the procedure can reasonably be expected to result in enough pain to interfere with the neonatal function of sleeping and suckling. Exceptions may be considered, if the disturbance of neonate and dam in order to administer the medication interferes more than warranted with these functions.

C. Documentation

Documentation is required for neonatal anesthesia, surgery and postoperative care. Please use the IACUC Anesthesia and Surgical Monitoring Form for Rodents or a substantially similar form.


A. Recommended Preparation of Dam Prior to Recovery Anesthesia and Surgery on Neonates1.


B. Hypothermia 1


C. Recovery of Neonate from Hypothermia


D. Preparing the Neonate for Return to Dam


E. Inhalant Anesthesia Isoflurane Method

Inhalant anesthesia may be safe both for ultra short (<5 minutes=”” and=”” prolonged=”” greater=”” than=”” 6=”” hours=”” procedures=”” for=”” longer=”” periods=”” of=”” anesthesia=”” it=”” may=”” be=”” necessary=”” to=”” ventilate=”” the=”” animal=”” sup=””>2, 6, 7

  1. Induce anesthesia in an induction box.
  2. Use an adult mouse facemask adjusted for neonate. Or use the EZ-103A Microflex Breather and shave off a small amount to shorten the mask to fit the neonate. 5
  3. Administer isoflurane at 1.5 – 2.5% in 100% oxygen.
  4. Place neonate on warm pad or circulating warm water pad.
  5. During the recovery phase, turn off inhalant gas before oxygen.

Inhalant Anesthesia (Isoflurane) for Neonatal Rats and Mice

Phase of AnesthesiaOxygen L/minIsoflurane %
Induction0.5 – 1.04-5
Maintenance0.5 – 1.01-2
Recovery0.5 then to O*0

* During the recovery phase, turn off inhalant gas before oxygen.

F. Parenteral (Injectable) Anesthetics

G. Preemptive and/or Postoperative Analgesia

Analgesic Agents for Neonatal Rats and Mice

Administer a lower dose then would be administered to adult animals to start with. These opioids have been shown to be safe and effective analgesics in neonatal rodents.3

* Handling of neonates should be minimized.

DrugSpeciesDose mg/kgRoute and needle size (gauge)Max. volume
BuprenorphineMOUSE0.05-0.5IP or SC <27 g=”” td=””><0.2Every 6-8 hours
BuprenorphineRAT0.01-0.05IP or SC <25 g=”” td=””><0.2Every 6-8 hours
MorphineMOUSE5-10Every 4 hours
MorphineRAT5-10Every 4 hours

Acetaminophen (0.1 ml PO of Children’s cherry flavored Tylenol Elixir) at 80 mg/2.5 ml once or twice a day may be acceptable and can be administered using a dropper or TB syringe.1


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