Rodents are often anaesthetised for minor procedures, routine surgery (e.g. castration and ovariohysterectomy) and, from time to time, for more invasive surgery such as a tumour removal
Posted: 26 June 2018
Anaesthesia of rodents follows the same principles as that for dogs, cats and rabbits, though the mortality rate is often higher, mainly as a result of the difficulties associated with;
For most rodents, the safest anesthetics to use are inhalants such as isofluorane and sevofluorane. They’re ideal as they produce rapid onset loss of consciousness with minimal side effects.
Induction of rodents is usually achieved in an induction chamber and requires a precision vaporiser for safe and accurate delivery. It’s also essential to monitor them closely at all times as an overly deep plane of anaesthesia can rapidly lead to fatalities if the concentration is too high.
Two key advantages of these agents is that they’re not metabolised and therefore have little or no toxic effects. They are also relatively insoluble in blood, and therefore easily expelled during respiration ensuring a quick recovery.
Animals under anaesthesia are always at increased risk of hypothermia, and this is particularly so in small rodents. Loss of body heat can be significant especially if they’re clipped and washed to prepare for surgery.
Failure to properly regulate the core temperature can significantly compromise the patient, and can be the difference between the success or failure of a procedure.
In general, smaller animals have higher metabolic rates and frequently require higher doses of anaesthetics and analgesics at more frequent intervals to achieve the desired effect. Monitoring depth of anaesthesia is essential throughout.
This is essential, and is achieved by using all of the following;
Isofluorane is recommended as the first choice of anaesthetic in mice. It should be delivered at a known percentage (1-3% for maintenance; up to 5% for induction) in oxygen from a precision vaporizer.
Surgical anaesthesia can be achieved with the following combination – fentanyl (0.05g/kg) + midazolam (5mg/kg) + medetomidine (0.5mg/kg) given IP
Rat anaesthesia and analgesia considerations are similar to those described for the mouse. Ketamine combinations in mice are more likely to provide adequate surgical anaesthesia and so may not require supplementary isofluorane.
A typical combination for light surgical anaesthesia can include the following – ketamine (75-100mg/kg) + midazolam (4-5mg/kg) both mixed in the same syringe and given IP
Hamster anaesthesia is similar to rat and mouse anaesthesia, though some anaesthetic doses differ.
Guinea pigs can be difficult to anaesthetise so ensure you plan and prepare carefully. They may be anaesthetised by facemask when using isofluorane and sevofluorane. Endotracheal intubation can be attempted, but usually requires specialised training, skill and experience.
Monitoring - the toe-pinch withdrawal reflex is less reliable as an indicator of surgical anaesthesia in this species. The ear pinch response is helpful to monitor depth of anaesthesia.
A typical combination of injectable anaesthesia might include ketamine (40mg/kg) and medetomidine (0.25-0.5mg/kg).
Intraperitoneal administration works well, however avoid the large caecum. Avoid intramuscular injections as they may result in self-mutilation due to irritation. Intravenous injection is difficult.