Administering injectable anaesthetics for surgical or prolonged procedures

Administration route choices

• Intramuscular (IM) – It takes about 5-10 minutes for anaesthesia to develop after intramuscular administration. Can cause pain on administration in small rodents as the muscle mass is so small relative to the volume to be injected. Some agents are irritant and can cause muscle damage (e.g. Ketamine).
• Intravenous (IV) – Ideal as the dose can be adjusted to be appropriate for the individual animal, and to produce the depth of anaesthesia required. Unfortunately intravenous injection is technically demanding in small rodents.
• Intraperitoneal (IP) – This is one of the most widely used means of giving injectable anaesthetics to rodents, but in 5-10% of cases not all of the injected anaesthetic is delivered intraperitoneally (Steward et al, 1968, Gaines Das and North, 2007). If a large proportion is delivered into the fat or intestines, then an inadequate anaesthetic effect will be produced. Not all anaesthetics are suitable for administration by this route
• Subcutaneous (SC) – It takes 5 – 15 minutes for anaesthesia to develop after subcutaneous administration. It may be less stressful and produce more consistent results than use of the intramuscular or intraperitoneal routes. Not all anaesthetics are suitable for administration by this route.