Intravenous administration of material can be technically difficult, and use of a restraining device is often required. These should be selected carefully to be an appropriate size for the animal to be injected. Too small a device can result in injuries to the animal, and can interfere with respiratory movements. Too large a restrainer can also result in injury, caused by movements during restraint.
Although rapid buffering by the blood and rapid dilution can allow a wider range of materials to be administered, injection into a peripheral vein can result in irritation, and in some circumstances flushing with normal saline should be considered.
It is common practice to stimulate dilation of the tail veins in mice either by placing them in a warmer environment (e.g. at 28-30 ºC) for up to 30 minutes, or by placing the tail in warm (30-35 ºC) water. If a warming box or incubator is used, its temperature should be monitored carefully. It is good practice to place an electronic thermometer adjacent to the animal’s cage in the incubator, as the temperature registered by the device thermostat may not be accurate.