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Rat : Temporary cannula (non-surgical) *updated
Temporary cannulation of the lateral tail vein should be considered when repeated blood samples are required over a short period of time (e.g. a few hours) as it avoids multiple needle entries without repeat damage to the tail vein. The technique may be combined with normal tail vein bleeding to accommodate all the blood samples required by a given protocol but reduce the number of needle entries and reduce the time the rat must spend in a warming cabinet (since warming may not be necesary for taking blood via the temporary cannula). It is suitable for use in all strains of rats, and the animals can be group-housed during the study period.
Tail bleeding normally requires the rats to be
warmed in order to dilate the blood vessel prior to
taking the sample. This may be stressful and can cause
dehydration due to salivation, in addition to
increasing metabolic rate, which may affect the
experimental data. Restraining the rat for long periods of time
in a restraint tube may also cause it to become hot, which will
be stressful to the rat and may affect the blood parameters.
View this technique below.
No surgery is required. An intravenous catheter is inserted into the vein by puncture of the skin and taped in situ . A heparin flush is used (0.1 ml) after placement and between samples to prevent clotting. An access port is inserted into the exteriorised end of the cannula, which stops the blood from flowing, and the catheter is taped into place.
Aseptic technique should be used. A local anaesthetic cream (e.g. EMLA cream) can be applied to the site 30 minutes prior to insertion of the catheter. The tail may need to be washed with diluted Hibiscrub (1%) in order to see the blood vessel.
0.1 - 2.0 ml (normally 0.1 - 0.3 ml) can be taken per sample, and depending on the sample volume and consideration of the effects of repeated warming and restraint, no more than six samples in a 2-hour period or eight samples in a 24-hour period.
The lateral tail vein is usually accessed approximately one-third along the length of the tail from the tail tip. Cannulation should not be attempted at the base of the tail, as this could result in a perivascular clot and inflammation that significantly reduces blood flow to the distal portion of the vessel. If cannulation is unsuccessful, direct venepuncture may be used as the alternative. The number of attempts to take any blood sample should be minimised (no more than three needle sticks in any one attempt).
A warming cabinet is used prior to the cannulation (39oC for 5 to 15 minutes). Subsequent warming prior to sampling may not be required so long as blood is 'free flowing'. If necessary, the rat can be warmed for a short period (5 minutes) as required. The rat should be carefully monitored, including checking for signs of hyperthermia and dehydration. The time the rat is in the warming cabinet should be recorded and the cabinet should be calibrated regularly to avoid hyperthermia; digital displays should not be relied upon. It is important to ensure the temperature in the cabinet is uniform and that there are no 'hot spots'. Alternatively, a warm bath at a maximum of 40oC can be used to warm just the tail of the rat. The temperature of the bath should be monitored otherwise the tail can be scalded.
Rats need to be restrained which can cause stress and therefore the duration of restraint should be minimised. Restraint can either be manual (e.g. wrapping the rat in a towel) or using a restraint tube. Anecdotal evidence suggests that holding the rat is less stressful than using a restraint tube. Where a restraint tube is used, it should be appropriate to the size of the rat in order to avoid damage to the tail, testes, limbs and back. All forms of restraining equipment should be frequently washed to prevent pheromonally-induced stress or cross-infection.
Number of samples:
Ideally, no more than six samples in a 2-hour period, or eight samples in a 24-hour period, depending on sample volume and consideration of the effects of repeated warming and restraint.
0.1 - 2.0 ml (normally 0.1 - 0.3 ml)
22G 0.90 mm i.v. catheter
One person is required to take the blood sample if a tube restrainer is used. For large batches of animals, two people are required: one person to take the blood sample and one to operate the warming cabinet.
Rats are warmed to dilate the blood vessel and care should be taken to avoid hyperthermia and dehydration. The time the animal is exposed to warming and restraint should be minimised.
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