Saphenous cannulation

Please read the general principles of blood sampling page before attempting any blood sampling procedure.

For more information on cannula choice and maintenance, please refer to our vascular catheters pages.

Technique

Cannulation of the saphenous veins of pigs is suitable for repeat sampling of small volumes (<2 ml). The technique can be used as an alternative to repeat sampling of the ear veins of minipigs which are small and can collapse if too much vacuum is applied when withdrawing the sample. Cannulation can also be used to administer as well as withdraw fluids.

The pig needs to be restrained for sampling and this can be stressful. Stress can be minimised by training the animal to cooperate with the procedure and by conducting it in a quiet environment. Pigs are intelligent animals and will remember receiving a reward (e.g. food treat) after the procedure, which can make them easier to handle on subsequent occasions. Positive reinforcement training should be used where possible for all procedures from weighing to procedural work to minimise stress to technician and pig.

For cannulation surgery, pigs need to be anaesthetized. Fasting of the pig is required before anaesthesia, and removal of the bedding overnight is recommended as pigs may consume bedding if hungry. To provide warmth to compensate for the removal of the bedding, heat lamps may be provided. Stress can be minimised by training the animal to accept the anaesthetic mask or face cone (and any restraint or lifting).

This technique should be carried out aseptically, with the hind legs clipped and cleaned around the area to be cannulated. The hind legs should be warmed in order to dilate the vessel. A glove filled with warm water and tied off can be used as a simple means to dilate the vessel. A tourniquet can also be used also to help dilate the vessel.

A VeinViewer® or similar product may also be used. This piece of equipment uses near-infrared light (which is absorbed by blood and reflected by surrounding tissue) to show the position of the veins to aid good placement of the cannula. (Note this tool is only useful for shallow veins as the light it emits has penetration depth of 1.5mm).

The vein is occluded below the area of insertion of the cannula. A small incision is made with a scalpel above the vein, this aids in placing of the cannula as pig skin is very tough and the cannula can be damaged (kinked) without this. The cannula is slid up the vein until blood is seen within the cannula. At this point, the guide needle should be withdrawn carefully and the cannula can then be positioned in the vessel without damaging it. The cannula is then capped and 200µl of lock solution (e.g. heparin) administered into the cannula to maintain patency. The cannula can then be secured in place with adhesive tape. The pig can then be recovered in home pen or sling. 

All subsequent blood samples can be taken from the cannula, and patency maintained with the administration of locking solution each time a sample is taken. Pigs can be trained to sit in slings for sampling or gently restrained. The cannula should be checked after sampling before the animal is returned to its pen and during routine checks.

Multiple samples may be collected, taking into account project licence and sample volume limits. 

Summary

Number of samples

Multiple in any 24-hour period.

Sample volume

1 - 3 ml, depending on the size of the pig.

Equipment

18G cannula, adhesive tape, cannula cap, locking solution (e.g. heparin).

Staff resource

Resource requirements will vary depending on the size of the animal and the amount of training and handling received. A minimum of two people will be needed to restrain the pig, anaesthetize, cannulate and take the blood sample. 

Adverse effects

  • Bruising
  • Haemorrhage
  • Infection
  • Cannula failure

Other

Pigs should be trained to cooperate with blood sampling in order to minimise stress. A reward (e.g. food treat) should be given, where possible, after the procedure.

Resources and references

Temporary Saphenous cannulation sampling in other animals

This technique is only appropriate for use in the pig.

All blood sampling techniques in the pig

Click here for information on ear vein sampling in the pigClick here for information on cranial vena cava sampling in the pig