Radial Vein Blood Collection in the Miniature Pig

Introduction

Blood collection in the conscious miniature pig can be a challenge. Peripheral veins are not readily accessible and some vessels, such as the auricular vein, are inadequate for obtaining sufficient volume from some individuals. The cephalic vein is also difficult to access, often requiring a cutdown through the overlying thick skin in adult pigs. Additionally, collection from the more commonly used jugular vein in a conscious animal can be associated with complications, such as hematoma formation, thyroid gland damage, or even the occasional death. The stress induced by restraint required for jugular vein access can also be problematic.

The radial vein is located along the medial aspect of the forelimb. This vessel is relatively straight and generally superficial (Fig 1).

Dissection of a porcine forelimb illustrating superficial veins and landmarks. Credit: Dr. James E. Smallwood

Figure 1. Dissection of a porcine forelimb showing the superficial veins and landmarks: (1) cephalic vein (2) accessory cephalic vein (3) radial vein (4) location of accessory carpal bones (palpable). The needle indicates the site for venipuncture as the radial vein crosses the flexor retinaculum of the carpus. Diagram credit: Dr. James E. Smallwood. Click image to enlarge

Radial vein blood collection can be successfully employed in pet mini pigs without complications and with minimal stress, particularly when a food distraction is offered. Use of a sling can facilitate blood collection if the pig is acclimated to the device, as the animal cannot see the technician and can be distracted with food treats (Fig 2). Often the pig has no reaction to needle insertion or manipulation of the limb. The vein is also easily accessed when the animal is placed in dorsal recumbency, such as in a V-trough. (Although, of course, a food distraction should not be attempted when the animal is on its back).

Figure 2. A miniature pig patient in a sling. The Panepinto sling is an excellent means of restraint and is primarily marketed for use in research pigs. Unfortunately, expense ($4000-$5000) makes the sling impractical for most clinics. Photo credit: Dr. Kristie Mozzachio. Click image to enlarge

Method

  1. Restrain the animal and apply pressure to the medial aspect of the proximal forelimb, near the axillary region, to occlude the vein (Fig 3 red arrow).

    Medial aspect of the forelimb of a miniature pig. The curved red line delineates the carpal glands, which often bear visible brown discharge. The red circle identifies the accessory carpal bone. The groove that lies along the radius/ulna is faintly visible as a depression between bone & musculature.

    Figure 3. Medial aspect of the forelimb of a miniature pig. The curved red line delineates the carpal glands, which often bear visible brown discharge. The red circle identifies the accessory carpal bone. The groove that lies along the radius/ulna is faintly visible as a depression between bone & musculature. Photo credit: Dr. Kristie Mozzachio. Click image to enlarge.

  2. The phlebotomist grasps and stretches out the limb, with a thumb on the caudal aspect of the leg.
  3. Palpate the caudal edge of the antebrachium and the small, rounded accessory carpal bone along the caudal aspect of the limb (Fig 3 red circle), which can be felt as a little “lump” just above the dew claws. The radial vein lies in a groove between these two landmarks (Fig 1). The vein is sometimes visible in young or light-colored animals, but more commonly the vein is neither visible nor palpable.
  4. Insert a 1-inch 22-gauge needle parallel to the long bone (Fig 4). Rapid clotting can create difficulty with smaller gauge needles.

    Blood is collected from the radial vein of a miniature pig. The needle is inserted along the groove, parallel to the radius and ulna. The most distal part of the vein lies in the region of the carpal glands which appear as a dark brown smudge on the skin just distal to needle insertion point in the image. Note: Since this pig is white-skinned and fairly young, the vein under the skin is visible, but this very uncommon.

    Figure 4. Blood is collected from the radial vein of a miniature pig. The needle is inserted along the groove, parallel to the radius and ulna. The most distal part of the vein lies in the region of the carpal glands which appear as a dark brown smudge on the skin just distal to the needle insertion point in this image. Note: Since this pig is white-skinned and fairly young, the vein under the skin is visible, but this very uncommon. Photo credit: Dr. Kristie Mozzachio. Click image to enlarge.

  5. Apply gentle, steady negative pressure to obtain the desired volume. The radial vein is large enough to facilitate collection of a significant volume of blood (e.g. 3-6 ml). Apply only a small amount of suction, particularly if a larger syringe (i.e. 6 ml) is used to prevent collapse of the vessel.
  6. “Pumping” or slowly applying and releasing pressure at the site of occlusion can aid sampling.

It is not known whether the radial vein lends itself to the repeated collections required by some research protocols, but the vessels extends along the length of the limb. If the initial sample is taken distally, subsequent samples can theoretically be taken at progressively more proximal points.

 

Summary

The radial vein, located along the medial aspect of the forelimb, is readily available for blood sampling in the miniature pig. The radial vein provides easy and safe peripheral venous access.

 

References and further reading