Porcine Clinical Procedures

Porcine Clinical Procedures

Diagnostic Sampling

All diagnostic procedures performed in other species, such as abdominocentesis, arthrocentesis, and transtracheal wash, can be performed in swine. Due to economic costs associated with some of these tests and the cost of treating serious medical diseases when they occur, these and nonroutine diagnostic tests more likely will be pursued for valuable breeding stock than for production animals. However, routine diagnostic tests such as blood sampling are commonly performed in swine for disease screening.

Venous Blood Sampling

Blood is the material most commonly collected for testing in swine. Swine red blood cells are somewhat fragile; therefore, using appropriately sized needles and avoiding aspiration or injection of blood through needles with unnecessary force are important. Sites of blood collection should always be cleaned before needle insertion.

Several veins are accessible for blood sampling. The site and technique for venipuncture depend on the size of the pig and the method of restraint. The following locations are accessible.

Lateral Auricular Vein

The “ear” vein is useful for obtaining small samples of venous blood (<5 ml). It is used for pigs after weaning age (4–5 weeks old, 25-lb body weight). A 20-gauge (ga) × 1-inch needle is suitable for most animals. An 18- to 20-ga × 1-inch needle can be used in large adults. Butterfly catheters may be useful. Vacutainers are not recommended at this location because they tend to collapse the vein, especially in small individuals.

The vein runs near the lateral border of the ear pinna and is accessed from the dorsal (haired) side of the pinna (Figs. 23-1 and 23-2). It is easily visualized and can be distended with finger pressure at the base of the lateral surface of the ear, although both hands of the technician can be freed up by using a mechanical method to distend the vein. A rubber band can be placed as a tourniquet around the base of the ear to distend the vein. Another method uses self-retaining forceps with long, plastic-covered jaws that are placed across the base of the ear to distend the ear vein. This method leaves one hand free to stabilize the tip of the ear while the other hand places the needle and aspirates the blood. The needle should enter the vein at a 45-degree angle to the skin. The ear vein may continue to bleed for several minutes after venipuncture is completed.

Cranial Vena Cava

The cranial vena cava lies in the thoracic inlet between the first pair of ribs and gives rise to both the right and left jugular veins. Although learning to draw blood from this location is technically more difficult, this location is the most satisfactory for obtaining large blood samples and is suitable for any size animal. The right side of the animal is always used to access the cranial vena cava, to avoid accidental damage to the phrenic nerve. The left phrenic nerve lies in a more vulnerable position, paralleling the left external jugular vein, than does the right phrenic nerve, which is more protected on the right side of the animal. In piglets, a 20-ga × image-inch needle can be used. Small pigs up to 50 lb require an 18- to 20-ga × 1- to image-inch needle. Small pigs are placed in dorsal recumbency with the head held firmly still. The front legs are extended and pulled caudally for complete access to the caudal neck and shoulder area. The needle is inserted (syringe attached) on the right side, at the caudal extent of the right jugular furrow, just lateral to the manubrium of the sternum. The needle is directed toward the caudal aspect of the top of the opposite (left) shoulder blade. Slight backpressure (vacuum) is kept on the syringe. The vena cava is encountered at a depth between image and 2 inches, depending on the size of the animal. Blood is easily aspirated when the needle enters the vein.

Larger animals are restrained while they are standing, usually with a hog snare. The head should be raised slightly. Alternatively, some farms use a bleeding chute with a head catch. Nonslip footing should be provided. If the pig sits down before or during the procedure, stop the procedure, withdraw the needle, and get the pig on all four feet. Sitting alters the anatomical landmarks for the procedure and makes it difficult to perform successfully. An 18- to 20-ga × image-inch needle is used for feeder (finisher) pigs weighing more than 50 lb. In adult swine, a 16- to 17-ga × 4- to image-inch needle is needed. The syringe is attached for the procedure. The technician kneels in front of the animal on the right side (facing the body of the pig) or to the side of the right shoulder (facing the neck). The needle is inserted and directed exactly as described earlier (Figs. 23-3 and 23-4). Once the skin has been penetrated, slight backpressure is maintained on the syringe plunger. Blood flows readily when the vein is entered. In adult pigs the vein lies quite deep, up to 4 inches.

Several structures may be encountered accidentally during this procedure. If the needle hits a rib, pull backward slightly and try a different angle. If the needle penetrates the trachea, the syringe fills with air. If the needle enters the thoracic duct, the syringe fills with lymph. Punctures of the trachea and thoracic duct rarely are life threatening; when encountered, they indicate that the needle is angled too far medially. The right vagus nerve, if hit, can damage the function of the parasympathetic nerves to the heart. The right phrenic nerve, if hit, can alter the function of the diaphragm. Cardiac and/or respiratory signs may follow and require emergency treatment.

Jugular Vein

Because the jugular vein is not as deep a structure as the cranial vena cava, it is a safer structure for access with a needle. However, the jugular veins are not as large in diameter and may be difficult to find and hit, especially in large or heavy animals. The jugular vein can be used for sampling animals of any age. Needle size ranges from 20 ga × image inches in piglets to 16 ga × 3 to image inches in mature pigs.

The right jugular vein is preferred, to avoid damaging the phrenic nerve. The jugular vein lies in the jugular furrow and is accessed cranially to the manubrium at the visually deepest point of the jugular furrow. The vein is not distended; this is a blind stick procedure. The needle (with syringe or vacuum attached) is inserted perpendicular to the skin and directed dorsocaudally and slightly medially. After the skin has been penetrated, slight backpressure should be kept on the syringe.

Orbital Sinus (Medial Canthus of the Eye)

The venous sinus is located adjacent to the medial canthus of the eye and can be used for venous blood collections in pigs of any age. Approximately 5 to 10 ml of blood can be obtained. Small pigs are restrained in dorsal recumbency, inclined with the head down, and firmly restrained. Larger pigs are restrained standing with a hog snare. Piglets require a 20- to 20-ga × 1-inch needle. Larger pigs require a 16- to 20-ga × image-inch needle. The needle is inserted deep to the nictitating membrane (third eyelid) and advanced at a 45-degree angle toward the opposite jaw. The needle will hit the lacrimal bone. Rotate and slightly withdraw the needle until blood flows from the hub. The needle is then attached. Aspiration should be gentle (Fig. 23-5).

Cephalic Vein

The cephalic vein is accessible in small pigs older than 14 weeks but is not commonly used. It runs along the cranial–medial surface of the upper forelimb. The pig is restrained by snout restraint in the standing position. The leg is not lifted off the ground. Distension of the vein is similar to that in small animals and can be achieved by hand or tourniquet. The needle is placed at a 45-degree angle to the skin, in a proximal direction. A 20-ga × 1- to image-inch needle is sufficient. Up to 10 ml of blood can be obtained.

Normal complete blood count and blood chemistry values for swine are listed in Tables 23-1 and 23-2, respectively.

Aug 11, 2016 | Posted by in INTERNAL MEDICINE | Comments Off on Porcine Clinical Procedures

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