What would happen to your horse if both of his jugular veins were damaged so that they were off-limits for taking blood for testing or administering medications and hampered the drainage of blood from his head? Sometimes an intravenous (IV) injection of medication or administration of fluid can cause inflammation of a vein (thrombophlebitis) or blockage of the vein (thrombosis) due to the formation of a blood clot. Irritating medications (such as phenylbutazone and tetracyclines) that slip outside the vein or a catheter left in place for too long are some of the more common things that can cause problems in veins. For a number of years, horsemen have become increasingly aware and concerned about the possibility and repercussions of an irritated or blocked jugular vein in a horse.

Because catheters can cause problems in veins, a review of the medical literature on this subject (in both human and veterinary medicine) was done in 1991 by Terry C. Gerros, DVM, a veterinarian now in practice at Santiam Equine in Salem, Ore.1 That information is still valid for horsemen and veterinarians today.

Intravenous catheters were first used in human medicine in 1945. Some of the serious complications that were soon noticed included septic thrombophlebitis (an infected vein with a blood clot) and bacteremia (bacteria in the circulating blood) due to bacterial infections introduced by the catheters. Although the risk for problems in human patients even 20 years ago was low (less than 1%), the high number of patients requiring catheterization resulted in about 176,000 cases of hospital-acquired bacteremia reported annually (of which about one-third were related to intravenous devices), according to the review by Gerros.

Some of the factors that increased the risk of infection or other complications included the length of time a catheter was in place, severity of the underlying illness, the type of catheter used, improper insertion technique, and inexperience of the person inserting the catheter.

In another study examining horses, fever, diarrhea, and use of homemade intravenous fluids were all associated with an increased risk of jugular vein thrombosis. Length of catheter use in horses was also considered a prominent risk.2 These same factors apply to IV catheters in horses.

Types of Catheters and Problems

The type of catheter (material from which it is made) plays an important role in clot formation. There are several kinds of plastic catheters, including silicone, polyethylene, polyurethane, and nylon. The veterinarian's choice is based on a number of considerations, including cost, bore size, flexibility, ease of administration, length, tendency to kink or bend, the length of time it must be left in the vein, as well as thrombogenicity (how much irritation it might cause, which would contribute to clot formation). Silicone rubber catheters are less irritating than most others, as shown by their ability to be left in for more than 30 days with only minor complications.

The reaction of the vein and blood to the material is an important factor. Usually the softer catheters cause less physical irritation and clot buildup. The tendency of various plastics to cause irritation has been compared in several studies. For instance, silicone rubber, polyvinyl chloride, and polyurethane catheters with comparable softness are also very similar in thrombogenicity (low tendency to cause a thrombus, or blood clot anchored within a blood vessel).

The longer a catheter is left in the vein, the greater the chance for clot formation, unless the catheter is made of a very soft material. The stiffer catheters, such as those made from nylon or polyethylene, tend to rub against the vessel wall along most of their length. This causes fibrin to build up on the catheter as well as creating inflammation of the vein. Fibrin is the sticky protein that when combined with platelets forms a clot whenever a blood vessel is injured; this is nature's way of creating a patch and halting bleeding. But the resultant clot from the constant irritation of the catheter can eventually block the vessel.

Thrombophlebitis is the most common catheter-related complication in animals. Some degree of clot formation will occur around any indwelling catheter regardless of the material due to damage to the vein at the point of insertion and at the site where the catheter touches the vessel wall.

Jugular thrombophlebitis due to irritation from a catheter is especially common in horses suffering from severe gastrointestinal tract diseases that are accompanied by endotoxemia (such as acute toxic colic, enteritis, and intestinal strangulation obstruction), according to Gerros' report. The more reactive the catheter material or the greater the exposure of the horse to shock or endotoxemia, the more likely the thrombophlebitis can cause a serious complication.

Signs of thrombophlebitis can include pain, swelling, and a thickened vein that feels cord-like. If the blockage is just on one side, edema is not usually seen in the head. But if both jugular veins are partially or completely blocked, there will be swelling of the face, muzzle and potentially of the membranes in the nostrils, pharynx, and larynx, which can result in noisy or difficult breathing and difficulty in swallowing.

Thrombophlebitis can be local or cause systemic signs, causing the patient to have a swollen neck and fever. These cases need immediate medical attention. Most cases are non-septic, however, and will resolve with time and supportive care.


At the first indication of a problem, the catheter should be removed and the tip cultured to check for infection. The area where the jugular was affected can be treated with topical anti-inflammatory agents such as dimethyl sulfoxide (DMSO), and in severe cases, systemic treatment with non-steroidal anti-inflammatory drugs such as Banamine might be needed. Use of hot packs appears to reduce edema, and anticoagulants such as heparin might keep the thrombus from growing in size.

If the culture shows bacterial infection, the appropriate antibiotic should be used until signs of local and systemic sepsis have abated, according to Gerros' report. In cases of severe septic thrombophlebitis, the condition might not resolve until the affected portion of the vessel has been removed. Because the normal ends of the vein can't be connected to each other after removing a large segment of diseased vein, these horses will have only one jugular vein. One jugular vein allows for normal drainage of blood from the head, but often alternate veins are chosen in these cases if medical treatment requires frequent IV administration of drugs.

A blocked jugular vein will generally become a firm cord of fibrous tissue as the inflammation resolves. Depending upon the length of the vessel that's affected and severity of the inflammation, this large vein will often reopen itself eventually; the blood will tunnel through it. Six months later the vessel might be normal. But use of such a vein for any kind of IV injection should be avoided while there is any degree of thickening. This type of irritation (puncture of the vein) in a region of resolving inflammation could start the problem all over again, worsen clot formation, or possibly introduce bacteria into a clot, which could result in serious infection.

Any horse with an indwelling IV catheter should be monitored closely for the swelling and/or thick, rope-like consistency of a vein with thrombosis or thrombophlebitis. Catching any vein problem early and treating it minimizes the risk of serious problems.



1 Gerros, T. Intravenous Catheter Complications. ACVIM Review, 1991.

2 Traub-Dargatz, JL; Dargatz, DA. A retrospective study of vein thrombosis in horses treated with intravenous fluids in a veterinary teaching hospital. Journal of Veterinary Internal Medicine, 8(4), 264-266, 1994.

About the Author

Heather Smith Thomas

Heather Smith Thomas ranches with her husband near Salmon, Idaho, raising cattle and a few horses. She has a B.A. in English and history from University of Puget Sound (1966). She has raised and trained horses for 50 years, and has been writing freelance articles and books nearly that long, publishing 20 books and more than 9,000 articles for horse and livestock publications. Some of her books include Understanding Equine Hoof Care, The Horse Conformation Handbook, Care and Management of Horses, Storey's Guide to Raising Horses and Storey's Guide to Training Horses. Besides having her own blog, www.heathersmiththomas.blogspot.com, she writes a biweekly blog at http://insidestorey.blogspot.com that comes out on Tuesdays.

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