December 2000

Intravenous Administrations:
Blocked Jugular Vein
by Heather Smith Thomas

Sometimes the intravenous injection of medication or the frequent administration of fluid can cause inflammation of a vein (thrombophlebitis), or blockage of the vein (thrombosis) due to the formation of a clot caused by the irritation. Irritating medications such as phenylbutazone or tetracyclines that slip outside the vein, or a catheter left in place for a long time, are some of the more common things that can cause problems. The blockage is usually not permanent and generally does not pose a serious problem for the horse, but can compromise the vein for a time-so that it cannot be used for giving an I.V. Horsemen are becoming increasingly aware of this problem, and are often concerned about the possibilities of an irritated or blocked jugular vein in horses.

Dr. Terry Gerros, a veterinarian at Santiam Equine Clinic in Salem, Oregon, says "the vast majority of jugular vein thrombosis cases-which are the most common blockages we see in the horse-usually occur from a paravascular (beside the vein) administration of medication, like you would see with bute or some other irritating substance outside the vein. The other very common cause is long-term fluid administration. A horse is sick, suffering from a disease, or he's colicky or has diarrhea and has to be on fluids; he has all these other mediators going around his body (from the primary problem) and then some problems related to the catheter."

Due to the fact that catheters sometimes cause problems, a review of the medical literature on this subject (in both human and veterinary medicine) was done by Gerros in 1991. The information in this report is still of valid interest today.

Intravenous catheters were first used in human medicine in 1945. Some of the serious complications that were soon noticed included septic thrombophlebitis and septicemia, due to bacterial infections introduced by the catheters. Even though the risk for problems in human patients is low (less than 1 percent), the high number of patients requiring catheterization resulted in about 176,000 cases of hospital acquired bacteremia being reported annually (of which about one third are related to intravenous devices), according to the ACVIM review by Dr. Gerros. 

Some of the factors that increase the risk of infection or other complications, include the length of time a catheter is in place, severity of the underlying illness, type of catheter used, improper insertion technique, and inexperience of the person inserting the catheter. These same factors apply to I.V. catheters in horses.

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 polyurethane and nylon, and the veterinarian's choice is based on a number of considerations. These include the cost, bore size, flexibility, ease of administration, length, tendency to kink or bend, length of time it must be left in place, 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.

Softness of the material is an important factor. The softer the catheter, the less the possibility of irritation and clot buildup. The tendency of various plastics to cause irritation was compared in several studies, and the manufacturing process (which affect softness of a plastic) makes more difference than the type of plastic. For instance, silicone rubber, polyvinyl chloride and polyurethane catheters that are comparable in softness are also very similar in thrombogenicity.

The longer a catheter is left in, 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 material that forms a web to catch platelets and create a clot whenever a blood vessel is injured; this is nature's way to create a patch and halt bleeding. But the resultant clot from the constant irritation of a catheter may eventually block the vessel.

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. There is always some movement of the catheter, and it tends to irritate the walls. "The catheter whips in the vein at the end of the fluids," says Gerros. 

"There are precautions that people can take to prevent this, such as altering the type of I.V. catheter that's used, if it has to be left in for very long. The least expensive and most commonly used catheters are made of teflon, and though teflon is a pretty inert substance, it's also more stiff than some others, so when it whips at the end of a vein, it is irritating to the vein. As you run fluid through a catheter, it has a tendency to whip back and forth, so you are better off to use something like polyurethane rather than teflon. The polyurethane catheters are more flexible and less irritating to the vessel," he says.

"The key to minimizing irritation from a catheter, especially if using a teflon catheter, is to leave it in no longer than 72 hours. Most catheters should be changed every 72 hours. There are some long-term catheters; one company makes one that can be in for seven days, and there is also a 30-day catheter, but it's about 15 inches long," says Gerros. Thrombophlebitis (clot formation in the vein, with accompanying inflammation of the vessel wall) is the most commonly reported catheter-related complication in animals.

The signs of this problem can include pain and swelling, as well as a thickened and cordlike vein when examined with the fingers. Jugular thrombophlebitisas due to 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 Dr. Gerros' report. The horse's head may appear swollen on the side that is blocked, due to inability of the blood to return to the heart through the blocked jugular vein. If the blockage is just on one side, the edema may not be severe, and may resolve within a few days as the smaller veins alongside the jugular enlarge to carry the blood flow. But if both jugular veins are blocked, there will be significant swelling around the tongue, pharynx and larynx, which can result in noisy breathing and difficulty in swallowing.

Occasionally a septic thrombophlebitis will develop (in which infection affects the entire body), causing the patient to have a stiff neck and fever, but this is rare in horses. These cases will need medical attention. Most cases are non-spetic, however, and will resolve with time and supportive care.

At the first indication of problems, the catheter should be removed, and the tip cultured for infection. The area can be treated with topical antiinflammatory agents such as DMSO, and in severe cases, nonsteroidal antiinflammatories. Intravenous phenylbutazone should not be used, however, since it can cause severe inflammation of the vessel wall, and create more problems-especially if the horse's blood has an increased tendency to clot.

If the culture shows bacterial infection, the appropriate antibiotic should be used, and given for at least 10 days or until signs of local and systemic sepsis have abated, according to Dr. Gerros' report. Sometimes the septic condition will not resolve until the affected vessel has been removed. If a problem is suspected, then early treatment at the site with an anticoagulant, such as heparin, can help control the extent of clot formation.

As the inflammation resolves, a blocked jugular vein will generally become a firm cord of fibrous tissue. Depending upon the extent of the channel involved and severity of the inflammation, eventually this large vein will often reopen by itself; the blood will tunnel through it. Six months later the vessel may be normal. But use of such a vein for any kind of I.V. 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, or worsen clot formation, or possibly introduce bacteria into a clot, which could result in serious infection.

In discussing medications that end up outside the vein, such as an injection of bute, Gerros says that you can infiltrate the area with saline to dilute any irritating substance that escapes from the vein. "If you are treating your own horse, and you give a shot of bute and get some outside the vein-and you don't realize it until the next day (the area becomes puffy)-you can infiltrate that area with large volumes of subcutaneous isotonic fluids, to dilute it down. If you know it happened when you gave the injection, it's best to do this immediately. This dilutes the concentration of the drug and it's less irritating, and you'll have less problems," he says.

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