Diving and Blood Thinners

By Fred Bove, M.D., Ph.D.

We have received a number of inquiries recently about divers who take the anticoagulant Coumadin.

Although the ability of the blood to clot is one of the most important defenses against blood loss when injured, there are certain conditions where reducing the ability to clot is beneficial. Coumadin is used when there is a risk of blood clotting owing to illness, artificial heart valves, certain abnormal heart rhythms or disease of the veins (phlebitis). Coumadin causes the blood to clot more slowly, thereby protecting the person from clots that may form in the veins or in the heart and travel to vital organs to cause damage and abnormal function.

There are many thousands of people taking Coumadin. All must have a blood test periodically (usually monthly) to determine that the level of anticoagulation is proper and undergo an initial period of adjustment where tests are done every few days or weeks. Decisions about the proper amount of the medication are made by a physician who must monitor clotting time and adjust the dose accordingly. The physician uses the International Normalized Ratio (INR). This compares the clotting time of an individual’s blood to a standard. The normal ratio is one. Ratios of 2 to 2.5 are used in some cases of vein disease or abnormal heart rhythms, while in the case of heart valves, the ratio is maintained at 2.5 to 3.5 to minimize risk of clotting. People taking Coumadin get into a routine of getting a blood test once a month and checking with their physician to determine if the Coumadin dosage should be changed.

Coumadin reduces the ability of the blood to clot by blocking the effects of vitamin K. This vitamin is important in producing one of the factors (prothrombin) needed for blood to clot. Clotting requires a large number of chemical interactions in the blood. The absence of any one of the required factors will reduce the ability of the blood to clot. By lowering the amount of prothrombin, clotting is prolonged. Vitamin K requires activity of bacteria in the intestine; certain antibiotics can cause a reduction in bacterial activity, loss of production of vitamin K and an increase in the effects of Coumadin. When the blood is too thin, spontaneous bleeding occurs. This is often first noticed in the mouth or in the intestines.

Drugs, illness or dietary change can affect the level of blood clotting when taking Coumadin. Physicians and pharmacists should be aware of drug interactions and avoid or adjust for medications that can alter clotting time. Education about dietary effects is important. Aspirin should be avoided when taking Coumadin because it blocks the platelet clotting mechanism and leaves no protection against bleeding.

Divers who must take Coumadin have a risk of bleeding from injury, ear and sinus squeeze and pulmonary barotrauma. Since the blood clots more slowly, a cut will bleed longer and may require compression bandages. An ear or sinus squeeze will cause excess bleeding if it is severe enough to cause damage to blood vessels in the middle ear or in the sinuses.

In spite of the risk of bleeding, many otherwise healthy people get along for many years using blood thinners and have minimal complications. Contact sports are discouraged because of the risk of injury but many other sport and recreational activities, including diving, can be done safely with carefully monitored blood clotting time. We have encountered divers with artificial heart valves who are diving safely, individuals with atrial fibrillation; an abnormal heart rhythm; who dive safely and a few divers who had phlebitis (clotting in the veins) who take Coumadin and dive without incident.

The secret of safe use of Coumadin is careful attention to the INR, with monthly blood tests and continued surveillance by the physician. With good control of blood thinning, the risk of complication is quite low.

For divers, the most important question is whether the condition that requires the use of Coumadin prohibits diving. In many cases, the illness is over, or chronic but well adjusted, and does not interfere with safe recreational diving. Safe diving with Coumadin depends on the absence of illness that would limit diving, careful control of clotting time, avoiding ear or sinus squeeze and a thorough education on drugs and foods that cause changes in the effects of Coumadin. There are many divers using Coumadin safely, but a special effort must be made to understand how to avoid problems of excess or not enough.