Blood Thinners & Diving

Blood thinners are the common name of a number of groups of drugs and chemical substances that can prevent or reduce the coagulation of blood. These drugs can be prescribed to treat a number of blood diseases and to prevent some complications derived from normal clotting, but blood thinning can also be an unintended side effect of some drugs. The biggest risk of blood thinners is excessive or uncontrolled bleeding, which, in a diving environment, could turn into a challenging medical emergency.

What is a clot?

Clots form when blood cells known as platelets stick together, and then proteins in the blood bind them together into a solid mass. This solid mass of blood is called a clot, and when the clot forms inside a blood vessel, it is called a thrombus.

Clotting is a normal function that limits and stops bleeding when a blood vessel is injured. However, if a clot grows out of control or starts to travel within the circulatory system, it then poses a danger. Clots may get lodged in a pulmonary artery and cause a pulmonary embolism; in the arteries of the heart and cause a heart attack; or in the vessels of the brain and cause a stroke. All of these events can be life-threatening.

What are anticoagulants used for?

Anticoagulants and antiplatelets are two classes of drugs that reduce the risk of clot formation. These drugs are usually prescribed to reduce the risk of deep vein thrombosis (DVT), pulmonary embolism (PE), heart attack, and stroke. They may also be prescribed for individuals who have been diagnosed with atrial fibrillation or for those who have had heart-valve surgery or who have received a stent, an implanted pacemaker or an implanted defibrillator. Other patients may require these drugs to counteract an inherited disorder (like Factor V Leiden deficiency or thrombophilia) or an acquired hypercoagulable state like deep vein thrombosis (DVT) or pulmonary embolism due to a recent trauma or surgery, cancer, obesity, pregnancy and others.

Antiplatelets and anticoagulants keep blood from clotting as quickly or as effectively as usual by preventing the platelets from adhering to one another and by preventing the clotting proteins from binding together. They can even help to break up clots that have already formed.

  • Antiplatelets — Drugs such as aspirin and clopidogrel (also known by the brand name Plavix) work by preventing the platelets from adhering to one another.
  • Anticoagulants — Heparin, warfarin (also known by the brand name Coumadin) and other similar drugs inhibit the action of the clotting proteins and thus slow down the chemical reactions that lead to the formation of a clot. There are also several newer anticoagulants, including rivaroxaban (Xarelto), dabigatran (Pradaxa), and apixaban (Eliquis).

The major side effect of all antiplatelets and anticoagulants is excessive bleeding. Those taking such drugs — especially at too high a dosage — may bleed or bruise easily or may experience bleeding that does not stop as quickly as usual.

Implications in Diving

Individuals who take warfarin (Coumadin) are generally advised to avoid any activities that may cause abrasions, bruising or cuts — such as contact sports. They are also urged to exercise caution while brushing their teeth and shaving. Even such trivial injuries as insect bites may cause complications in anyone taking warfarin.

There are additional risks involving warfarin, particular to diving. Most significantly, there is an appreciable chance of serious injury in any diving environment, despite one’s best efforts to mitigate the risk. Cuts and bruises are unavoidable, for example. And for anyone taking warfarin, a decompression injury or difficulty equalizing ear pressure could cause bleeding in the ears or the spinal cord that would otherwise not occur. In addition, both travel and any resulting dietary disruption can interfere with the action of warfarin in dangerous ways. Furthermore, the health-care capabilities in many popular dive destinations may not be up to providing the care that would be required in case of an adverse event. For all these reasons, anyone taking warfarin is generally advised not to dive. Nevertheless, many people who take warfarin are able to dive without major complications. The keys to safe diving while using warfarin are strict adherence to monthly blood tests and regular surveillance by a physician. With good control of blood-thinning, the risk of a bleeding complication is quite low.

Increased Risks in Diving

  • Cuts and bruises are common injuries in almost any recreational outdoor activities. Under normal circumstances, these injuries can be effectively and efficiently managed on-site with proper first aid techniques. However, proper first aid bleeding control techniques may be ineffective on someone who is taking anticoagulants. Under these circumstances, minor injuries can easily become a true medical emergency.
  • Middle-ear or sinus barotraumas are by far the most common diving injury, accounting for almost 40 percent of the calls received on the DAN Emergency Line. Under normal circumstances, these injuries are self-limited, as normal coagulation stops the internal bleeding. This allowing the injured diver some time to seek professional medical evaluation for assessment and treatment. When a diver is under anticoagulants, bleeding can only be controlled by applying pressure to the wound, which is not possible on internal bleedings. Under these circumstances, ordinary ear, nose and throat (ENT) barotraumas can easily become a true medical emergency.
  • Decompression illness (DCI) takes the risk of bleeding to a new dimension. Bubble formation and growth are known to cause microscopic tissue damage, both through mechanical tissue disruption as well as through normal inflammatory processes. Under normal circumstances, coagulation can control these micro bleeding, and recompression therapy can revert bubble growth, wash-out inert gas, and minimize the inflammatory effects of the injury. When a diver is under anticoagulants, the micro bleeding caused by bubbles can reduce the effectiveness of recompression therapy. This is particularly important in severe DCI cases, like when there is spinal cord involvement or an arterial gas embolism.
  • Watch your diet. People taking oral anticoagulants derived from coumarins (like warfarin, acenocoumarol, phenprocoumon, atromentin and phenindione) usually have some dietary restrictions, as an excess in vitamin K in the diet can lessen the effectiveness of the anticoagulant. Foods that are rich in vitamin K include leafy greens like kale, spinach, Brussels sprouts, broccoli, asparagus, collards, mustard greens, Swiss chard and green tea. Small amounts of these vitamin-k-rich foods shouldn’t cause a problem, but large amounts or small amounts over several days could alter the desired balance of anticoagulation therapy prescribed. On the other hand, alcohol and drinks like cranberry juice can increase the anticoagulant effect of these drugs.
  • Gastrointestinal maladies (traveler’s diarrhea, changes in diet, vomiting, etc.) are important considerations and can also have a negative impact on the delicate balance of homeostasis by altering the bioavailability of the drug, the absorption and availability of vitamin K, or both.