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Diving Medicine

Pulmonary Embolism and Blood Thinners


By Dr. David Sawatzky

In DIVER September 2002 I talked about blood thinners and diving, a discussion about deep venous thrombosis (DVT) and the requirement for people diagnosed with a DVT to be on a blood thinner for several months afterwards.  To be clear, ‘blood thinners’ do not actually thin the blood.  They interfere with the clotting mechanisms so that the blood clots less easily than normal.  This is a mixed blessing. Blood must clot whenever we cut ourselves or damage the blood vessels in any way. The bottom line is that you should not dive while taking a blood thinner because of the increased risk of bleeding.  After you are off the blood thinner it should be safe to return to diving.

A short while ago I received a call from a diving instructor who’d been diagnosed with a pulmonary embolism (PE) last summer and who’d then taken blood thinners for six months and was now off them.  He wanted to know if it was safe to return to diving.  In this column I’ll review pulmonary embolism and the concerns of diving afterwards.

PE Common

Pulmonary embolism is relatively common (one per 1,000 people per year in the USA) and is the second most common cause of sudden death, after cardiac problems.  It’s the third most common cause of death in hospitalized patients (approximately 650,000 cases annually in the USA) and is present in 60 per cent of people who died while in hospital (the diagnosis was not made prior to death in many cases).  If someone dies ‘unexpectedly’ while in hospital, massive PE is seen on 80 per cent of the autopsies.

Pulmonary embolism is 50 per cent more common in blacks than whites and 50 per cent more common in whites than in Asians, Pacific Islanders and American Indians.  Before age 50 PE is slightly more common in women and after age 50 PE is slightly more common in men.  PE is more common in people who sit a lot, and it may account for 15 per cent of postoperative deaths, especially after leg amputations, hip, pelvic, and spinal surgery.

Pulmonary embolism is not a disease but a complication of thrombosis, or blood clotting, in veins in some other part of the body, most commonly the deep veins of the legs (DVT).  What happens typically is that blood clots in the leg veins and a piece or pieces of the clot break off and are carried to the right side of the heart where they’re pumped into the arteries feeding the lungs.  Depending on their size, the clots can get stuck and block some of these arteries.

Approximately 10 per cent of people who develop PE die in the first hour as a result of massive clots.  Untreated, approximately 30 per cent of people who are diagnosed with PE die, usually from recurrent clots.  If they are treated with anticoagulants, the mortality drops to less than five per cent.  Less than five per cent of patients have another PE while on treatment, but 30 per cent of them will have another PE in the ensuing decade.

Historically PE was diagnosed by scanning the lungs after injecting a radioactive substance. Greatly reduced blood flow, or none at all, to part of the lung would show as an area of reduced radioactivity on the scan.  In treated patients with PE, 36 per cent of lung scans returned to normal in five days, 52 per cent had resolved by two weeks and 73 per cent had resolved within three months.  But this is a relatively crude test that detects only fairly large defects.  The preferred test now is contrast enhanced high resolution CT of the lungs.

The classic presentation of pulmonary embolism, “abrupt onset of pleuritic chest pain, shortness of breath, and hypoxia,” is rarely seen.  Rather, patients typically experience vague, nagging symptoms that are very difficult to diagnose.   Studies of people who died from pulmonary embolism show that at autopsy most of them had nonspecific symptoms for a few weeks before they died and 40 per cent of them had actually seen a physician about these symptoms, but PE had not been diagnosed.

One study showed shortness of breath (73 per cent), pleuritic chest pain (66 per cent), cough (37 per cent) and coughing blood (13 per cent) as the most common symptoms in PE.  Other presenting symptoms include seizures, syncope, abdominal pain, fever, productive cough, wheezing, decreasing level of consciousness, new onset atrial fibrillation, flank pain and delirium in elderly patients.  It should be obvious that most patients who present with these symptoms will not have PE.

PE Risk Factors

The following risk factors have been identified for PE.  Travel of four hours or more in the past month, surgery within the last three months, malignancy (especially lung cancer), history of thrombophlebitis, trauma to the legs or pelvis during the previous three months, smoking, central venous instrumentation within the past three months, stroke, paresis, or paralysis, prior pulmonary embolism, heart failure and chronic obstructive pulmonary disease.  Another study had a list of risk factors twice as long!

Pulmonary embolism generally occurs in one of these three ways:

  • The blood vessel linings are damaged and clots form
  • The blood flow changes so that blood either sits still and clots, or blood flow becomes turbulent and damages the endothelium
  • In blood that’s abnormally likely to clot due to multiple genetic abnormalities.

The bottom line is that PE is relatively common, often undiagnosed, and can occur in many different settings.

As a result of this challenge, a scoring system has been developed to quantify the risk of a person having a PE. The accompanying Table indicates the greatest risk is having a DVT and no other probable diagnosis. Next is a rapid heart rate, immobilization, history of DVT, coughing blood and cancer.  Even with this tool, many cases of PE will not be diagnosed.

When a blood clot or clots block part of the circulation to the lungs, several things can happen.  If the obstruction is very large, the backpressure on the right side of the heart can cause problems or death.  The lungs will have increased alveolar dead space and there can be hypoxemia and hyperventilation.  If the obstruction is smaller there may not be too many signs or symptoms.  Fortunately, pulmonary ‘infarction’ is uncommon because the lungs have two circulations and when one is blocked the second will keep the lung tissue alive until the first blockage resolves.

Normally the clots resolve within a few weeks of the person starting treatment and the lungs heal.  Unfortunately, sometimes the clots do not resolve and/or significant scarring can result.  In addition, some people continue to generate clots in the veins and continue to shower the lungs with emboli.

Diving Considerations

So what is the significance of pulmonary embolism for diving?  If you have a PE, you must be treated with blood thinners, usually for six months.  This will dramatically reduce your risk of dying from the PE and/or having a recurrent PE during this time period.

While you are taking blood thinners you should not dive.  Diving is an activity where the risk of trauma is quite high and a person taking blood thinners who suffers trauma has a significant risk of a massive bleed.  Although the risk is very low, some forms of Decompression Sickness involve bleeding, especially into the spinal cord.  If a diver has this happen and they are taking blood thinners, the bleeding will be much worse and the outcome severe.  It is also probable that bleeding is more likely to occur in a diver on blood thinners who experiences ‘decompression stress’, even if he or she is not ‘bent’.

But what about a diver who has a PE, is treated with blood thinners for six months without problem, and is then off the blood thinners and is doing great.  Can they return to diving?

There are several considerations.  After PE many people have permanent changes to the right side of the heart, presumably from the backpressure created by the PE.  Everyone should have a cardiac workup.  Their ability to return to diving will depend on their exercise capacity and any heart abnormalities that are detected.

A significant number of people will have permanent changes in their lungs after PE.  Full pulmonary function tests and high resolution CT should detect most significant changes but small areas of abnormality will not be detected.  High resolution CT with contrast is a more sensitive test but the increased risk and cost is probably not justified.  The advisability of the person returning to diving will depend on what is found.

If the cardiac workup and the lung studies are completely normal there are still some concerns.  Small areas of damage may not be detected.  In arterial gas embolism the area of damage in the lungs is often as small as the tip of your little finger and in many cases the area of damage cannot even be found on autopsy.  Never forget that arterial gas embolism (AGE) and pulmonary barotrauma are shallow water problems.

In addition, 30 per cent of people who have had a PE will have a second one within 10 years.  If that happens, they will need to be on blood thinners for the rest of their lives.  Finally, the recurrent PE may be asymptomatic, but still put the person at risk of AGE.  Anyone diving after a PE will almost certainly have an elevated risk of problems.


Clinically suspected deep vein thrombosis (DVT)


Alternative diagnosis less likely than PE


Rapid heart rate


Immobilization within past 4 weeks


History of DVT






Total score of greater than 6 indicates a high probability of PE, a score between 2 and 6 moderate probability and a score below 2 low probability.











20 Comments Leave A Reply

20 Responses to “Pulmonary Embolism and Blood Thinners”

  1. Chris Menjou

    I appreciate the article as this issue is not well covered.

    However, and with all due respect, I think the absolute conclusion “While you are taking blood thinners you should not dive” is neither supported by the science nor responsible without any information as to a particular diver’s circumstances. If trauma risk were a sufficient basis alone for participation in a particular activity, there would be scant few activities available to those of us on thinners. We may need to make adjustments (i.e., I would not go on the Galapagos Aggressor again and be 24 hours from land), but the risk of trauma alone is not a contraindication for diving.

    As for DCS bleed complications, is there any scientific study showing a statistical significance between thinners and DCS-bleed complications? What is the increased risk? 5{c383baab7bef8067e8c9786a45d8006c492489841a98fe37723e304bb1ddd030}? 10{c383baab7bef8067e8c9786a45d8006c492489841a98fe37723e304bb1ddd030}? .001{c383baab7bef8067e8c9786a45d8006c492489841a98fe37723e304bb1ddd030}? My UCLA hematologist explained this to me early on but, noting the rarity and my DCS free history, supported my diving.

    For the record, I was cleared by a leading hyperbaric doc here in L.A. to dive on thinners (as well as a UCLA thrombophilia specialist), following a consultation, history and PFO test. In addition, I race triathlons, including Ironman, ocean swim, trail run, zip line, paddle, snowboard – all of which I am sure would be absolutely contraindicated if trauma risk alone was enough to bar participation.

    Of course, as with most medications, one should consider whether diving is appropriate on thinners. But a blanket statement that one should not dive without taking other factors into account – prior DCS hits and profiles? INR range? INR stability? Self testing? Age? Reason for thinners? ability/willingness to dive conservatively? EANx? – is unwarranted. Rather, it is a question that each diver should consult with his or her physician, with referral to a hyperbaric and/or thrombophelia expert as appropriate, and make their own decision

    My fear is that the next diver that thrombolizes with Factor V and performs the inevitable google search will run across an opinion by an M.D. that they will never dive again. When, in reality, they can live a normal life and do those activities that bring them joy, and not have to live wrapped in bubble wrap.

    Just one anticoagulated diver’s opinion

    • zig smigaj

      I agree with Chris Menjou on that each individual should consult a hyperbarics doc before deciding to quit diving after being told to do so by their physician. I would slump into depression if I was told I could never dive again…. I would have to take up some other risky sport just to compensate, such as skydiving or playing piano in a brothel.

    • kevin lemar

      Thank you so much for this. I’m a diver that has just snapped my achilles tendon & now have what I’m told is minor bloodclot in my lower calf.

      I am on 30mg Xerelto per day.

      Been told I will be able to fly in 4 weeks & return to diving in 3 months.

      Adult well balanced omments welcomed

      • janine

        Hi Kevin, I would be interested as to what outcome you have with your achilles tendon.
        I had a PE 2 years ago, followed by another one 6 months later. Doctors cannot work out where it comes from. But I had a diving accident, falling into the boat with my heavy equipment and snapped my tendon in 3 places. Was operated on, that was 8 years ago. Never stop having problems with that leg, swelling, soreness, etc. I still believe my PE comes from that operation. Though scans on my legs prove nothing. Doctors will not let me dive again as I have to stay on blood thinners. Which is most upsetting. What outcome did you have? Interestingly, between my leg injury and my 2 PE, I flew long distances and did many dives!!! Think doctors are not always right.

    • Roger Mac Danold HTCM/MDV USN (ret.)

      Age, physical condition HSX of ignited tobacco and other vegitation will determine risk. If you have a circulatory issue then take up toy repair or tire inflation and giver up breathing air/mixed gases under pressure. Initial issues at depth can often be resolved. Chronic stupidity has NO treatment table.

      • Matthew

        Hi Rodger, your comments are not very helpful..are you saying that people on “blood-thinners” should not dive at all?

  2. Amy

    I moved to Englewood FL…Gulf of Mexico. Paradise. I enrolled in a Scuba Certification class last week, something I’ve wanted to do my whole life. I was diagnosed with PE three days later. I was very disappointed when the ER doctor told me that i would not being diving next week…I was so excited to start. My primary care physician said it would be at least 6 months before I could dive…but he did not say I would never be able to. Im only 42 and otherwise healthy…as far as I know. My Doc said as long as all goes well with treatment of my PE I should be able to dive by the end of the year no matter if I’m blood thinners or not. It will be a long 6 months but worth the wait. I could have had a very different outcome if I wouldn’t have gotten diagnosed when I did:)

    Salt Life :=))

  3. Chris Glynne

    I too get rather aggrieved at M.D. statements that anticoagulants and diving are not compatible.
    I had a very serious Portal vein Thombosis in 2000 that was subsequently, partly explained by a homozygous result for pro-thrombin gene mutation. I took up diving as a substitute for not being allowed to play rugby anymore (I appreciate that contact sports are a bad idea). About a year later when I was now smitten with scuba a doctor tried to tell me I should not be diving. I sought varied and wide-ranging opinion including from hyperbaric experts… The negative opinion seemed mostly to do with the fear of neurological repercussions of any potential case of spinal or brain DCS.
    I finally found some doctors who were prepared to take a more pragmatic, risk analysis view.
    With them I formulated a protocol which was based around mitigation the key risks… Diving nitric on air tables to reduce nitrogen loading, doing ultra cautious depth-stops almost like a deco-dive so that any residual nitrogen is heavily offloaded. I even go to the extent of using a 1.5l pure O2 pony cylinder for the safety stops on any dive deeper than 20m – having trained as an advanced nitrox diver.
    I manage my warfarin with a personal testing device and test the morning of any diving to ensure my INR is between 2.0 and 2.5. If it’s outside that range I dont dive. If I can’t use nitrox then I dont dive below 20m.
    I ensure I do everything possible to reduce DCI risks – hydration, strict dive planning and plenty of buoyancy practise to ensure good safety stops, etc.
    Of course there is nothing I can do to mitigate the random risks that might lead to a case of DCI but then I can’t predict/prevent a random road accident either.
    So, I manage the manageables fastidiously and accept that anything outside this carries a theoretical (with some scientific evidence) extra risk.
    I will be on warfarin the rest of my life and I accepted that my life-love of rugby had to be given up. However, armed with a sensible and cautious diving protocol, a Coaguchek test machine and a strong sense of discipline I dive (and ski) to my heart’s content.

    • Dylan Skilton

      October 2014 I was diagnosed with a large DVT down my right leg and a PE. I am now on Warfarin for the rest of my life. Being a student studying Marine Science and hearing that diving is a very bad idea, I feel confused as well as upset.. what are the risks associated with diving and being on blood thinners? is it only the chance of hitting my head on the dive or cutting myself on coral or a rock the only main risk of bleeding, is that why they say don’t dive because your at risk of an accident happening?.. Does decompression sickness risk rise while on warfarin?

    • Eileen

      Thank you for this. I played rugby throughout college and after, then burst a cervicospinal disc in an alumni a gamer in 2011…no more rugby, ever. I too started non-contact sports–scuba diving and sailing. 5 days ago I had a pulmonary embolism and am on Xarelto. I will be looking for physicians who are willing to work with the fact that I want to live, not just exist.

    • Steve

      Thanks Chris for your comment. I too was a rugby player and after multiple PE’s have been on Warfrin for about six years and for the rest of my life. On discharge my doctors told me I should no longer ski, bike, run marathons, etc. OK no rugby – I get that but I continue to do every other non-contact sport and am starting my diver certification this month. I am sure the statistics would show that I am far more likely to die in a car accident whether I am on blood thinners or not than a dive trauma. Play it safe or shoot the boot? Filler er’ up!

  4. Dylan Skilton

    I got sick at the end of last year with blood clots and a Pulmonary Embolism, and ive read a few articles saying if your on blood thinners you cant dive.
    To complete my university degree I will need to dive. Im still unsure to whether the blood thinners increase the risk of bleeding in relation to the diving apparatus or just the chance of an accident happening in the water where I may hit my head – if this is the case I can take precautions to minimise risk and i will dive but if it has something to do with diving and pressure I wont. From what ive read I am under the impression that it is the risk of chance
    If anyone has any insight or previous experience with this issue, I would love to hear about it..


  5. John Smith

    I’ve recently had a PE (6 weeks ago) and it’s more than likely cleared but early days and a few more tests ahead to confirm it’s removal and whether i’ll be on BTs permanently or not. While at hospital doing more blood tests and setting up scans, i asked teh doctor about diving. and without skipping a beat, she said it’s fine and recommends a max depth of 30m. For me it’s still a no, well not recommended, as I need to complete some scans etc and get blood work back, but once on BT’s it’s seems not a problem. Obviously consult your DR, as mine had my history in front of her, so could comment for me.
    As with any sport it’s making an informed choice on whther you do it or not. Fit and healthy still brings plenty risk to all sorts of sports, but I agree with Chris M, blanket statements doesn’t bring anything to the table, and I can understand from a posters perspective they need to cover themselves when discussing topics like this. Best go to your Dr and get a proper informed decision on your situation.

  6. Bea Wright

    As much as I love diving, I tend to love life a bit more! I’m an RN, an after reading this article and having two clots one called a “saddle clot” which general is found only in the morgue, I can’t see risking everything because of a stupid decision. I think God has a different plan for me and I don’t think it’s diving. Thank for the information!! 🙂

  7. kurt

    i just turned 67, had a dvt 6 years ago that has cleared within the last year. i wear compression to manage the on-going swelling due to valve damage. also a PE at the time. Cause was apparently factor 5. and am on coumadin for life. i was a certified diver in 1973, but have not been down for about 40 years. i’m thinking about getting re certified prior to a trip to the great barrier reef. might be a dumb idea? for age 67, i’m fit,, not fat. do mile swims in the pool with no major effort or ill effects.

  8. Melissa

    With such significant statistics on these conditions, one would think that there would be citation of actual research or studies to back up this information.

  9. Andy James

    For what it’s worth I can give my experience – but everyone is different. In 2010 I had dvt and a large saddle PE. I was in hospital for several days and then on warfarin for 6 months. Since then I have done over 200 dives without issue including galapagos and regularly dive below 30m. I have a dive medical every year and am now 51. Sadly I have just been diagnosed with another dvt although thankfully not PE and probably developed as a consequence of a cycling injury to my knee as I train for a very long sportive week. I am meeting a venous surgeon to understand my options and 3 weeks into blood thinners again have started cycling again. I aim to get to a position where I can resume my diving as well by the end of the year. Everything in life is about risks – it’s about balancing and mitigating them.

  10. Terry Nicholson

    I had a year of tests trying to find the cause of breathlessness on exercising. Eventually I was diagnosed with multiple PE’s. I was given a 6 month course of Rivaroxaban (Xarelto) anti-coagulant which seemed to do the trick. This situation coincided with the ban, from UK Government, on flights to Sharm El Sheik, my preferred diving destination. I decided to delay my return to diving until the ban was lifted, I’m still waiting! Meanwhile I have been diagnosed with a repeat of the emboli and am now on anti-coagulants for life. I would dearly like to return to diving but realise I will need to prove fitness in order to get insurance. Is the way to ascertain clearance to dive (or not) through a specialist Hyperbaric Doctor and, if so, where do I find one? I’d appreciate any comments on the likelyhood of gaining the go ahead ( I do feel as fit as a fiddle) and any pointers towards a specialist doctor if needed. Thanks in anticipation.

    • Glynn Jones

      Hi Terry

      Did you resolve this?

      I’ve recently had a PE and looking to uncover if/when I might be able to dive again.

      Many thanks

  11. Ken Tuttle

    I think it all comes down to liability.
    Doctors are justifiably terrified of getting sued if something goes wrong.
    There is no upside for them offering an opinion.
    I would guess that I am taking a much bigger risk driving my car on blood thinners than going on a diving vacation.
    The bleeding from a simple auto accident could be fatal, but no one is saying that I shouldn’t drive to work every morning.
    There are people who never get off blood thinners because their doctors are afraid their patients could have another clotting event. Leaving people on thinners for decades improves the doctor’s statistics by avoiding repeat thrombosis. There is no stat on whether or not thinners are more likely to kill people in accidents. Imagine dying in an accident because your doctor wanted better looking numbers in some professional report.
    I say, “be active.” Eat a good diet. Get off the thinners if you can and replace them with natural dietary blood thinners. Ginger, Garlic, Turmeric, Cinnamon, Omega3 fish oil, salmon… There are many things that could help you avoid clots.
    If you rely on natural blood thinners and baby aspirin, you can reverse their effect in a few days by avoiding them. You could probably go diving safely. Probably. Too bad no one with a PhD has the balls to take a stand for divers.
    Ultimately, the risk is yours to assume.
    Live your life with whatever level of risk you find comfortable.
    If you never do anything ever again because you are afraid, IMHO you are already dead.


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