ASK DR. BAUGHAN                                                                     March 20, 1998

CARPENTERS, FARMERS, AND EMBOLI

“Would you please write about broken bones and emboli?”

One of my favorite questions for medical students used to be, “If you had to choose between being a carpenter or a farmer, which would you choose?”  Over 13 years, fairly consistently the students chose carpenter over farmer 3 to 1.  They explained that they preferred being able to identify a problem, fix it, then step back and see their finished product.  Farming was an on-going, never finished task, with many factors (weather, soil, parasites, etc.) beyond their control.  I think their choice reflected our society’s values.  Unfortunately, health and  the workings of the human body requires an appreciation for the complex interaction of ecological forces much more akin to farming than to carpentry.  Unless we can accept this, it is difficult to accept or understand many diseases.

Broken bones are excellent examples of this dilemma.  In our minds, we picture a piece of wood that cracks.  We want to straighten it out,  support it with a splint as strong as the wood itself, and that’s it, as good as new.  What is seductive about fractures is that most of the time, that image seems to be “the way it is.”  Once in a while, though, the process goes awry with tragic consequences.

If we could zoom in and examine the fracture site in microscopic detail, we would see a chaotic construction site in a jungle, not a simple broken piece of wood.  We would see torn muscles, nerves and blood vessels leaking fluids, blood and chemicals.  The blood clotting subcontractors would be running all over the place stopping thousands of bleeding sites.  They would be starting chemical reactions that produce clots where they are needed.  Amazingly, 99.9% of the time, the clots stay small and limited to the leg.  However, if the clotting  process continues too long, a clot gets too big, and a piece breaks off and floats downstream to the heart, then the lungs, this is the dread complication called a pulmonary embolus.  Within the bone marrow the blood and inflammatory fluids create pressure within the confined space of the bone and leg, once in a great while, for reasons we cannot yet explain, this pressure forces fats cells from the marrow into the blood stream, which then flow upstream to the heart and lungs.  Fat emboli can be even more difficult to treat than pulmonary emboli.

Pulmonary emboli or fat emboli happen quickly.  They affect half a million people in the U.S. annually; they cause 50,000 to 200,000 deaths a year.  Two-thirds of the deaths occurs within one hour of the embolus.  Why they cause death is also puzzling from a mechanical, carpenter-like perspective.  The blood clot or fat emboli block up blood vessels in the lung, cutting down the oxygen that can get in the blood stream.  But you can clamp off the main artery to the lung and remove an entire lung, and people can still live.  Why should an embolus be different?  With an embolus, the lungs then release a series of chemical reactions in alarm that may lower blood pressure or cause an irregular heart beat that can be suddenly fatal.

We know of several diseases and situations (extensive burns, prolonged immobility, childbirth, certain surgeries) that are high risk for pulmonary  emboli.  We can try to keep the blood flow in the legs moving by exercising the legs, using compression stockings, or by using blood thinners such as aspirin or heparin.  The blood thinners carry the risk of causing too much bleeding.  If a pulmonary embolus occurs and the patient survives the first hour, blood thinners may dissolve clots or prevent further clots, but emboli can be difficult to diagnose because the symptoms are not specific (usually shortness of breath, maybe chest pain) but the tests to prove it take time.  Fat emboli have no specific treatment; we give oxygen and treat blood pressure or heart rhythm problems and hope the patient pulls through.

Emboli remains frustratingly difficult to predict or treat.  Like a farmer looking over the fields, we wonder that healthy crops grow as often as they do, but we cannot take anything for granted.