Tuesday, January 15, 2008

To PE, or Not to PE

Pulmonary embolism.

There. I said it. Just like saying "Lord Voldemort." As "they say," naming your fear is a first step in dealing with it, and we surgeons certainly fear the possibility of a patient experiencing a PE. It is really not a terribly frequent complication of surgical care, but it can be devastating, and even fatal. What is it, and what do we do about it? To answer that question, we first must take a look at how your body makes clot --- it is a complicated cascade of events:

OK. That looks a bit too complicated, especially for a simple-minded surgeon. Maybe we should try another approach. Let's just say that when you cut yourself shaving, and the bleeding stops, it's a result of a rapid interaction of a whole range of clotting factors, tissue mediators, and enzymes. Sort of like having a tornado assemble a VW Bug in your front yard --- right this second!

"But DocSurg," you say. "Don't you worry more about bleeding than clotting?" Er, yes, to a point. Bleeding, in the absence of a genetic abnormality or a dastardly pharmaceutical insult, is generally a surgical issue. In other words, we can get a handle on it the vast majority of the time, thanks to sutures, cautery, and the wonderful action of the clotting cascade (some other time we'll get into the issues of audible bleeding and DIC).

Most folks tend to think about clotting abnormalities and difficulties with surgery in terms of hemophilia, because it is a well-known disease process with well-established treatment. What most do not know, however, is that some patients do not fail to make clot, but rather do so all too well, and often do so well away from the operative field ---most importantly, this problem (venous thrombosis and thromboembolism, or VTE) is more common than hemophilia. And wouldn't you know it, surgery is a significant risk factor for VTE.

I certainly do not want to oversimplify this very complicated issue, but I would like to make a few salient points about VTE associated with surgery in general, and general surgery in particular. Basically, there are two broad groups that are at an increased risk for deep vein thrombosis (DVT) and pulmonary embolism (PE) with surgery:

  • Those with a genetic predisposition to VTE, associated with an abnormality of one of the factors in the clotting cascade --- an example would be a patient with a Factor V Leiden deficiency. These patients are at a significantly increased risk for VTE with trauma, surgery, prolonged inactivity, etc......but may not know they have a problem when they present for surgery. A family history may be unknown or negative. These folks can often surprise surgeons by presenting early after surgery with a DVT or PE, even after undergoing a relatively minor procedure. They may require lifelong anticoagulation.
  • Those patients without a genetic predisposition to VTE --- i.e., everybody else, many of whom have any of a number of other risk factors (smoking, oral contraceptive use, obesity, ....and the list goes on). It is a pretty accurate statement that every hospitalized patient has at least one predisposing factor for venous thrombosis.
What's the difference between the two groups? From a practical standpoint, "forewarned is forearmed," and the knowledge that a patient has a hyperthrombotic state allows a surgeon to aggressively treat them with perioperative prophylactic anticoagulation (how aggressive is debatable, and dependent upon the type of surgery involved). However, every patient undergoing a significant abdominal operation deserves some sort of VTE prophylaxis --- and once again, there are a number of risk factors that dictate the degree of aggressiveness in one's approach (there is a great resource at DVT.ORG that explains the rationale for prophylaxis in great detail).

Why is the idea of VTE prophylaxis important? Because pulmonary embolism is potentially fatal, frequently preventable, and associated with significant morbidity (and cost) in those it does not kill. While the surgical literature is replete with studies documenting this, a reasonabe one was published in last month's American Journal of Surgery --- Postoperative Pulmonary Embolism: Timing, Diagnosis, Treatment, and Outcomes.
Our study included 115 patients. Prophylaxis was administered preoperatively in 31% of patients and postoperatively in 56% of patients. The diagnosis was obtained by computed tomography scan in 74 patients (64%), ventilation-perfusion scan in 24 patients (21%), angiogram in 8 patients (7%), and other modalities in 9 patients (8%). The time elapsed between surgery and the diagnosis of PE varied significantly by patient age (<40>P = .02). The majority of patients with PE were treated with anticoagulation (83%). Morbidity and mortality rates both were 9%.
OK, I lied. This isn't a particularly good study, but it is enlightening for a few things. First of all, they had a documented rate of preoperative prophylaxis of only 31% in these patients --- and while they speculated this could have been an error in documentation, that's a pretty big red flag for any attorney scouring the patient's record. Secondly, the overall incidence of postoperative PE at their institution was extremely low at 0.09%, and remained stable throughout the study period (1999-2004). What is not listed is the overall incidence of postoperative DVT, which is the precursor to PE and may be associated with subclinical episodes of PE.

Additionally, the authors main reason for putting this article out at all is the discrepancy seen in the time following surgery that patients presented with their PE --- younger patients presented earlier than older patients. Although no mention was made of a workup in these patients for a hyperthrombotic process, I wonder whether the younger patients had a higher incidence of this than the older ones. Older patients tend to be less mobile after discharge from the hospital, may have undergone more extensive surgery, and tend to stay a bit less well hydrated after discharge (in my own experience) ---- all things that increase their risk for VTE.

Even though the overall rate of postoperative PE is low, and the mortality rate is low when it occurs, this is felt to be in many cases a preventable problem. And though I am really, really, really suspicious when the government says they insist on everyone complying with a set of guidelines to improve patient care, this time I think they are right --- along with a variety of other alphabet soup organizations, CMS will be looking at DVT prophylaxis as a quality indicator for its rather odious pay-for-performance scheme.

In the end, what should patients who are to undergo surgery do? Never fear, DocSurg is here with a few helpful hints:
  • If you or an immediate family member has had a DVT ---TELL YOUR SURGEON!
  • If you are having major abdominal surgery, ask about VTE prophylaxis --- this may include sequential compression devices or injections of Heparin or a low molecular weight Heparin
  • Get out of bed --- frequently --- and walk. Being mobile decreases your risk for DVT substantially.
  • When you get home, don't just stay there --- get out and walk. Go to the mall. Go to Starbucks. Walk in the park. Just don't park your behind on the sofa.
  • Stay hydrated --- significant dehydration increases the risk for DVT. The best way I can explain this is by comparing your venous system to the oil in your car engine --- increasing viscosity is bad, and the less fluid you have in your system, the more viscous your blood becomes.

So, really, we're partners in this --- we need you to help us keep you from getting a significant postoperative problem.

Thanks in advance!