know the tech you love

Monday, March 31, 2014

Opening day in baseball, notwithstanding the Dodgers and Diamondbacks in Australia, and the latest experiment to meld the on field judgment of the umpire with the technology of instant replay. The overarching goal to get the right call can’t affect the flow of the game and yet that balance has been difficult to achieve in other sports. And in medicine, that same issue of when and where to invoke technology also exists. While devout fans may consider sports life and death, in medicine it can be, if an error in diagnosis is made.

For all that is high tech in medicine from blood tests to CT, MRI and PET scans, diagnosis begins with history and physical examination. The conversation with patient (including perhaps family members or caregivers) starts the process of differential diagnosis, making a mental list of what might be the cause of a symptom, usually from most common to least likely, but also including most potentially lethal. Physical examination adds more clues to the decision tree and then the art of medicine kicks in. Is the diagnosis solid enough that nothing more needs to be done, no more tests ordered or does technology need to be added. And if tests are ordered, how are the results going to affect patient care.

With the stroke of a pen or the click of a mouse, a doctor may order tests that might not affect patient outcome. Alternatively, not performing those tests might miss a critically important diagnosis. The test may yield a false positive, one that points to a condition that does not exist and causes the patient to be taken through a cascade of procedures that weren’t needed. False negative results might give inappropriate reassurance that all is well, when that was perhaps not necessarily the case. The purpose of technology is to decrease the error rate in coming to a diagnosis, but that error rate never becomes zero.

Clinical decision rules have been developed for the use of many tests but the bottom line often gets lost in translation. The Ottawa CT head rule is a prime example. It helps decide, based upon what happened to the patient and what was found on physical exam, whether a CT of the head is required to look for bleeding in and around the brain. Its use, though, is limited to those aged 16 to 65 and if a CT is not recommended by the rules, it does mean that there is no bleeding present but rather, no injury exists that would require surgery. Appropriately not ordering the head CT would save the patient unneeded radiation but the patient needs to understand the decision making process.

There are blood tests that may have the same issue. While patients who have chest pain primarily worry about their heart, there are many other potential diagnoses that could be listed in the differential and some of them are just as lethal as a heart attack. The history and physical exam give direction as to whether any tests are even required.

  • When heart muscle is irritated it may leak troponin, a chemical which can be detected in the blood, however it may take 6 hours or more for the blood test to turn positive after the onset of chest pain. Running the test too early can yield a false negative in a patient who might actually have narrowing of the arteries to the heart.
  • For a patient who might have a pulmonary embolus or blood clot in their lung, a d-Dimer blood test is a helpful screening tool. It is a chemical that is released when a blood clot starts to dissolve but it cannot tell where the blood clot is located. For that reason it will turn positive in a patient who was pregnant, has had surgery or was a trauma victim. Ordered in that situation, a false positive test might turn the search in the wrong direction and perhaps result in an unneeded CT scan of the chest looking for that blood clot.

In some patients, the test is all about timing. In a person with appendicitis, it takes perhaps 12 hours for enough inflammation to occur to be seen on abdominal CT or ultrasound. Ordering the test too early and there might be false reassurance. In patients suffering with a dissecting thoracic aortic aneurysm, a tear of the major artery that leads away from the heart, the initial chest x-ray might be normal and clinical suspicion may be all that drives the doctor to look harder for that diagnosis.

Replay is now the reality in sport. Perhaps it can enhance an umpire’s call, but when technology invades the art of the game, the question needs to be asked whether it’s that important to be perfect. Science and technology advance at a rapid rate but understanding how to use them appropriately at the bedside returns the art to medicine. While being perfect is the goal for every patient visit, that reality does not exist. Always perfect is not possible but minimizing errors is doable. In medicine, replay happens and is called peer review. Errors, complications and unexpected deaths are reviewed, trying to learn what happened and how to prevent the next mistake. It isn’t instant but the lessons learned from yesterday’s errors allow tomorrow’s care to hopefully be better.

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