Pre-test probability in the ED
Stefan Tarnawsky Mar 04, 2019
The March 2, 2019 launch of the Crew Dragon 2 capsule paves the way for the long-awaited return of human spaceflight from US soil.
Consider two patients with chest pain:
- A) stable 24F on OCPs with a history of anxiety.
- B) stable 65M with lung cancer presenting 4 weeks after bilateral knee replacements.
Are you concerned that either has a pulmonary embolism? To address this, you’d look at the pre-test probability: the likelihood — by virtue of their symptoms — that they have a PE. Using a calculator such as the Well Score, we see that patient A has a low probability and patient B has a medium/high probability of having a PE. As such, the guidelines would recommend a different workup for each: likely a d-dimer (or nothing) for A and a CT chest w contrast for B.
I’ve spend the last month in the ED learning a new feature of the pre-test probability: the clinical setting. Consider two patients:
- C) 60F HTN, with 4d of constipation and 9/10 abdominal pain presents to her primary care physician.
- D) 60F HTN, with 4d of constipation and 9/10 abdominal pain presents to the emergency department. Will C and D get the same kind of evaluation? Probably not. The PCP will likely test for blood in the stool, treat their constipation, and refer them for a colonoscopy if they’re overdue. In contrast, in the ED this same patient will likely also have labs drawn and get a CT scan. Why the difference in workup? Because the pre-test probability for significant pathology (cancer, obstruction, volvulus, mesenteric ischemia, diverticulitis) of a patient presenting with abdominal pain in the ED is much higher than one presenting to their PCP.
My committed to Internal Medicine made it difficult to realign my work-up approach to that required in the ED setting. I discovered that I have an innately high threshold for doing tests and drawing labs. I have many justifications for this: reducing costs, reducing time, reducing pain, reducing incidental results, and reducing false positives and the subsequent risks of further tests and treatment. But in the ED, given the higher acuity of patients, a physician must have a lower threshold to perform invasive testing. After all, unlike the PCP – who has urgent care clinics and the ED as back-up, the ED is the final safety net. If a diagnosis is missed in the ED, then the risk of patient harm is very high.
Despite these challenges, I thoroughly enjoyed my ED rotation. My shifts at Eskenazi Hospital were the best opportunity I’ve had to practice patient management. After a quick chart review, I’d be the first provider to interview the patient and perform a focused exam. Then, I’d place my proposed orders in the EMR before presenting the patient to my staff. The whole process should take about 20min — a frantic pace that pushed me to establish priorities and economize my questions.
Given such a structure, I had a wonderful opportunity to explore the limits of my knowledge. After all, this is nothing like a NBME-type multiple choice question. In the ED, the patients’ histories are never linear or clear-cut (but is it really the worst headache of your life?). The physical exam is mired by my own skill (is that optic disc bulging? Maybe a little?) And the orders are not mutually exclusive (Head CT? NSAID? Anti-emetic? Each must be considered independently, knowing the best choice may be to get nothing and simply offer reassurance).
Unlike other rotations — where by the time you present your patient the attending has looked them up in the EMR — in the ED your staff only know what you tell them. And so their clarifying questions provide invaluable and instant feedback on the aspects of the H&P you should have acquired and shared.
Overall, the most important theme of my ED rotation was self-assurance. The need for confidence in the ED is manifold. First, you need the confidence to see the patient, to believe that your knowledge can help them. Next, you need the confidence the present to your staff. To overcome any social anxiety, interrupt their work/conversation, and assert your needs and those of your patient (don’t be timid here, your staff will expect these interruptions). Finally, you need the confidence to make a decision and stick to it. If the question is ‘should my patient get a CT scan?’ then the answer cannot be ‘maybe’. No one benefits from that. Instead: be decisive, justify your decisions, and take full advantage of your mistakes to learn from them.