Examining the evidence

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An everyman’s introduction to evidence-based emergency medicine 

A patient presents a set of symptoms. You, the emergency physician, reach into your toolbox of knowledge and find a useful clinical answer. A simple machine, right? But have you ever taken the time to unpack HOW you make clinical decisions? How much of your clinical decision-making process do you base on your experience? How much do you base on that one attending who showed you the ropes in residency? On the copy of Rosen’s you’ve had for a decade. Chances are, your decision-making process is a complex combination of factors, but is it balanced? Are you incorporating the best research, or the “best evidence” available into your decision-making formula?

Let’s take an example.


You’ve just seen a three-year-old boy with a ‘barking’ cough that has resolved since his arrival in the emergency department. After examining the boy you tell his mother that her son likely has croup, but given his asymptomatic status, doesn’t require any further treatment. Mom asks if the child’s recovery was due to the ‘steam’ treatment that she gave him at home. She also asks what she should do the next time that he has croup. She admits that she had to struggle with the child during the steam but she’s reluctant to do nothing.
The Clinical Quandary
Does humidified air reverse the symptoms of croup?
Unpacking the Mental Process
First, there is experience, or “clinical expertise”. Healthcare professionals and caregivers have been treating croup with humidified air for at least 100 years. In the home, humidified air is usually generated from hot tap water or from kettles. For safety reasons, hospitals have used cool mist devices as long as they’ve been available. The use of humidified air has been supported in part by the belief that it improves airflow by reducing both localized tracheal edema and the viscosity of secretions.
Second, but no less important, is the personal element of the patient’s preferences. In the case at hand, the mother clearly wants to treat her child’s symptoms. The boy, on the other hand, would rather not be exposed to mist. Any clinical decision you make will have to take these particular desires into account.
The third leg of this decision-making triad is where things get interesting, and where the idea of “evidence-based medicine” comes into play. This leg brings into the decision-making process the best evidence available at that moment in time. In the case at hand, available research evidence actually undermines conventional wisdom about the use of steam for croup patients. Studies have demonstrated a reduction in airway resistance with dry air but not with humidified air.
So, who do you trust? Who is the authority? In 2006, the Cochrane Database of Systematic Reviews evaluated the effectiveness of humidified air for the treatment of croup. From ten pertinent studies the best three were chosen and evaluated. The meta-analysis combined the results from the selected trials for each of the following outcomes: admission rates, clinical score, heart rate, respiratory rate, and oxygen saturation. For each outcome, the combined results showed no benefit from the use of humidified air. The authors reported “The combined results from 20 to 60 minutes in the three studies marginally favoured the treatment group with a weighted standardised mean difference of -0.14 (95% confidence interval (CI) -0.75 to 0.47).” As can be seen from the range of the CI from a negative to a positive value, the results are not precise enough to say unequivocally that there’s no benefit or harm but the accumulated results to date suggest neither.
The Upshot: A thorough review of current research on the topic reveals that with croup patients, we’re faced with a small but unlikely chance that humidified air will benefit the child and similarly, a small but also unlikely chance that it could harm the child.
The Wrap-Up: Let us be clear: The objective of evidence-based medicine is not to replace clinical decision-making processes with the findings from current research. We do not throw experience out the window in exchange for “confidence intervals”. Rather, in this model, EPs integrate the highest quality of research evidence into the decision-making process. In this case, the EP acknowledges the mother’s concerns about wanting to do what is best for her child and explains that there is no scientific evidence that humidified air is effective for croup. He also explains that, other than the potential for burns with the use of steam, there was likely little risk if she did treat him with humidified air the next time he has croup.
Dr. Worster is an associate professor of EM and of clinical epidemiology and biostatistics at McMaster University.

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