News

Evidence Based Medicine for The Hospitalist


 

The first step in finding an answer to a clinical question is to ask an effective question. This was the subject of the previous installment in this series, in which the PICOT question format was introduced (see The Hospitalist, Nov. 2005, p. 32). This format leads naturally to effective search strategies, so we optimize our chances of finding quality answers if they exist. There are many possible sources of information that can be searched, however, and the type of question asked can provide valuable guidance as to which sources should be first up for review.

Types of Questions and Where to Look for Answers

Many clinical questions pertain to basic medical knowledge rather than cutting-edge current research. These so-called background questions typically involve such issues as the underlying pathophysiology of a disease, the incidence of the disease, the general treatment considerations for the disease, and overall prognosis for patients with the disease. These questions usually do not require evaluation of the most recent medical literature and can often be answered by reviewing sources of established medical knowledge such as medical textbooks, MD Consult, or UpToDate. In fact, searching for basic knowledge in the current research literature can be exhausting because the focus of most papers is necessarily narrow and therefore too restrictive to properly address knowledge of a general nature.

overview of searchable sources of medical information click for large version

click for large version

The main limitation of these more general sources is that it takes years for medical knowledge to become established, so the most current results will seldom be incorporated. For background questions this is usually acceptable, but if a major breakthrough in our understanding of a disease occurs it is unlikely to be found in these sources. An additional limitation is that the statements found in these sources are often not truly evidence-based—at least not in a transparent or reproducible manner. These limitations are becoming less problematic as resources such as UpToDate strive to add evidence-based reviews and quality measures to their summaries, and also begin to update information much more rapidly as online materials become more standard.

In contrast to background clinical questions, foreground clinical questions are more likely to relate to the management of an individual patient in a specific clinical setting, and are therefore too narrow in scope to be addressed well by the sources best suited for background questions. For example, consider the question posed in the last installment of this series, “Among men over the age of 65 with Stage II renal cell carcinoma, does post-resection chemotherapy result in greater five-year survival than nephrectomy alone?” No textbook will answer a question with this narrow focus. To find an answer we need to be able to sift through the current medical research literature.

Searching for the answers to well-constructed clinical questions is obviously a crucial step in the EBM process.

How to Search Research Databases

The number of medical journals has increased dramatically in the past 20 years. As a result, while it may be more likely that your question has been addressed somewhere, it can be more difficult to locate the paper you need. One approach to this problem is to become skilled in developing search strategies. We will return to this, but an alternative is to utilize secondary journals such as ACP Journal Club (www.acponline.org) or prefiltered sources such as the Cochrane Library (www.cochrane.org).

Secondary journals typically screen articles for both clinical relevance and methodologic quality, making them efficient resources for busy clinicians. The Cochrane Library focuses mainly on systematic reviews of controlled trials of therapeutic interventions. The main downside of these sources is that they may not address your particular question. Therefore, one effective search strategy is to first search a secondary journal or prefiltered source and stop if you find what you need. If you don’t find what you are looking for, you will need to enter the world of the large medical research database armed with a search strategy.

Constructing effective search strategies is perhaps even more of an art than constructing effective clinical questions. Luckily, medical librarians are experts at this and should be your first stop. Not only can skilled medical librarians help you with your searches, they can also teach you efficient ways to conduct simple searches yourself. I will mention a few of these strategies, but these are truly only the tip of the iceberg.

The key elements of searching the large medical information databases such as MEDLINE include an understanding of Medical Subject Headings (MeSH), text-word searching, and combining searches. Mapping to a MeSH term and clicking the “explode” option on the search page will gather not just those papers indexed to the term of interest, but also papers referencing more specific aspects of that term. Clicking on the search term itself will reveal the “tree” of terms related to your chosen search term. For example, try searching MEDLINE for “cancer.” You will be mapped to “neoplasms,” and if you click on that term, you will see a tree of related terms. If you select “explode” for your initial search, you will include each of these related terms, expanding your search. You could also narrow your search by selecting “neoplasms by site” or another subheading, and further refining your approach from there.

Recommended Reading

  • Greenhalgh T. How to read a paper: the MEDLINE database. BMJ. 1997;315:180-183.
  • Guyatt G and Rennie D, eds. Users’ Guides to the Medical Literature: A Manual for Evidence-Based Clinical Practice. Chicago, AMA Press; 2002.
  • Sackett DL, Richardson WS, Rosenberg W, et al. Evidence-based medicine: How to practice and teach EBM. Edinburgh, Scotland, Churchill Livingstone; 1998.

To begin a search, it is helpful to first enter in relevant keywords from your clinical question. Following our previous example, these could include renal cell carcinoma, chemotherapy, and survival. Then you could perform one search for each term, combining them using the search window options. Alternatively, each term could be linked in one search using the AND/OR operators. Further restrictions such as looking only at randomized controlled trials or for specific authors are also possible. Finally, many MEDLINE sites have a collection of saved search strategies for common clinical question types. For example, a saved search strategy for articles on diagnosis (or therapy, prognosis, or any other question type) can provide an effective searching technique based on the expertise of your resident search professional.

Because many of these approaches rely on the way in which an article has been indexed, searching for synonyms can also be helpful. You may search for temporal arteritis and miss articles indexed only under giant cell arteritis, for example. MEDLINE does a good job of mapping these terms to each other, but this can fall short, particularly if you search by text word alone. Being clever with synonyms can be the difference between finding and missing the one key article that will answer your clinical question.

Searchable Sources of Medical Information

“Overview of Searchable Sources of Medical Information” (p. 18) presents a brief overview of searchable sources of information. Becoming a searching expert takes considerable dedication, but fortunately the basic strategies are not overly complicated. Additionally, significant efforts are being made to simplify the steps needed to answer clinical questions, as can be seen in the growing number of secondary journals available for both general medicine and subspecialties.

Summary

Searching for the answers to well-constructed clinical questions is obviously a crucial step in the EBM process. Well-built questions suggest efficient search strategies, simplifying what can be a complex and daunting process. Many resources are available to help with this step, including medical librarians, prefiltered searches, and saved searches for common query types. Once you locate an article addressing your clinical question, the next step is to critically appraise the article to determine whether its results are applicable to your patient. TH

Dr. West practices in the Division of General Internal Medicine, Mayo Clinic College of Medicine, Rochester, Minn.

Next Article:

   Comments ()