Focus your question & identify the main concepts
Finding a few articles on a particular topic is usually easy. However, making sure you aren't missing relevant articles can be trickier. The PICO acronym can help if your question is a clinical query. Essentially it boils down to thinking about what concepts MUST appear in your articles. Think about the:
Often, expert searchers will start by searching the elements of the Who and What first (P + I). If there are too many results or you have a very specific outcome, you can consider whether or not it is appropriate to search on your outcome of interest, too. Many abstracts do not contain much information about all of the outcomes included in the full text. So limiting your search to include a specific outcome will likely mean you'll miss relevant articles. Consider the scope of your question and timeline when deciding on how to approach your search.
State your question(s) as specifically as possible:
Identify the relevant concepts for your question (the PICO model can be helpful)
| P (patient or problem) | post heart attack; low left ventricular ejection fraction of 30%; elderly |
| I (intervention) | implanted defibrillator |
| C (comparison) | none or usual standard of care |
| O (outcome) | mortality |
Four Tips for Searching PubMed
Start your search from the Advanced page.
In the lower query box, type in your first concept heart attack and click the carrot drop down arrow next to search to select Add to History.
Check the Search Details!
Scroll down to view your search history and click the carrot to expand the details.
You should check to see that PubMed found an appropriate Medical Subject Heading for your term. As you can see, PubMed found "myocardial infarction”[MeSH Terms]. That's great! (We will show you later what happens if it didn't find an appropriate MeSH term.) You'll see PubMed also used your concept, heart attack, in the search.That concept was searched in [All Fields]. That means it looked in fields such as the title, abstract, journal name, authors, etc. Using a combination of both keywords and MeSH terms is the best way to search PubMed.
Why check the Search Details?
NOTE: “Quotations” & truncation symbols* turn ATM off
Add and combine concepts using Boolean operators.
Let's go ahead and search the rest of our concepts!!
Search left ventricular ejection fraction and check the Search Details:
PubMed tries to find what it thinks is the most relevant term(s). In this case it couldn't find an exact MeSH term for left ventricular ejection fraction. It broke up your concepts, so left was only searched as [All Fields] and ventricular ejection fraction was translated to a related MeSH term, stroke volume.The ejection fraction is the volumetric fraction of fluid ejected from the heart chamber with each contraction. Stroke volume is the volume of blood pumped from the left ventricle per beat. This concept definitely seems relevant. But is it the best term? When trying to find the most specific and relevant MeSH terms for your concepts, it can be helpful to go to the MeSH Database.
Searching the MeSH Database
While on the Advanced page, click the Click the 
icon on the right above the two search boxes.
OR
From the main PubMed page, click the MeSH Database link (bottom right of screen).
Search left ventricular ejection fraction
NOTE: like a thesaurus you can only search one concept at a time in MeSH
Uh oh! No items found?!
Let's try searching just ejection fraction
Review the options:
Click on Ventricular Dysfunction, Left
You can review the definition as well as the broader and narrower terms (bottom of the page) to decide if this concept would be useful to include in your search.
NOTE: PubMed will include all narrower terms automatically in your search. Sometimes moving up or down the tree to broader or narrower terms can improve your search.
To use this term in your search, click the "Add to search builder" button on the right.
Note: If you were interested in other terms, such as stroke volume, you could go back and add that to your search as well (remember to use OR between similar or related concepts).
Don't click to Search PubMed just yet!
Before we do that, let's remove the "quotes" as well as the [MeSH] from the search first. Then we can let PubMed do its magic of finding and searching both the MeSH term AND the concept as keywords (so in Titles and Abstracts). This will help you be more comprehensive and make sure you find the newest articles even if they don't have MeSH terms attached to the article yet.
In the PubMed Search Builder box, remove the "quotes" as well as [MeSH] from the search term
Click Search PubMed below the PubMed Search Builder box.
After conducting a search in PubMed, you should get into the habit of going to the Advanced page, scrolling down and checking the Search details box to ensure you have appropriate MeSH.
Go back to your search history by clicking on the Advanced link. NOTE: Your searches are temporarily stored here while you work (up to 8 hrs unless you shut your browser completely down).
You'll notice that you get a bit less now. While this might be worrisome, remember the other search mapped to Stroke Volume which included more than just the left ventricular dysfunction. It's important to be specific in your searches to reduce the number of irrelevant citations.
Finding all the relevant citations -- not just a few -- is part of the evidence-based process and enables you to make the best decisions with your patient. Missing a key article could affect your clinical decision making.
Now we need to find a MeSH term for our "I" concept implantable defibrillator.
On the Advanced page, scroll up to the Query box (2nd box), and type in your intervention, implantable defibrillator.
Don't click search - click the chevron next to the search button and click Add to History.
Scroll down and open up the the Search details (see a trend here?).
Whoa! PubMed kind of got what we meant here but this is definitely not great. Brainstorm other ways to express this concept.... maybe you've heard it called an ICD? Let's try that!
When you see only [All Fields], that's PubMed telling you it didn't really know what you meant so it only searched that concept in titles and abstracts. You are likely missing a lot of relevant articles. PubMed doesn't always do well with acronyms. Checking the Search Details will let you know what has happened to your search. Again, with any of these three searches you'll find some on the topic...but also worry about what you might have missed!
What does ICD stand for...? Search implantable cardioverter defibrillator:
BINGO! This seems like the best and most specific way to get at the intervention. If you wanted, you could broaden your search to:
(implantable cardioverter defibrillator OR icd)
Your final search would be combined with Boolean like this:
heart attack AND ventricular dysfunction, left AND (implantable cardioverter defibrillator OR icd)
OR
#1 AND #3 AND (#5 OR #6)
Now it's time to refine your results with appropriate limits that match your PICO like age, study design, etc. Click on the Results number to go to your PubMed results page. Click the link below to learn more about the filters available to refine your search.