Application of Conclusions - Interventional

Conclusions about procedural benefit and harm can be derived in research studies and presented in the literature. It is important to consider whether any such conclusions can be applied to your patient, or group of patients. Several aspects that should be considered (1-3) are briefly summarised here.

The first consideration in deciding whether published results can be extrapolated to your patient is whether your patient is so very different from the study population that the results are irrelevant to their management.

If you think that your patient is similar to the study population, make an estimate of whether you think your patient is much more likely, as likely, or less likely to be helped / harmed than a typical study patient. Express this factor numerically (for example 10, 1 and 0.1 respectively). Multiply the NNT and / or NNH by this factor to reach an ‘Adjusted NNT and / or NNH’ for your patient. A spreadsheet can be used to do these, and other, Evidence-Based IR calculations (4). You can access the spreadsheet via the ‘Appraise’ section of this website.

Most IR papers are case series. These provide relatively weak evidence (see Oxford Levels of Evidence (5). Nevertheless, we can use EBM principles to estimate the potential rate of any unspecified complication not observed in a trial of a given sample size. The following table (6) provides an interesting perspective on the number of cases that must be reported before a procedure can reasonably be declared ‘safe’.

95% Confidence intervals on extreme results

References

1. Guyatt GH, Sackett DL, Cook DJ: Users' guides to the medical literature. Ii. How to use an article about therapy or prevention. B. What were the results and will they help me in caring for my patients? Evidence-based medicine working group. JAMA 1994; 271(1): 59-63.

2. Levine M, Walter S, Lee H, Haines T, Holbrook A, Moyer V: Users' guides to the medical literature. Iv. How to use an article about harm. Evidence-based medicine working group. Jama 1994; 271(20): 1615-9.

3. Sackett DL, Strauss SE, Richardson WS, Rosenberg W, Haynes RB: Therapy and harm. Evidence based medicine; how to practice and teach EBM, 2nd ed. Edinburgh: Churchill Livingstone, 2000; 105-167.

4. MacEneaney PM, Malone DE: Applying 'evidence-based medicine' theory to interventional radiology. Part 2: A spreadsheet for swift assessment of procedural benefit and harm. Clin Radiol 2000; 55(12): 938-45.

5. Levels: Oxford University: Centre for evidence based medicine. [ link ]

6. Sackett DL HR, Guyatt GH, Tugwell P: Clinical epidemiology. A basic science for clinical medicine., 2nd Ed. ed. Boston / Toronto / London: Little, Brown and Company, 1991.