Department of Medicine

Appraising Evidence

Appraising evidence • Epi calculator
• SI Conversion
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Critical appraisal cheat sheet

('Blue card')

Converting units

Converting to/from Systeme International d'Unites (from MGH Case Records in the NEJM)

Glossaries

Levels of Evidence

  • Table from Oxford-Centre for Evidence Based Medicine

Beyond levels of evidence: more detail for specific study designs

Diagnosis

More information:

Jaeschke R, Guyatt GH, Sackett DL. Users' guides to the medical literature. III. How to use an article about a diagnostic test. B. What are the results and will they help me in caring for my patients? The Evidence-Based Medicine Working Group. JAMA 1994;271:703-7. PMID: 8309035

PubMed:
Abstract - Related articles		   Fulltext options:
EBSCO - OVID - Centre for Health Evidence (free access)

Summary of Bayes theory:

  • Rarely is a test perfect with both sensitivity & specificity equal 100%
  • If a test result is unexpected, it may be incorrect
  • SPPIN and SNNOUT (more from CEBM )
    • For a test to be useful in isolation, needs:
      • sn or sp>90 to 95%
        - or -
        LR+ > 5-10 or LR- < 0.2 to 0.1 (Likelihood ratios)
      • SPPIN - highly SPecific test, if Positive, helps rule IN
      • SNNOUT - highly SNecific test, if Negative, helps rule OUT

Treatment

More information:

Wen L, Badgett R, Cornell J. Number needed to treat: a descriptor for weighing therapeutic options. Am J Health Syst Pharm 2005;62:2031-6. PMID: 16174840

PubMed:
Abstract - Related articles		   Fulltext options:
JAMA - CrossRef - DOI - EBSCO - OVID

Use NNT:

    Probably better for understanding complex information

Limitations of NNT:

  • Difficult math
  • Need to specify length of treatment
  • Does not generalize across different risks of outcome

Evidence tables

A good way to help you dissect an article is to compare it to a similar article - especially if the two articles disagree.

Organize your evidence - sample evidence table

Creating an evidence table may help your organize your thinking and help listeners follow your presentation. Below is a suggested format. We may only discuss 1-2 of your articles in class, but preparing the evidence table will help you identify which articles best support your conclusion.
Study, year Patients Intervention Outcome measured Results Comments

Spring, 2008 (CORTICUS)
PMID: 18184957

RCT


499 patients with septic shock.
47% with adrenal insuff (<9mcg cortisol increase after corticotropin test).

50 mg of intravenous hydrocortisone q 6 hrs for 5 days

mortality

Overall:
  steroid group 55%
  placebo 61% (P =.09)
Adrenal normal:
  steroid group 29%
  placebo 29% (P =1.0)
Adrenal insufficient:
  steroid group 39%
  placebo 36% (P =.69) 

Steroids did not help.
 

However, these patients were less sick than those in the Annane study (note difference in control group mortality).

Annane, 2002
PMID: 17720019

RCT


300 pts, all ventilated.

76% with adrenal insuff (<9mcg cortisol increase after corticotropin test).

 hydrocortisone (50 mg q 6 hrs) &
fludrocortisone (50 mcg qd)		 mortality Overall:
  steroid group 55%
  placebo 61%
  (P=.09)
Adrenal normal:
  steroid group 61%
  placebo 53%
  (P=.02)
Adrenal insufficient:
  steroid group 53%
  placebo 63%
  (P=.02)
 Steroids (with fludrocortisone) helped those with adrenal insufficiency.
 
First study with sufficient power.

Cotreated with fludrocortisone.

Briegel, 1999
PMID: 10321661

RCT

 40 pts hydrocortisone 100 mg bolus, 0.18 mg/kg/hr
(100 kg patient would receive 432 mg/d)		 mortality


shock reversal		 Mortality:
  steroids: 20%
  placebo 30%(insig)
Shock reversal:
  steroids:90%
  placebo: 80%(insig)		 Small size limits power

Bollaert, 1998
PMID: 9559600

RCT

41 patients requiring pressors >48 hrs.

29% were adrenal insufficient (<6mcg cortisol increase after corticotropin test)

 hydrocortisone 100 mg tid x5d mortality Overall:
  steroids: 32%
  placebo: 63%
  (insig)
Adrenal normal (n=29):
  steroids 33%
  placebo 64% Adrenal insufficient (n=12):
  steroids 25%
  placebo 63%
 Introduced role of corticotropin testing - which did not predict response to steroids.

Cronin, 1995
PMID: 7634816

Systematic review of RCTs
730 patients with septic shock in 6 studies		 varying regimens mortality RR=1.07 (95% CI 0.91, 1.26) Much heterogeneity

Lefering, 1995
PMID: 7600840

Systematic review of RCTs
1329 patients in 10 studies		 varying regimens mortality ARR=-0.2% (CI: -9.2, 8.8) Much heterogeneity

No differences between low - vs. high-dose or type of corticosteroid.

The Gram-negative group demonstrated better outcome (-5.6% vs. 1.8% for gram positive).

Conclusion in this example:
The best evidence suggests that in this clinical controversy, the risk of death is reduced, but only in patients with relative adrenal insufficiency and if steroids are combined with a mineralocorticoid.

Calculators