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Centre for Evidence-
Based Medicine

Completed Therapy Worksheet for Critical Care Medicine


Cook D, Guyatt G, Marshall J, et al. A comparison of sucralfate and ranitidine for the prevention of upper gastrointestinal bleeding in patients requiring mechanical ventilation.
NEJM 1998;338:791-7

Are the results of this single preventive or therapeutic trial valid?

  1. Was the assignment of patients to treatments randomised? And was the randomisation list concealed?
  2. Were all patients who entered the trial accounted for at its conclusion? And were they analysed in the groups to which they were randomised?
  3. Were patients and clinicians kept "blind" to which treatment was being received?
  4. Aside from the experimental treatment, were the groups treated equally?
  5. Were the groups similar at the start of the trial?

Are the valid results of this randomised trial important?

Sample Calculations

Occurrence of diabetic neuropathy Relative Risk Reduction (RRR) Absolute Risk Reduction (ARR) Number Needed to Treat (NNT)
Usual Insulin
Control Event Rate (CER)
Intensive Insulin
Experimental Event Rate (EER)
9.6% 2.8% (9.6%-2.8%)/9.6%
= 71%
9.6% - 2.8%
= 6.8%
[4.3% to 9.3%]
= 15 pts
[11 to 23]

95% Confidence Interval (CI) on an NNT = 1 / (limits on the CI of its ARR)
= +-1.96 sqrt(((CERx(1-CER))/(# of control pts.)) + ((EERx(1-EER))/(# of exper. pts.)))
= +-1.96 sqrt(((0.096x0.904)/730) + ((0.028x0.972)/711))
= ±2.4%

Your Calculations

Relative Risk Reduction (RRR) Absolute Risk Reduction (ARR) Number Needed to Treat (NNT)
3.8% 1.7% (3.8% - 1.7%)/3.8%
= 55%
3.8% - 1.7%
= 2.1%
[4.0% - 0.3%]
= 47 pts
[25 to 333]

Can you apply this valid, important evidence about a treatment in caring for your patient?

Do these results apply to your patient?

  1. Is your patient so different from those in the trial that its results can't help you?
    No, study included mechanically ventilated surgery patients

How great would the potential benefit of therapy actually be for your individual patient?

  1. Method I: f
    Risk of the outcome in your patient, relative to patients in the trial. expressed as a decimal: 1.0

    = 47/1
    = 47
    (NNT for patients like yours)
  2. Method II: 1 / (PEER x RRR)
    Your patient's expected event rate if they received the control treatment:

    1 / (PEER x RRR)
    = 1/________
    = __________

    (NNT for patients like yours)

Are your patient's values and preferences satisfied by the regimen and its consequences?

  1. Do your patient and you have a clear assessment of their values and preferences?
    Needs to be assessed in each patient
  2. Are they met by this regimen and its consequences?
    Needs to be assessed in each patient

Additional Notes

This study also found that the risk of ventilator associated pneumonia, a purported risk with the use of ranitidine, was no different in the groups that received ranitidine compared to the group that received sucralfate.

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