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Critical Appraisal: Therapy article

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George G. Lim

on 10 September 2016

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Transcript of Critical Appraisal: Therapy article

Clinical Decision-making
using an article about Treatment

George G. Lim, MD, FPSGS, FPSCRS, FPCS
Professor I, Department of Surgery
Faculty of Medicine & Surgery
University of Santo Tomas

A 72-year old female consults you for hypertension and elevated cholesterol. During your discussion on cardiac risks, she inquires about the need to take an anti-cholesterol drug.

What advise will you give?
Patient
Knowing the patient’s true state is often unnecessary
Treatment error is always a possibility when the diagnosis is uncertain
The need for diagnostic certainty depends on the penalty for being wrong
Decision-making
...making choices
Diagnosis
Should I request for a laboratory examination or treat right away?
Between two diagnostic alternatives, which one should I request?
Treatment
Should I start treatment or observe first?
Between two or more drugs, which one should I prescribe?
old paradigm
Pathophysiology
Common sense
Experience
Experts
Medical Evidence
new paradigm
Medical Evidence
Pathophysiology
Common sense
Experience
Experts
Hypercholesterolemia promotes coronary artery disease thus cholesterol is a risk factor
Lowering cholesterol also lowers the risk of coronary artery disease
If cholesterol is elevated by laboratory examination, it can be lowered by drugs
National Cholesterol Education Program: screen all adult patients and intervene when necessary
Formulate the problem into a question
Conduct a systematic medical literature search
Critically appraise the medical literature
Apply the results
Evaluate the application
Question
Search & select
Among elderly patients who have elevated cholesterol, will anti-cholesterol drugs be beneficial?
MEDLINE
Randomized trial of cholesterol lowering in 4444 patients with coronary heart disease: the Scandinavian Simvastatin Survival Study
Study design?
Case-control
Cross-sectional
Cohort
Cross-over
RCT
Advantages
Quick and cheap
Only feasible method for very rare disorders or those with long lag between exposure and outcome
Fewer subjects needed than crosssectional studies
Disadvantages
Reliance on recall or records to determine exposure status
Confounders
Selection of control groups is difficult
Potential bias: recall, selection
Advantages
Cheap and simple
Ethically safe
Disadvantages
Establishes association at most, not causality
Recall bias susceptibility
Confounders may be unequally distributed
Neyman bias
Group sizes may be unequal
Advantages
Ethically safe
Subjects can be matched
Can establish timing and directionality of events
Eligibility criteria and outcome assessments can be standardized
Administratively easier and cheaper than RCT
Disadvantages
The controls may be difficult to identify
Exposure may be linked to a hidden confounder
Blinding is difficult
Randomization not present
For rare disease, large sample sizes or long follow-up necessary
Advantages
All subjects serve as own controls and error variance is reduced thus reducing sample size needed
All subjects receive treatment (at least some of the time)
Statistical tests assuming randomization can be used
Blinding can be maintained
Disadvantages
All subjects receive placebo or alternative treatment at some point
Washout period lengthy or unknown
Cannot be used for treatments with permanent effects
Advantages
Unbiased distribution of confounders
Blinding more likely
Randomization facilitates statistical analysis
Disadvantages
Expensive: time and money
Volunteer bias
Ethically problematic at times
Provide the BEST evidence of effectiveness
Individuals are randomly assigned (randomization) to either of the groups
Randomization tries to make the groups SIMILAR
They are observed FORWARD in time and their outcomes compared
The outcome can be the cure of a disease, relief of symptoms, or improvement in quality of life
Relevance
Validity
Importance
Applicability
Is the objective of the article comparing interventions similar to your clinical dilemma?
Is the objective of the article comparing interventions similar to your clinical dilemma?
YES
The objective of the study is to compare Simvastatin, an anti-cholesterol drug with placebo
Is the article likely to be true?
Are the results valid?
How large is the size of the effect?
Will the findings work in my patient?
Population of the study (P) – should be similar to the characteristic of your patient
Intervention/comparative intervention/exposure (I) – should include the therapeutic intervention you want to test
Outcome of the study (O) – one of the outcomes measured should be the goal you and your patient wish to work for
Was the assignment of patients to treatments randomized?
YES
The title, abstract and the methodology section stated that the study was a double-blind randomized controlled trial
Were all patients who entered the trial properly accounted for and attributed at its conclusion?
Was follow-up complete?
Were patients analyzed in the groups to which they were randomized?
Drop-out rates are greater than event rates
Gross imbalance in drop-out rates between groups
Worst assumptions lead to opposite conclusions
Were all patients who entered the trial properly accounted for and attributed at its conclusion?
YES
4,444 patients were randomized and analyzed according to intention-to-treat principle.
In the Table for the main analysis, the sum of patients in each group totaled 4,444, the number who were randomized
Were patients, health workers, and study personnel blind to treatment?
YES
The study was a double-blind controlled trial
Were the groups similar at the start of treatment?
YES
Table 1 of the results section showed no major difference in the baseline characteristics between the two groups
Aside from experimental intervention, were the groups treated equally?
YES
There were no planned co-intervention for the two groups
What are the Results?
If you weighed 80 kg after the Christmas holidays, and 60 kg after a summer diet, what would be the ways of expressing your weight loss?
I lost 20 kg (absolute weight reduction)
I am now 75% of what I used to weigh (relative weight)
I lost 25% of my weight (relative weight reduction)
Can the results be applied to my patient care?
YES
Subjects included in this study were patients with angina or MI and elevated cholesterol
Were all clinically important outcomes considered?
YES
The main outcomes considered were new onset of MI, coronary death, and overall cause of death
Are the likely treatment benefits worth the potential harm and cost?
33 patients to prevent 1 death (or save 1 life)
40 mg tab at @ P 25.00
At 365 days = P 18,250
For 33 patients = P 602,250
For 5 years = P 3M
Can the results help me in caring for my patient?
Are your patient’s values and preferences satisfied by the regimen and its consequences?
Do your patient and you have a clear assessment of their values and preferences?
Are they met by this regimen and its consequences?
72-year old patient
Resolution
A 72-year old female consults you for hypertension and elevated cholesterol. During your discussion on cardiac risks, she inquires about the need to take an anti-cholesterol drug.

What advise will you now give?
I would rather not give an anti-cholesterol drug. The benefit is too small for the cost it will take.
I will prescribe an anti-cholesterol drug.
My patient can afford the cost even if the benefit is not large.
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