Centre for Evidence-Based Medicine EBM and E-B Guidelines l EBM integrates evidence, expertise, and...

Centre for Evidence-Based Medicine

EBM and E-B Guidelines

EBM integrates evidence, expertise, and the unique biology and values of individual patients.

Local EB Provision ought to integrate evidence, expertise, and the unique biology and values of the local scene.

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EBM and E-B Guidelines

The best evidence comes from systematic reviews (such as Cochrane) and/or E-B journals of 2º publication:» Much more likely (than personal search and

critical appraisal) to be true » Saves the clinician’s precious (scarce!) time

Avoids error and duplication of effort

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EBM and E-B Guidelines

But NO systematic review can (or should try to) identify the “4 B’s:» Burden» Barriers» Behaviours» Balance

They can ONLY be determined at the local (or even patient) level

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1. Burden

The burden of illness, disability, and untimely death that would occur if the evidence were NOT applied

the consequences of doing nothing

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2. Barriers

Patient-values & preferences Geography Economics Administration/Organisation Tradition “Expert” opinion

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3. Behaviours

The behaviours required from providers and patients if the evidence is applied.

All that guidelines can do is specify the former!

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4. Balance

The opportunity cost of applying this guideline rather than some other one.

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Killer B’s

Burden: too small to warrant action. Barriers: ultimately down to patients’

values. Behaviours: may not be achievable. Balance: may favour another guideline

over this one.

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Two monumental wastes of time and energy

First, national/international evidence-summarising groups prescribing how patients everywhere should be treated.

Their expertise: predicting the health consequences if you do treat.

Their ignorance: the local B’s, and whether killer B’s are operating.

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Two monumental wastes of time and energy

Second, local groups attempting to systematically review the evidence.

Their expertise: identifying the local B’s and eliminating the killer B’s

Their ignorance: searching for all relevant evidence; Chinese; performing tests for heterogeneity.

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Applying a study result to my patient

Never interested in “generalising”

Am interested in a special form of extrapolation: particularising

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Extrapolating (particularising) to my

individual patient:

First and foremost: Is my patient so different from those in the trial that its results can make no contribution to my treatment decision?

if no contribution, I restart my search if it could help, I need to integrate the

evidence with my clinical expertise and my patient’s unique biology and values...

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To add Clinical Expertise and Patient’s Biology &

Values:

What is my patient’s RISK ?» of the event the treatment strives to prevent?» of the side-effect of treatment?

What is my pt’s RESPONSIVENESS? What is the treatment’s FEASIBILITY in

my practice/setting? What are my patient’s VALUES ?

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To add Clinical Expertise and Patient’s Biology &

Values:

I begin by considering Risk and Responsiveness for the event I hope to prevent with the treatment:

The report gives me (or I can calculate) an Absolute Risk Reduction [ARR] for the average patient in the trial.

ARR = probability that Rx will help the average patient.

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For example, Warfarin in nonvalvular atrial

fibrillation:

After 1.8 years of follow-up in an RCT: Control Event Rate (placebo) = 4.3% Exper. Event Rate (warfarin) = 0.9% so, for the average patient in the trial,

the probability of being helped, or Absolute Risk Reduction = (CER - EER) = 3.4% ACPJC

1993;118:42

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How can I adjust that ARR for my pt’s Risk and Responsiveness?

Could try to do this in absolute terms:» my Patient’s Expected Event Rate: PEER» and multiply that by the RRR» and factor in my Patient’s expected

responsiveness Clinicians are not very accurate at

estimating absolute Risk and Responsiveness

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How can I adjust that ARR for my pt’s Risk and Responsiveness?

Clinicians are pretty good at estimating their patient’s relative Risk and Responsiveness

So, I express them as decimal fractions:» f~risk (if at three times the risk, f~risk = 3)» f~resp (if only half as responsive [e.g., low

compliance], f~resp = 0.5)

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How can I adjust that ARR for my pt’s Risk and Responsiveness?

probability that Rx will help my patient = ARR x f~risk x f~resp

If ARR is 3.4% and I judge that their f~risk is 3 and that their f~resp is 0.5 then the probability that warfarin will

help my patient = 3.4% x 3 x 0.5 = 5.1%

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Must also consider the probability that I will do

harm:

In the case of warfarin: serious bleeding (requiring transfusion) from the g-i tract, or into the urine, soft tissues or oropharynx.

Absolute Risk Increase = 3% at 1 yr, so ARI estimated to be 5% in 1.8 years

ACPJC 1994;120:52

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…and adjust the probability of harm for my

patient

Again, can express my clinical judgement in relative terms: f~harm

Given my patient’s age, I judge their f~harm to be doubled: 2

then the probability that Rx will harm my patient = ARI x f~harm =

5% x 2 = 10%

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Can now begin to estimate the Likelihood of Help vs.

Harm

Probability of help: ARR (embolus) x f~risk x f~resp = 5.1%

Probability of harm: ARI (haemorrhage) x f~harm = 10%

My patient’s Likelihood of Being Helped vs. Harmed [LHH] is: (5.1% to 10%) or 2 to 1 against warfarin!

…or is it ?

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The LHH has to include my patient’s values

I need to take into account my patient’s views (“preferences,” “utilities”) about the relative severity:

» of the bleed I might cause

» to the embolus I hope to prevent Expressed in relative terms = s~

» if the bleed is half as bad as the embolus, then s~ = 0.5

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On in-patient services in Oxford and Toronto:

When Dr. Sharon Straus has described a typical embolic stroke (with its residual disability) and typical moderate bleed (brief hospitalisation and transfusion but no permanent disability):

for most of her patients, a bleed is only 1/5th as bad as a stroke

so the s~ is 0.2

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So the LHH becomes:

{ARR for embolus} x {f~risk} x {f~resp} vs.

{ARI for bleed} x {f-harm} x {s~}

3.4% x 3 x 0.5 = 5.1% vs. 5% x 2 x 0.2 = 2%

LHH = 5.1 to 2 or 2.5 to1 » (I am more than twice as likely to help than harm my

patient if they accept my offer of Rx)

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We can work out the LHH for most patients <6

minutes

To be feasible on our service: has to be “do-able” in 3 minutes.

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Reactions from our patients

All are grateful that their values/opinions are being sought

1/3 want to see the calculations, perhaps change their value for s~, and make up their own minds.

1/3 adopt the LHH as presented. 1/3 say “Whatever you tell me, doctor!”