Clinical Reasoning Skills

STEPP CourseST1;2014

Peter Macfarlane

• intellectual process; leading to a ‘working diagnosis’ & management- discussion

• some puzzles

• sound medical principle;.. ‘diagnosis precedes treatment’..

• ...right diagnosis...right treatment• ...no diagnosis/wrong diagnosis;..!• APLS/emergency approach vs • classical history/examination/formulation/?

Ix/progress

• Hx /Ex ...the medical student approach, exhaustive data..but no idea what it means!)

• then; hypothesis/analytical/deductive approach

• mental shortcuts (heuristics)• then iterative diagnosis approach...’I know

what’s going on here; ...series of closed questions to check this....

• pattern recognition; ‘ducks’quick: like recognizing a friendslower: patterns/clusters

• Stepwise ‘rule outs’; used to exclude ‘don’t miss’ diagnoses

• probabilistic reasoning; ‘zebras’

‘informal’; e.g. -age -duration illness -’red flags’

• ‘formal’ probabilistic reasoningthe Bayesian approach

• Sensitivity• Specificity• Positive predictive value• Negative predictive value• know the 2X2 table

• SpP IN :

• SnN OUT :

• SpP IN : test(or Sx/Sg) with high Specificity performance, Positive result is a good ‘rule IN’

• SnN OUT : test (or Sx/Sg) with high Sensitivity performance, Negative result is a good ‘rule OUT’

• #

• investigations...beware of pitfalls.-’paralysis by analysis’- treat the child not the numbers-always question whether you know

what the test result means (values,pos,neg), before you start.

-’sometimes the best thing to do for the patient (child) is to spare them the misery of a useless intervention’

• keep it simple; Occam’s Razor (1 diagnosis), but learn how to juggle complex multiple problems..

• Test of treatment• Test of time, beware pressure to act....• ‘don’t just do something, stand there!’• if no diagnosis- keep an open mind, think aloud and

get advice (foster ethos of 2nd opinion)• abandon the ‘diagnosis’ when things don’t go to plan• When the diagnosis is ‘obvious’ ; avoid premature

closure; always ask ‘what else could this be?’ ..........think beyond the obvious; avoid the cognitive trap

• recognize your own biases• #

Test of Treatment

• ‘first do no harm’, Test of Treatment rarely leads to robust diagnosis; nearly always better to use ‘test of time’ (except in critical illness).

• lots of confounders....

‘treatment’ trial

apparent effect

TP FP

uncertain no apparent effect or worse

TN FN?

trial of treatment confounders

• False positives• placebo• spontaneous

improvement/remission• natural fluctuation in

disease process

• False negatives• side effects• wrong

drug/dose/duration• natural fluctuation in

disease process• drug resistant disease

variant

ways to improve test of treatment

• establish the baseline• agree the end point• objective measurement if possible; if not reduce

‘subjectivity’• keep everything else the same• careful thought about drug selection, dose route,

duration• Use the ‘3 step protocol’; multiple trials of n=1• #

• Questions?