Title: Bayesian decision making in primary care or how to stop people dying of chicken pox
1Bayesian decision making in primary care or how
to stop people dying of chicken pox
- Trisha Greenhalgh
- Professor of Primary Health Care
- UCL
2Before we startWhat is primary health care?
3Hospital medicine
- Distinguishing the clear message of the disease
from the interfering noise of the patient as a
person. - Marshall Marinker. The mythology of Hilda
Thompson - In Greenhalgh T and Hurwitz H (eds)
- Narrative Based Medicine. London BMJ Books,
1998
4Primary health care
- In secondary care diseases stay, but patients
come and go, whereas in primary care patients
stay but diseases come and go." - Iona Heath
- The mystery of general practice.
- London Nuffield Provincial Hospitals Trust, 1995
5Primary health care
- First-contact care, delivered by generalists,
dependent on teamwork, which is accessible,
comprehensive, co-ordinated, population-based,
and activated by patient choice. - Pat Gordon and Diane Plamping
- Extending Primary Care. Oxford Radcliffe, 1996
6Primary health care
- Doing simple things well, for large numbers of
people, few of whom feel ill. - Julian Tudor Hart
- A new kind of doctor. London Merlin Press,
1998
7Case historyA patient with query chicken pox
8A patient with chicken pox
- It was Saturday morning. I was on call from 8.30
am. I got a call from one of my partners, Dr B,
at 5.45 am. He was on holiday 200 miles away but
had been called on his mobile phone by Health
Call. One of his patients had rung Health Call
and demanded a visit by Dr B. No other doctor
would do.
9A patient with chicken pox
- The family had a child with chicken pox. She had
been seen the day before by another partner, Dr
R, who has 24 years experience in general
practice and is also a clinical assistant in
dermatology. She had said it was definitely
chicken pox and prescribed fluids, analgesia and
calamine. -
10A patient with chicken pox
- The child had apparently deteriorated and the
parents were worried. They had decided that only
Dr B would know what to do. Dr B (who was many
miles away) asked me to go round immediately and
examine the child. I was not yet on call and
keen to go for my early morning swim before
surgery. - What should my next move be?
11Intermission getting by as a GP
- You only need to answer three questions
- Are they ill or are they not ill?
- If ill, can I deal with it or does someone else
need to be involved? - If someone else, can it wait 12 weeks or cant
it? - Cecilia Gould
- Crouch End Surgery coffee break, July 1989
12Bayesian decision-making
Pre-test odds of disease X
TEST Y
Post-test odds of disease X
13Bayesian decision-making
Parent phones up to say I think my child has
chicken pox
Pre-testY odds of disease X
O.5
TEST Y
Dr R examines child
Post-testY odds of disease X
O.97
Swab to virology
TEST Z
Post-testZ odds of disease X
O.99
14Bayesian decision-making
- Assume Disease X Patient is seriously ill
15Bayesian decision-making
Parent phones up asking for visit to child with
chicken pox
Pre-testP odds of serious illness
O.0005
TEST P
INSERT QUESTION HERE
Post-testP odds of serious illness
O.005
INSERT QUESTION HERE
TEST Q
Post-testQ odds of serious illness
O.5
16A patient with chicken pox
- I asked
- 1. How old is the child? Answer 15
-
17Bayesian decision-making
Parent phones up asking for visit to child with
chicken pox
Pre-testP odds of serious illness
O.0005
TEST P
How old is the child? High risk age group
Post-testP odds of serious illness
O.005
INSERT QUESTION HERE
TEST Q
Post-testQ odds of serious illness
O.5
18A patient with chicken pox
- I asked
- 1. How old is the child?
- 2. Why the ! are you so convinced that these
guys are not time wasters? -
19A patient with chicken pox
- He said
- For one thing, this family have been on my list
for 17 years and theyve never asked for a visit
before. - For another thing, they go to the most orthodox
synagogue in Golders Green.
20A patient with chicken pox
- And theres one more thing I dont like about
this case. It wasnt the mother who rang, it was
the father. In that family, the father never
does the kids health.
21Probability
- Of calling the doctor out at night
- 1 in 17 years (1 in 6205)
- Of using the telephone on the Sabbath
- 1 in 10,000?
- Of father rather than mother negotiating
- 1 in 100?
Estimate the index of parental concern.
22Bayesian decision-making
Parent phones up asking for visit to child with
chicken pox
Pre-testP odds of serious illness
O.0005
TEST P
How old is the child?
How old is the child? High risk age group
Post-testP odds of serious illness
O.005
How worried are the parents?
TEST Q
Post-testQ odds of serious illness
O.5
23The illness script theory
- We start by learning detailed rules about the
cause, course and treatment of diseases - As we gain knowledge we convert these rules to
stereotypical stories (scripts) - We refine our knowledge by accumulating atypical
and alternative stories via experience and the
oral tradition (grand rounds etc) - Knowledge is stored in our memory as stories
24Illness scripts chicken pox visit
- My febrile child should stay indoors.
- I think my child has meningitis.
- This is the first ever illness in my first baby
- My husband has got the car and Im at home with
the 3 kids. - My husband and I are both working and its not
convenient to take time off.
25Illness scripts chicken pox visit
- My 15 year old daughter definitely has chicken
pox. Ive seen chicken pox in my other kids and
this is different. I think my daughter is going
to die. - DOES NOT FIT KNOWN ILLNESS SCRIPT
26A patient with chicken pox
- I didnt go for my swim. I didnt even stop for
a bath or breakfast. I drove straight to the
house, where all the lights were off. The
father, dressed in Orthodox Jewish style complete
with long black coat and hat, came out to meet me
and apologised that the lights were on a time
switch which he could not override. I got a
torch out of the car boot.
27There were 14 relatives in the room, lined up in
silence. All the siblings had been woken up and
were standing staring at me.
28Narrative drama
- Consulting room is a stage
- The illness story is not told but enacted
- The patients performance is the clue to
diagnosis - Cheryl Mattingly. Healing Dramas and Clinical
Plots The Narrative Structure of Experience. - New York Cambridge University Press, 1998.
29On examination by torchlight, the child was
conscious and co-operative, and had a typical
chicken pox rash.
30She was post-pubescent and somewhat overweight.
Her BP was 90/50 and pulse 100. She was possibly
overbreathing (we all were). She said she
couldnt get up, or even sit up.
31On direct questioning, she said I just dont
feel well. Maybe Im a bit faint. No, I havent
fainted or blacked out but its muzzy and I feel
quite scared that somethings wrong.
32I examined her respiratory system. She had a
respiratory rate of 20 and no focal signs. That
was a shame because I was hoping there would be.
33I found no other physical signs. So I decided to
lie about the chest findings. I admitted her to
Coppetts Wood Hospital by blue light ambulance.
34As I left the room, the father thanked me
profusely for saving his daughters life.
35A patient with chicken pox
- We didnt hear anything for a month, and then got
a discharge summary to say the child had had
chicken pox with disseminated intravascular
coagulation. - The child had initially been admitted to
Intensive Care for 5 days. - The parents had been told she was lucky to have
survived
36Hospital medicine
- Distinguishing the clear message of the disease
from the interfering noise of the patient as a
person. - Marshall Marinker. The mythology of Hilda
Thompson. - In Greenhalgh T and Hurwitz H (eds)
- Narrative Based Medicine. London BMJ Books,
1998
37Primary care at the interface
- Inferring the indistinct signal of serious
disease from the complex, fuzzy and largely
unclassifiable noise made by the patient and
the family in their cultural setting. - Trish Greenhalgh
- RFH Grand Round, January 2003
38A note on stories
- "Neither biology nor information science has
improved upon the story as a means of ordering
and storing the experience of human and clinical
complexity. Neither is it likely to." - Kathryn Montgomery Hunter
- Doctors' stories - the narrative structure of
medical knowledge. - Princeton Princeton University Press, 1991
39A note on stories
- Story
- Actors
- Setting
- Plot
- Trouble
- Surprise
- Kenneth Burke 1945
- A grammar of motive
- after Aristotle 528
40A note on stories
- Medical students learn to take a history i.e.
to distort and sanitise the illness narrative to
fit a standardised formula. - B and M-J Good. Fiction and historicity in
doctors stories. - In Mattingly C and Garro L. Narrative and the
cultural construction of illness and healing. - Berkeley University of California Press, 2000
41Conclusion Stories and Bayes
- GPs may be alert to subtle aspects of the
patients narrative (including the enacted drama
of the acute illness). - These hunches, which draw on personalised and
contextualised tacit knowledge about the patient,
and the accumulated illness scripts of
professional experience, can be articulated
through dialogue - Hospital doctors who dont take the hunches of
experienced GPs as evidence may be missing a
trick
42PS The fascinoma paradox
- Doctors learn to manage common problems by
discussing uncommon ones - When you hear hoofbeats, dont think zebras
- Kathryn Montgomery Hunter. Dont think zebras
uncertainty, interpretation, and the place of
paradox in clinical education. Theoretical
Medicine 1996 17 225-241
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44Case 2A patient with depression
45A story from general practice
- TG a locum GP
- Mrs Christine Morgan a bank clerk
46ACT ONE
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55THE LETTERS
56- Dear Trudy
- Thanks for seeing this 54 year old lady with
depression. She has recently been through a
divorce and is losing the family home. She has
had some suicidal ideation but denies concrete
plans. - She works as a bank clerk but is currently off
sick. She has one daughter who lives locally but
with whom she has little contact, and a four year
old grandson. She has been prescribed Prozac
but I wonder if she is taking it. - Thanks for seeing her with a view to counselling.
I have also referred her to Prescription for
Exercise.
57- Dear Ali
- Thanks for seeing this 54 year old lady with
depression and mild obesity. She went through a
divorce recently and now feels the time has come
to work on her physical shape and meet new
people. - She has no physical contra-indications except the
usual low cardiorespiratory fitness. She is
taking HRT and an antidepressant. Her blood
pressure is normal. - She is off sick right now but when she returns to
work she will need to fit the sessions in around
her flexi-time. Im grateful to you for
organising this.
58ACT TWO(3 weeks later)
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64Textbook medical consultation
- Take a history
- Examine the patient
- Order investigations
- Establish a differential diagnosis
- Prescribe treatment
- Refer if indicated
65The narrative approach
- Takes a holistic view of the problem
- Sees illness as part of a life story
- Places the patient as narrator subject
- Uses the storytelling (and listening) as part of
the treatment - The doctors role is partly to suggest
alternative storylines
66A STORYLINE HYPOTHESIS
67Her marital relationship
Her daughter and grandson
Her physical body
Her friends
ACT ONE A fragmented, inconsistent, unfinished,
unhappy story
Her leisure activities
Her work
Dear Trudy letter
Dear Ali letter
STORYLINE OPTION Psychiatric illness
STORYLINE OPTION Shaping up and meeting people
ACT TWO The back to work plot
68The referral as a twist in the plot
- Summarises the story so far
- Focuses on some aspects at the expense of others
- Attributes causality to events
- Interprets behaviour and assigns motives
- HENCE
- Changes the direction of the story
69- Dear Trudy
- Thanks for seeing this 54 year old lady with
depression. She has recently been through a
divorce and is losing the family home. She has
had some suicidal ideation but denies concrete
plans. - She works as a bank clerk but is currently off
sick. She has one daughter who lives locally but
with whom she has little contact, and a four year
old grandson. She has been prescribed Prozac
but I wonder if she is taking it. - Thanks for seeing her with a view to counselling.
I have also referred her to Prescription for
Exercise.
70- Dear Ali
- Thanks for seeing this 54 year old lady with
depression and mild obesity. She went through a
divorce recently and now feels the time has come
to work on her physical shape and meet new
people. - She has no physical contra-indications except the
usual low cardiorespiratory fitness. She is
taking HRT and an antidepressant. Her blood
pressure is normal. - She is off sick right now but when she returns to
work she will need to fit the sessions in around
her flexi-time. Im grateful to you for
organising this.
71Case 2 Summary
- Conventional medicine draws a linear and rational
sequence of history-taking, examination,
investigation, provisional diagnosis, referral
and treatment. - An alternative view is to see the illness as an
unfinished story. A referral can be a crucial
twist in the plot, and may offer the patient a
range of storyline options.
72Thank you for your attention
- Handouts available from Marcia Rigby
- m.rigby_at_pcps.ucl.ac.uk