Bayesian decision making in primary care – or how to stop people dying of chicken pox

Bayesian decision making in primary care – or how to stop people dying of chicken pox

Trisha Greenhalgh

Professor of Primary Health Care

UCL

Before we start:

What is primary health care?

Hospital 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

Primary 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

Primary 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

Primary 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

Case history

A patient with query chicken pox

A 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.


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.


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?

Intermission: getting by as a GP

You only need to answer three questions:

1. Are they ill or are they not ill?

2. If ill, can I deal with it or does someone else need to be involved?

3. If someone else, can it wait 12 weeks or can’t it?

Cecilia Gould

Crouch End Surgery coffee break, July 1989

Bayesian decision-making

Pre-test odds of disease X

Post-test odds of disease X

TEST Y


Pre-testY odds of disease X

Post-testY odds of disease X

TEST Y

Post-testZ odds of disease X

TEST Z

Parent phones up to say “I think my child

has chicken pox”

Dr R examines child

O.5

O.97

Swab to virology

O.99


Assume Disease X = Patient is seriously ill


Pre-testP odds of serious illness

Post-testP odds of serious illness

TEST P

Post-testQ odds of serious illness

TEST Q

Parent phones up asking for visit to child

with chicken pox

INSERT QUESTION HERE

O.0005

O.005


O.5


I asked:

1. “How old is the child?” [Answer: 15]




TEST P


TEST Q


with chicken pox”

How old is the child? [High risk age group]

O.0005

O.005


O.5


I asked:

1. “How old is the child?”

2. “Why the $#*! are you so convinced that these guys are not time wasters?”


He said:

“For one thing, this family have been on my list for 17 years and they’ve never asked for a visit before.

For another thing, they go to the most orthodox synagogue in Golders Green.”


“And there’s one more thing I don’t like about this case. It wasn’t the mother who rang, it was the father. In that family, the father never does the kids’ health.”

Probability

• 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.




TEST P


TEST Q


with chicken pox”

How old is the child?

O.0005

O.005

How worried are the parents?

O.5

How old is the child? [High risk age group]

The 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

Illness 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 I’m at

home with the 3 kids.”• “My husband and I are both working and

it’s not convenient to take time off.”

Illness scripts: chicken pox visit

• “My 15 year old daughter definitely has chicken pox. I’ve 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


I didn’t go for my swim. I didn’t 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.

There were 14 relatives in the

room, lined up in silence. All the

siblings had been woken up and were standing staring at me.

Narrative drama

• Consulting room is a ‘stage’• The illness story is not told but enacted• The patient’s performance is the clue to

diagnosis

Cheryl Mattingly. ‘Healing Dramas and Clinical Plots: The Narrative Structure of Experience’.

New York: Cambridge University Press, 1998.

On examination by torchlight, the child was conscious and

co-operative, and had a typical

chicken pox rash.

She was post-pubescent and somewhat overweight. Her BP was 90/50 and pulse 100. She

was possibly overbreathing (we all were). She said she couldn’t

get up, or even sit up.

On direct questioning, she said “I just don’t feel well.

Maybe I’m a bit faint. No, I haven’t fainted or blacked

out but it’s muzzy and I feel quite scared that

something’s wrong.”

I 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.

I 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.

As I left the room, the father thanked me profusely for saving his daughter’s life.


We didn’t 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

Hospital 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

Primary 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

A 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

A note on storiesStory

= Actors+ Setting+ Plot+ Trouble+ Surprise

Kenneth Burke 1945“A grammar of motive”

[after Aristotle 528]

A 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

Conclusion: Stories and BayesGPs may be alert to subtle aspects of the

patient’s 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 don’t take the hunches of experienced GPs as “evidence” may be missing a trick

PS: The fascinoma paradox

• Doctors learn to manage common problems by discussing uncommon ones

• “When you hear hoofbeats, don’t think zebras”

Kathryn Montgomery Hunter. “Don’t think zebras”: uncertainty, interpretation, and the place of paradox in clinical education.

Theoretical Medicine 1996; 17: 225-241

Case 2:

A patient with depression

A story from general practice

• TG – a locum GP• Mrs Christine Morgan – a bank clerk

ACT ONE

TG Mrs Morgan?

CM [Enters the surgery. She is an unattractive woman of 54 but looks older. Her hair is pulled loosely into an untidy pony tail. Her skin is puffy and she wears no make up. She walks slowly, with the air of myxoedema about her (she doesn’t have it – someone has checked). She slumps into the patient’s chair and says nothing.]

TG What can I do for you?

CM [Tries to speak but finds herself tongue tied. The doctor makes eye contact and this triggers the flow of tears.]

[…] I’m sorry. I’m wasting your time.TG [reassuringly] No you’re not. This is what I’m paid for.

[…]

[From the notes, Mrs Morgan had a new diagnosis of depression about 6 weeks ago. She was given Prozac at that time. A week ago she was given a sick note.]

TG Is there anything particular you want to talk about?

CM […] I’ve… just got divorced after 30 years.

TG […] Mm. That’s quite a big thing.

CM [sniffs] Yeah.

TG Anything else?

CM […] There’s work. I can’t face it.

TG I’m not surprised. You’re not well enough to work, are you? What’s your job?

CM In a bank. I’m a cashier at Nat West. You deal with a lot of people. The customers are mostly nice, but… […]

TG I know. Dealing with the public. It’s a bit like this job. You’ve got to be feeling on the ball.

CM [smiles weakly] Yeah.

TG Dr Smith gave you a certificate for a week. Is that why you’ve come back?

CM [looking down guiltily] Mm. […] Look, I did try, I really tried. I’m not normally one for sick notes.

TG I can see that. I’ll sign you off for three more weeks, and I want to see you again before you go back to work.

CM [looks relieved] OK.

TG [writing certificate and placing it under blotter] That’s the sick note done. Now let’s talk about you.

CM […] It’s hard. Very hard.

TG Have you ever thought about committing suicide?

CM Mm. Lots.

TG And how would you do it?

CM Oh I never would. My little grandson – I wouldn’t do it to him. But I just think sometimes it would be nice just to stop being here. To go to sleep and not wake up.

TG It’s good that you still feel there’s someone to live for.

CM [crying] I’m supposed to be looking after him today.

TG [indicating certificate] Yes, but you’re ill, aren’t you?

CM Mm.

TG [suspecting non compliance since computer indicates no repeat prescriptions] What about the tablets?

CM So-so. I thought they’d work better than they did.

TG What else have you tried?

CM I talk to my friend, but you can’t keep dumping on them.

TG What about a counsellor? We’ve got one here – you could see her if you like. She’s called Trudy.

CM [unenthusiastic] Mm.

TG Sometimes it helps to talk. And whatever you say to Trudy is confidential. It doesn’t go on these notes.

CM Mm. Okay.

TG I’ll do a letter then. I’ll just say you’re depressed after a divorce and having trouble working. Then you can pick up from there. She’ll give you half an hour every time.

CM Mm.

TG And there’s one other thing. We do this thing called prescription for exercise. You know Copthall Sports centre?

CM Mm?

TG Well I can send a referral form and you can get to use all the facilities free.

CM Really? Swimming and everything?

TG Yes. If you have a medical condition that gets better with exercise – and depression does, often – you can have a “prescription” to have that. You get a full physical assessment too. And you meet people of course.

CM Yes, can I do that? I might be able to do something about my weight.

TG Fine. Pop in next week and pick up the pink form. You need to call the number on the top and speak to a man called Ali. You can keep the form at home until you feel you’re ready to ring him up.

CM Okay. I’ll do that.

TG Now, what are we going to do about your tablets?

CM Do you think I should be taking them?

TG Yes. They should help lift you enough to get these other things – like the counselling and the exercise – going.

CM Well, I’ll give them a go again. And I’ll come and see you in three weeks.

THE LETTERS

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.

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. I’m grateful to you for organising this.

ACT TWO

(3 weeks later)

TG Hello. How’ve you been?

CM [she looks dramatically better, in a clean, pressed blouse and a hint of lipstick]

Better. Definitely better. […] I’m still low – but not low low. Those tablets are better. I can do some normal things. Like I cleaned the windows yesterday.

TG Good grief. You can come and clean mine if you’re feeling like that!

CM [laughs] But today… today isn’t so good.

TG It will come and go.

CM Yes, I’m realising that.

TG What about work?

CM My manager came to see me at home. She’s been really good. They’re transferring me to another branch – down at X.

TG Oh, that tiny one on the corner?

CM Mm. There’s only seven staff. They keep saying it should be closed as there’s not enough business.

TG Well that’ll suit you fine for a bit, won’t it?

CM Yeah, I’m ready to give it a go.

TG And how’s the counselling?

CM [suddenly cries] Oh that. The young lass. I did do two sessions, but it seemed to upset me more.

TG It often does.

CM She kept wanting me to talk about the worst things. So I cancelled the last time.

TG Oh dear. What do you want to do about that?

CM Well I’m going back to work now aren’t I?

TG And the exercise?

CM I did ring them up. I’m seeing your man this afternoon actually. [Gets up and looks in mirror] I hope he’s going to tell me how to lose this weight.

TG I’m sure if you put that as one of your goals he’ll suggest something for it.

CM And you did say there would be other people there, doctor.

TG Yes, there will be loads of people there for weight loss. That’s the commonest thing people get referred for.

CM What, as bad as me? [indicating her tummy]

TG Oh, worse. And other problems – diabetes, blood pressure, that sort of thing. And some people will be there for depression too.

CM I’m so looking forward to meeting some new people. You see, all the friends I’ve got were sort of ‘our’ friends, and I want to get some that are just ‘my’ friends.

TG Okay then, so you want me to sign you back to work.

CM Yes, I was planning to go back Monday.

TG [writes certificate]. Fine. But I’d like to see you again in a month to see how you’re getting on.

CM Can I weigh myself on those scales?

TG Yes of course. We can check it again in a month’s time.

CM I am nervous, you know doctor.

TG It’s a big step. But you said you’re ready to have a go.

CM [takes deep breath as she is leaving] Mm. Bye doctor.

‘Textbook’ medical consultation

• Take a history • Examine the patient• Order investigations• Establish a differential diagnosis• Prescribe treatment • Refer if indicated

The 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 doctor’s role is partly to suggest

alternative ‘storylines’

A STORYLINE HYPOTHESIS

ACT ONE:A fragmented, inconsistent,unfinished, unhappy story

Her phys

ical

body

Her maritalrelationship

Her daughterand grandson Her friends

Her work Her leisureactivities

‘Dear Trudy’letter

‘Dear Ali’letter

STORYLINE OPTION:Psychiatric illness

STORYLINE OPTION:Shaping up and meeting people

ACT TWO:The ‘back to work’ plot

The 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

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.

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. I’m grateful to you for organising this.

Case 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.

Thank you for your attention

Handouts available from Marcia Rigby

[email protected]

Documents

Bayesian decision making in primary care – or how to stop people dying of chicken pox