A QUESTION OF NUMBERS

853 in

Letters

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the Editor

comparison of home

versus hospital treatment, Mather et series from South-West England and found a 28-day mortality of 15%. On the basis of the 32.6% 28-day male mortality for the Edinburgh dataand if we assume that the curve is approximately valid, the South-West England series must have been selected at a calculated median of 7 h after onset and are survivors from a group initially some 26% greater. The conclusions are likely to be of value in elucidation of pathogenic mechanisms and of the effects of interventions such as intensive coronary care. RAYMOND CARLISLE Department of Health and Social Security, A. FENTON LEWIS Hannibal House, London SE1 6TE a

al.4 followed

EXPONENTIAL CURVE OF TEMPORARY SURVIVAL AFTER MYOCARDIAL INFARCTION

SIR,-Deaths after myocardial infarction are usually early deaths. The precise form of the survival curve was obscured in one report on 998 fatal cases from Belfast (due to an irregular time scale) and the curve was not plotted in another report from Edinburgh.2 Both of these were precise studies on large numbers of subjects. We have re-investigated the published data by plotting % survivors (out of all ultimately fatal cases) against the logarithm of hours since onset (see figure). The Edinburgh data differed in that they refer to fatal cases as assessed at 28 days. There is consequently a downward displacement as compared with the Belfast data: and in both sets the male survival-rate runs lower than the female. The linear regressions are as follows, where y=% temporary survivors as defined above, and x=hours from onset: Males, Belfast: y=60.89-19.55 loglox Females, Belfast: y=64-80-19.13 log,ox Males, Edinburgh: y=51.48-18.56 loglox Females, Edinburgh: y=63-12-21.93 log,ox Correlation coefficients were within 1% of unity in all

cases.

Similar studies of other populations are required before we can say how generally valid the parameters may be. Nevertheless, as Smyllie et al. have indicated, any obvious departures from such a standard curve may be demonstrated. The data (from Doncaster) examined in their study are shown also in the figure. The upper points relate to survivors of 51 hospital admissions and the lower to 148 cases coming to post mortem. Both series are truncated in a temporal sense. Short survival ("sudden death") is over-represented in this post-mortem series, since they were all coroner’s cases. There are possible applications of such regression equations subject to the limitations of the sample from which they were calculated. One is to test the stage reached by a study population at the time of selection or of final assessment. For example 1 McNeilly, R. H., Pemberton, J. Br. med. J. 1968, iii, 139. 2. Armstrong, A., Duncan, B., Oliver, M. F., Julian, D. G., Donald, K. W., Fulton, M., Lutz, W., Morrison, S. L. Br. Heart J. 1972, 34, 67. 3. Smyllie, H. C., Taylor, M. P., Cuninghame-Green, R. A. Br. med. J. 1972,

A

QUESTION OF NUMBERS SIR,-Dr Loudon (April 3, p. 736) is quite right in pointing out that a large proportion of unnecessary follow-up appointments are for orthopaedic and fracture clinics. Discharging patients is very difficult tbr junior doctors. If the consultant does not get to see the "old patients", then numbers will get

larger and larger. For many years

HOURS

now

I have used two different methods for

keeping numbers reasonable and so ensuring proper attention for each person. Before starting each orthopaedic clinic I spend fifteen minutes looking through all the old patients’ case sheets for that day, noting what had happened at the previous appointment. I then decide whom I have to see myself either to review diagnosis and progress or to discharge them, and who will go to my assistant. During fracture clinics I sit next to the assistant at the same table, and we see patients simultaneously. In this way I can see and hear what he is doing and can give advice or take over a particular patient when necessary. 131 The Avenue, Leigh, Lancs

F. R. ZADIK

SIR,-Dr Loudon (April 3, p. 736) focuses on the large number of unnecessary outpatient follow-up appointments. In most clinics it is much easier to bring a patient back for a further visit than to discharge him. An outpatient visit is quick and easy for the doctor and requires no justification; it is a 4.

i, 34

a

AFTER

Mather,

H.

G., and others ibid. 1971, iii, 334.

ONSET

Temporary survivors as a percentage of their numbers at onset. Regression lines are for males as derived from the Belfast data’ (circles) and from the Edinburgh datal (squares). The points for females, somewhat higher, have been omitted for clarity. Crosses represent data for both sexes from the Doncaster study.’ The estimated median entry point of the male population followed up’ in South-West England is indicated by an asterisk.

854

negative decision. To discharge requires a more positive approach and usually a longer time in discussion with the pa-

(PRE)

AND AFTER CYTOGENETIC RESULTS BEFORE CATHETERISATION

tient and a more detailed letter to the G.P. To get over this and to help doctors in training rationalise their reasons for requiring a patient’s attendance I would suggest the reverse approach which I have used for some time in a variety of clinics. I believe that discharge should be regarded as the normal (negative decision) whereas a further appointment requires a positive reason or reasons which have to be recorded in the patient’s notes. Using this simple form of selfaudit I have considerably cut the number of patients attending on a chronic basis and as an added spin-off the notes are usually more informative. Of course, teaching, "stamp collecting", social reasons, or even a poor G.P. (usually classified as "social 2" in my notes) can be adequate reasons for another visit but they are at least considered ones. All patients thought to require long-term follow-up should be seen by the consultant on at least every third visit; this

continuity of care so lacking in many outpatient departments where junior doctors often change more frequently than the patients.

I

I

I

(POST) CARDIAC

I

ensures some

74 Blenheim Crescent, London W11

NOEL D. L. OLSEN

SIR,-Most general practitioners will support Dr Loudon’s about unnecessary follow-up appointments. Last

comments

month

patient came to ask for ambulance transport for her outpatient appointment. At the age of 74 she no longer felt able to cope with the journey by bus which would take the greater part of the day to get her there and back. Although I had seen her fairly often I was not aware that she was attending the hospital, but her notes revealed that she had had a hiatus hernia repaired 17 years previously. She said she had been attending ever since, although I had received no intermediate reports. With relief tinged with some apprehension she accepted my offer to cancel the appointment. The consultant agreed with my action whilst inviting me to refer her back again if necessary. Although I doubt if this will be needed it would of course be my duty if her condition required it. a

35 Bath

Road, Stonehouse, Gloucestershire GL10

2JF

KENNETH SOUTHGATE

RADIATION EXPOSURE DURING CARDIAC CATHETERISATION

SIR,-Some procedures used in diagnostic radiology inevitaresult in significant doses of radiation to the patient. One

bly

such technique is X-ray fluoroscopy associated with cardiac catheterisation where skin doses of over 100 rad have been recorded.’ We decided to try to measure the effective wholebody dose using chromosome aberration techniques. Because the ratio of the irradiated mass to total-body mass is highest in babies they would provide the best opportunity for detecting chromosome aberrations induced by radiation. The seven babies studied were aged 2 weeks to 16 months, and their previous radiation exposure consisted of not more than three chest radiographs. Patient 2 had also had a bariummeal examination for an anterior mediastinal mass. The posterior-anterior field from X rays generated at 60 kVp was approximately 12x 12 cm centred over the heart. The examinations lasted about 2 h with exposures given in fractions of 5-10 s, totalling about 15 min. In addition, each child was exposed to 90 kVp X rays for about 10 s to film the release of contrast medium. The skin doses over the field were measured with an array of sachets containing radiothermoluminescent lithium-borate powder. As shown in the table the skin doses did not exceed 10 rad and were much lower than had been 1.

Cough, J. H., Davis, R., Stacey, A. J. Br. J. Radiol. 1968, 41,

508.

The integral dose was estimated from the field area, skin dose, thickness of tissue in the field, and X-ray attenuation. These values were then converted into average wholebody dose using the weight of the patient. A 2ml blood-sample was obtained at the beginning of the procedure and another approximately 20 min after the final radiation exposure. Separated lymphocyte cultures were set up using a routine technique, and the resulting metaphase spreads of chromosomes were examined for dicentric, acentric, and centric ring aberrations. The aberration yields in 500 cells scored in blood-samples taken before and after examination are given in the table. The techniques for cell culture and the criteria used in the analysis of the aberrations have been described elsewhere.2 Most damage was found in patient 1 who also received the highest radiation dose. However, in general there is little correlation between the aberration yields and the whole-body dose. Combination of the excess number of aberrations post-treatment relative to pre-treatment gives 9 dicentrics, 9 acentrics, and 3 centric rings in 3500 cells. From the dose-response curves for X-rays produced in this laboratory by in-vitro irradiation of adult blood, the yield of 9 dicentrics in 3500 cells indicates a dose of 5 rad or, taking into account all the aberrations, 6 rad.3 These biological dose estimates are about an order of magnitude above the calculated average whole-body dose to these patients. There are two possible explanations for this high biological dose estimate; firstly, there may be a high concentration of lymphocytes in the exposure field relative to the rest of the body because the field includes the heart, the major blood-vessels, and parts of the thoracic lymph ducts. However, in adults T lymphocytes exchange rapidly between the peripheral blood and the tissues with a mean residence-time in the blood of about 5 min, and only 3% of the total number of lymphocytes in the body are in the circulation at any one time/ If these values are applicable to babies this large extracirculatory reservoir of lymphocytes would tend to mask any selective irradiation due to the high blood content of the field. The second possibility is that the radiosensitivity of the chromosomes in lymphocytes from small children is greater than that in adults, Most in-vitro experiments have been made with adult blood but Sasaki and Tonomura irradiated blood taken from donors with ages from 1 month to 40 years and showed a significantly increased yield in lymphocytes from children less than 1 year old.’ In samples from babies between 1 and 2 months old the aberration yield was approximately double that for adults. Our

expected.

2.

Purrott, R. J., Lloyd, D. C. National Radiological Protection Board report no. 2, 1972. 3. Lloyd, D. C., Purrott, R. J., Dolphin, G. W., Bolton, D., Edwards, A A., Corp. M. J. Int. J. Radiat. Biol. 1975, 28, 75. 4. Sharpe, H. B. A., Dolphin, G. W., Dawson, K. B., Field, E. O. Cell Tissue 5.

Kinet. 1968, 1, 263. Sasaki, M. S., Tonomura, A. Jap. J. hum. Genet. 1969,14, 81.