Paediatric cardiac surgical mortality in England after Bristol: descriptive analysis of hospital episode statistics 1991-2002
http://www.100md.com
《英国医生杂志》
1 Dr Foster Unit at Imperial College London, Department of Epidemiology and Public Health, Imperial College School of Medicine, London W2 1PG
Correspondence to: P Aylin p.aylin@imperial.ac.uk
Abstract
One of the key issues for the Bristol inquiry1 was whether mortality statistics in Bristol were unusual compared with other specialist centres. Work commissioned by the inquiry examined hospital episode statistics data on cardiac surgery carried out in children at Bristol and other major centres in England.2 The main finding was that mortality in Bristol was about twice as high as in other centres from April 1991 to March 1995, for open operations in children aged under 1 year.
We report data on the performance of Bristol Royal Infirmary and that of the other major centres in England since the original research.
Methods
At Bristol, since the events that led to the inquiry1 and after considerable changes in the paediatric cardiac surgery service were introduced from 1995 onwards, mortality for open operations in children aged under 1 has fallen markedly, so that it is no longer an outlier. The national trend is towards a lower mortality, as reflected in the Society of Cardiothoracic Surgeons of Great Britain and Ireland's own published figures.6 Several factors might have contributed to the national reduction in mortality: chance, data quality, a reduction in the number of high risk cases or increase in the number of low risk cases operated on, or improved quality of care.
Data quality
Data quality is an important issue, although extensive comparisons with other data sources for the original research showed that hospital episode statistics data were of sufficient quality to be used for the analysis.2 4 A recent paper also showed that hospital episode statistics are suitable to be used to monitor deaths in hospital routinely.7 Missing data on outcomes could, however, bias results. We examined the sensitivity of our analyses to include admissions where the outcome is unknown, and it makes little difference to the overall pattern of mortality. The same centres have a significantly high mortality in epoch 3 (Bristol and Oxford), epoch 5 (Oxford and Leicester), and epoch 6 (Oxford), even after adjustment for procedure. Our evidence also shows that the quality of data, at least in terms of completeness, is improving.
Possible change in procedures or cases
A reduction in the number of high risk procedures or cases, or an increase in low risk ones, might reduce mortality; but no indication exists that any such systematic shifts have occurred. The numbers of procedures that are now carried out have changed: the reduction in repair of complete atrial ventricular septal defect may be due to increased antenatal diagnosis (with termination of pregnancy) of babies with Down's syndrome8; the reductions in secundum atrial septal defect procedures are probably due to the increasing number of patients undergoing percutaneous device closure by cardiologists; the reduction in truncus arteriosus may again be because of antenatal diagnosis and termination; cardiologists now carry out most pulmonary valve procedures by percutaneous intervention, and many of the children who would have had aortic valve replacements in the past are now having Ross procedures.9 We are not aware of any major changes in specific surgical technique except for the Nor-wood procedure for hypoplastic left heart syndrome, with a change in positioning of the shunt to provide pulmonary blood flow. This may also account for the increase in the number of Fontan operations, as all these children go on to have the procedure as the third stage. Adjustment for procedure between epochs still shows a marked reduction in mortality over time.
Open procedures in England have shifted towards being carried out exclusively by the 11 specialist centres; currently, practically no such procedures in children under 1 year are carried out outside these centres. Improvements in intensive care may also have contributed to the improvement in mortality, with an increasing number of appointments of dedicated intensivists, the introduction of more effective treatment of high pulmonary vascular resistance,10 and improved techniques of post operative mechanical ventilation.
Reasons for Oxford's death rates
Oxford alone had a significantly raised mortality in epoch 6. Although this was based on only 11 deaths, Oxford had a consistently raised mortality for all three epochs examined. It must be recognised, however, that in looking at 11 centres over three epochs, an element of multiple comparisons has to be considered. The consistency of Oxford's high mortality relative to other units over all three epochs makes this less of an issue, with a probability of this happening by chance alone of less than 0.0002. Even after adjustment for procedure and the inclusion in the analysis of all admissions with unknown outcomes recoded as alive, Oxford remains the only centre with significantly raised mortality for all three epochs. There may be differences in case mix that we have been unable to adjust for. We were not able, within hospital episode statistics, to examine and adjust for risk factors such as underlying heart function, lung function, kidney function, and other vascular conditions. Some concern has been expressed over cardiac surgery at Oxford in the past.11 The unit became aware in 1999-2000 of a possible downturn in their results with respect to transpositions of the great arteries and stopped carrying out these from May 2000. The unit's own more recent data indicate that mortality has fallen since then (J Morris, medical director, Oxford Radcliffe Hospitals NHS Trust, personal communication, 2 April 2004).
What is already known on this topic
The Bristol inquiry between 1991 and 1995 showed that Bristol had a much higher mortality for open operations in children aged under 1 year than other major centres
What this study adds
Recent hospital episode statistics data show that in Bristol mortality has fallen markedly after the changes there
Nationally, a gradual fall in mortality has become evident from the time data were first available
The Oxford Radcliffe Hospitals NHS Trust contributes to the central cardiac audit database,12 which collects more detailed information on case mix. An independent review of NHS paediatric and congenital cardiac services concluded that surgical results for all centres, based on only one year of data from the central cardiac audit database, all fall within a very narrow range and compare favourably with international results.13 A recent paper, again based on the database,14 found no detectable difference in 30 day or one year survival between any of the 13 UK tertiary centres for congenital heart disease; however, the analysis considered only one year of data (limiting statistical power), the centre comparisons were based on only six procedures, and no attempt was made to adjust for case mix. A reanalysis of our data for single years from 1991-2 to 1994-5 by using the same criteria indicates that the high mortality at Bristol would probably have been missed, reaching only borderline significance in one year, 1993-4 (11.7%, 99% confidence interval 4.7% to 22.7%) compared with a national average of 4.7% (99% confidence interval 3.3% to 6.3%).
Conclusion
Mortality at the Bristol Royal Infirmary has fallen markedly after the changes there, and a more gradual reduction in national mortality is evident from the time these data were first available. Improved quality of care may account for the decrease in mortality, through new technologies or improved perioperative and post-operative care, or both. Whatever the reasons for the reduction in mortality, this seems to be good news for patients and parents.
Additional figures and tables are on bmj.com
We thank Leslie Hamilton (consultant cardiac surgeon, Freeman Hospital, Newcastle upon Tyne) for his helpful comments on our draft and particularly for his advice on changing patterns of surgical and post-operative practice. We also thank Nicky Best (reader in statistics, Imperial College London) for her advice on statistical matters.
Contributors: PA and PE were involved in the original research. PA and BJ devised this follow up work. PA and AB carried out the data extract and analyses. PA and PE drafted the paper. All investigators contributed comments on drafts.
Competing interests: The work was funded by Dr Foster Limited. BJ served on the panel for the Bristol Royal Infirmary inquiry. PA was an expert witness for the inquiry. PE was on the statistical review panel for the inquiry.
References
The Bristol Royal Infirmary Inquiry. Learning from Bristol: the report of the public inquiry into children's heart surgery at the Bristol Royal Infirmary 1984-1995. Bristol Royal Infirmary Inquiry, July 2001. (CM 5207.) www.bristol-inquiry.org.uk/ (accessed 15 Sep 2004.)
Aylin P, Alves B, Best N, Cook A, Elliott P, Evans SJW, et al. Comparison of UK paediatric cardiac surgical performance by analysis of routinely collected data 1984-96: was Bristol an outlier? Lancet 2001;358: 181-87.
Aylin P, Alves B, Cook A, Bennett J, Bottle A, Best N, Catena B, Elliott P. Analysis of hospital episode statistics for the Bristol Royal Infirmary inquiry. London: Division Primary Care and Population Health Sciences, Imperial College London, 1999. www.bristol-inquiry.org.uk/Documents/hes_(Aylin).pdf (accessed 15 Sep 2004).
Spiegelhalter D, Evans SJW, Aylin P, Murray G. Overview of statistical evidence presented to the Bristol Royal Infirmary inquiry concerning the nature and outcomes of paediatric cardiac surgical services at Bristol relative to other specialist centres from 1984 to 1995. Bristol Royal Infirmary Inquiry, 2000. www.bristol-inquiry.org.uk/Documents/statistical overview report.pdf (Accessed 15 Sep 2004).
Marshall, EC, Spiegelhalter, DJ. League tables of in vitro fertilisation clinics: how confident can we be about the rankings? BMJ 1998;316: 1701-4.
Society of Cardiothoracic Surgeons of Great Britain and Ireland. Trends in surgery for congenital heart disease. London: SCTS, 2001. www.scts.org/doc/2123 (accessed 15 Sep 2004).
Poloniecki J, Charalambos S, Bland M, Jones P. Retrospective cohort study of false alarm rates associated with a series of heart operations: the case for hospital mortality monitoring groups. BMJ 2004;328: 375.
National Down Syndrome Cytogenetic Register. The National Down Syndrome Cytogenetic Register 2002 annual report. NDSCR, London: NDSCR, 2003. www.mds.qmw.ac.uk/wolfson/ndscr/NDCSRreport.pdf (accessed 15 Sep 2004).
Ross, DN. Replacement of the aortic and pulmonary valves with the pulmonary autograft. Lancet 1967;2: 956-958.
Goldman AP, Delius RE, Deanfield JE, de Leval MR, Sigston PE, Macrae DJ. Nitric oxide might reduce the need for extracorporeal support in children with critical postoperative pulmonary hypertension. Ann Thoracic Surg 1996;62: 750-5.
Bridge S, Dussek J, Macpherson W. Report of the external review into Oxford cardiac services. Issued by the South East Regional Office. Leeds: NHS Executive, 2000.
Central Cardiac Audit Database. www.ccad.org.uk/ccadweb.nsf (accessed 14 Sep 2004).
Department of Health. Report of the paediatric and congenital cardiac services review group. London: DoH, 2003. www.advisorybodies.doh.gov.uk/childcardiac/pccsreptdec03.pdf (accessed 15 Sep 2004).
Gibbs J, Monro J, Cunningham D, Rickards A. Survival after surgery or therapeutic catheterisation for congenital heart disease in children in the United Kingdom: analysis of the central cardiac audit database for 2000-1. BMJ 2004;328: 611-20.(Paul Aylin, clinical seni)
Correspondence to: P Aylin p.aylin@imperial.ac.uk
Abstract
One of the key issues for the Bristol inquiry1 was whether mortality statistics in Bristol were unusual compared with other specialist centres. Work commissioned by the inquiry examined hospital episode statistics data on cardiac surgery carried out in children at Bristol and other major centres in England.2 The main finding was that mortality in Bristol was about twice as high as in other centres from April 1991 to March 1995, for open operations in children aged under 1 year.
We report data on the performance of Bristol Royal Infirmary and that of the other major centres in England since the original research.
Methods
At Bristol, since the events that led to the inquiry1 and after considerable changes in the paediatric cardiac surgery service were introduced from 1995 onwards, mortality for open operations in children aged under 1 has fallen markedly, so that it is no longer an outlier. The national trend is towards a lower mortality, as reflected in the Society of Cardiothoracic Surgeons of Great Britain and Ireland's own published figures.6 Several factors might have contributed to the national reduction in mortality: chance, data quality, a reduction in the number of high risk cases or increase in the number of low risk cases operated on, or improved quality of care.
Data quality
Data quality is an important issue, although extensive comparisons with other data sources for the original research showed that hospital episode statistics data were of sufficient quality to be used for the analysis.2 4 A recent paper also showed that hospital episode statistics are suitable to be used to monitor deaths in hospital routinely.7 Missing data on outcomes could, however, bias results. We examined the sensitivity of our analyses to include admissions where the outcome is unknown, and it makes little difference to the overall pattern of mortality. The same centres have a significantly high mortality in epoch 3 (Bristol and Oxford), epoch 5 (Oxford and Leicester), and epoch 6 (Oxford), even after adjustment for procedure. Our evidence also shows that the quality of data, at least in terms of completeness, is improving.
Possible change in procedures or cases
A reduction in the number of high risk procedures or cases, or an increase in low risk ones, might reduce mortality; but no indication exists that any such systematic shifts have occurred. The numbers of procedures that are now carried out have changed: the reduction in repair of complete atrial ventricular septal defect may be due to increased antenatal diagnosis (with termination of pregnancy) of babies with Down's syndrome8; the reductions in secundum atrial septal defect procedures are probably due to the increasing number of patients undergoing percutaneous device closure by cardiologists; the reduction in truncus arteriosus may again be because of antenatal diagnosis and termination; cardiologists now carry out most pulmonary valve procedures by percutaneous intervention, and many of the children who would have had aortic valve replacements in the past are now having Ross procedures.9 We are not aware of any major changes in specific surgical technique except for the Nor-wood procedure for hypoplastic left heart syndrome, with a change in positioning of the shunt to provide pulmonary blood flow. This may also account for the increase in the number of Fontan operations, as all these children go on to have the procedure as the third stage. Adjustment for procedure between epochs still shows a marked reduction in mortality over time.
Open procedures in England have shifted towards being carried out exclusively by the 11 specialist centres; currently, practically no such procedures in children under 1 year are carried out outside these centres. Improvements in intensive care may also have contributed to the improvement in mortality, with an increasing number of appointments of dedicated intensivists, the introduction of more effective treatment of high pulmonary vascular resistance,10 and improved techniques of post operative mechanical ventilation.
Reasons for Oxford's death rates
Oxford alone had a significantly raised mortality in epoch 6. Although this was based on only 11 deaths, Oxford had a consistently raised mortality for all three epochs examined. It must be recognised, however, that in looking at 11 centres over three epochs, an element of multiple comparisons has to be considered. The consistency of Oxford's high mortality relative to other units over all three epochs makes this less of an issue, with a probability of this happening by chance alone of less than 0.0002. Even after adjustment for procedure and the inclusion in the analysis of all admissions with unknown outcomes recoded as alive, Oxford remains the only centre with significantly raised mortality for all three epochs. There may be differences in case mix that we have been unable to adjust for. We were not able, within hospital episode statistics, to examine and adjust for risk factors such as underlying heart function, lung function, kidney function, and other vascular conditions. Some concern has been expressed over cardiac surgery at Oxford in the past.11 The unit became aware in 1999-2000 of a possible downturn in their results with respect to transpositions of the great arteries and stopped carrying out these from May 2000. The unit's own more recent data indicate that mortality has fallen since then (J Morris, medical director, Oxford Radcliffe Hospitals NHS Trust, personal communication, 2 April 2004).
What is already known on this topic
The Bristol inquiry between 1991 and 1995 showed that Bristol had a much higher mortality for open operations in children aged under 1 year than other major centres
What this study adds
Recent hospital episode statistics data show that in Bristol mortality has fallen markedly after the changes there
Nationally, a gradual fall in mortality has become evident from the time data were first available
The Oxford Radcliffe Hospitals NHS Trust contributes to the central cardiac audit database,12 which collects more detailed information on case mix. An independent review of NHS paediatric and congenital cardiac services concluded that surgical results for all centres, based on only one year of data from the central cardiac audit database, all fall within a very narrow range and compare favourably with international results.13 A recent paper, again based on the database,14 found no detectable difference in 30 day or one year survival between any of the 13 UK tertiary centres for congenital heart disease; however, the analysis considered only one year of data (limiting statistical power), the centre comparisons were based on only six procedures, and no attempt was made to adjust for case mix. A reanalysis of our data for single years from 1991-2 to 1994-5 by using the same criteria indicates that the high mortality at Bristol would probably have been missed, reaching only borderline significance in one year, 1993-4 (11.7%, 99% confidence interval 4.7% to 22.7%) compared with a national average of 4.7% (99% confidence interval 3.3% to 6.3%).
Conclusion
Mortality at the Bristol Royal Infirmary has fallen markedly after the changes there, and a more gradual reduction in national mortality is evident from the time these data were first available. Improved quality of care may account for the decrease in mortality, through new technologies or improved perioperative and post-operative care, or both. Whatever the reasons for the reduction in mortality, this seems to be good news for patients and parents.
Additional figures and tables are on bmj.com
We thank Leslie Hamilton (consultant cardiac surgeon, Freeman Hospital, Newcastle upon Tyne) for his helpful comments on our draft and particularly for his advice on changing patterns of surgical and post-operative practice. We also thank Nicky Best (reader in statistics, Imperial College London) for her advice on statistical matters.
Contributors: PA and PE were involved in the original research. PA and BJ devised this follow up work. PA and AB carried out the data extract and analyses. PA and PE drafted the paper. All investigators contributed comments on drafts.
Competing interests: The work was funded by Dr Foster Limited. BJ served on the panel for the Bristol Royal Infirmary inquiry. PA was an expert witness for the inquiry. PE was on the statistical review panel for the inquiry.
References
The Bristol Royal Infirmary Inquiry. Learning from Bristol: the report of the public inquiry into children's heart surgery at the Bristol Royal Infirmary 1984-1995. Bristol Royal Infirmary Inquiry, July 2001. (CM 5207.) www.bristol-inquiry.org.uk/ (accessed 15 Sep 2004.)
Aylin P, Alves B, Best N, Cook A, Elliott P, Evans SJW, et al. Comparison of UK paediatric cardiac surgical performance by analysis of routinely collected data 1984-96: was Bristol an outlier? Lancet 2001;358: 181-87.
Aylin P, Alves B, Cook A, Bennett J, Bottle A, Best N, Catena B, Elliott P. Analysis of hospital episode statistics for the Bristol Royal Infirmary inquiry. London: Division Primary Care and Population Health Sciences, Imperial College London, 1999. www.bristol-inquiry.org.uk/Documents/hes_(Aylin).pdf (accessed 15 Sep 2004).
Spiegelhalter D, Evans SJW, Aylin P, Murray G. Overview of statistical evidence presented to the Bristol Royal Infirmary inquiry concerning the nature and outcomes of paediatric cardiac surgical services at Bristol relative to other specialist centres from 1984 to 1995. Bristol Royal Infirmary Inquiry, 2000. www.bristol-inquiry.org.uk/Documents/statistical overview report.pdf (Accessed 15 Sep 2004).
Marshall, EC, Spiegelhalter, DJ. League tables of in vitro fertilisation clinics: how confident can we be about the rankings? BMJ 1998;316: 1701-4.
Society of Cardiothoracic Surgeons of Great Britain and Ireland. Trends in surgery for congenital heart disease. London: SCTS, 2001. www.scts.org/doc/2123 (accessed 15 Sep 2004).
Poloniecki J, Charalambos S, Bland M, Jones P. Retrospective cohort study of false alarm rates associated with a series of heart operations: the case for hospital mortality monitoring groups. BMJ 2004;328: 375.
National Down Syndrome Cytogenetic Register. The National Down Syndrome Cytogenetic Register 2002 annual report. NDSCR, London: NDSCR, 2003. www.mds.qmw.ac.uk/wolfson/ndscr/NDCSRreport.pdf (accessed 15 Sep 2004).
Ross, DN. Replacement of the aortic and pulmonary valves with the pulmonary autograft. Lancet 1967;2: 956-958.
Goldman AP, Delius RE, Deanfield JE, de Leval MR, Sigston PE, Macrae DJ. Nitric oxide might reduce the need for extracorporeal support in children with critical postoperative pulmonary hypertension. Ann Thoracic Surg 1996;62: 750-5.
Bridge S, Dussek J, Macpherson W. Report of the external review into Oxford cardiac services. Issued by the South East Regional Office. Leeds: NHS Executive, 2000.
Central Cardiac Audit Database. www.ccad.org.uk/ccadweb.nsf (accessed 14 Sep 2004).
Department of Health. Report of the paediatric and congenital cardiac services review group. London: DoH, 2003. www.advisorybodies.doh.gov.uk/childcardiac/pccsreptdec03.pdf (accessed 15 Sep 2004).
Gibbs J, Monro J, Cunningham D, Rickards A. Survival after surgery or therapeutic catheterisation for congenital heart disease in children in the United Kingdom: analysis of the central cardiac audit database for 2000-1. BMJ 2004;328: 611-20.(Paul Aylin, clinical seni)