Coronary surgery: Routine data provide no evidence of a correlation between volume of operations and the quality of outcomes

German health care data currently do not provide evidence that there is a statistical correlation between the volume of coronary surgery operations performed and the quality of outcomes. The risk in Germany of dying in hospital after the operation or of acquiring an infection does not depend on the number of cases treated by the respective hospital. This is the conclusion reached in the most recent final report by the Institute for Quality and Efficiency in Health Care (IQWiG), which the Cologne scientists presented on 16 August 2006. The IQWiG statisticians nevertheless emphasised that the reliability of these results is limited, as the quality of the available data is unclear.

The Institute was commissioned by the Federal Joint Committee ( Gemeinsamer Bundesausschuss, G-BA) to develop a statistical model that could be used to determine threshold values for establishing minimum volumes for coronary operations. For this purpose, staff members of the IQWiG Department of Medical Biometry evaluated health care data provided by the Federal Office for Quality Assurance (Bundesgeschäftstelle für Qualitätssicherung, BQS). Data were included from about 100 000 patients from 77 hospitals who had undergone isolated coronary surgery for the first time in 2003 and 2004; patients who had undergone emergency surgery were excluded. Experts in coronary surgery were nominated by the Federal Joint Committee, and they specified that the parameters for the quality of outcomes should be hospital mortality and the risk of infection after the operation. Process quality was also to be examined. The criteria for this were the use of the internal chest wall artery and the number of peripheral anastomoses per patient.

Calculation of threshold values not meaningful

On the basis of their multifactorial model calculation, the Cologne scientists concluded that there is no statistically significant correlation between the number of cases and either mortality or the risk of infection. It had originally been planned to calculate threshold values as a basis for the specification of minimum volumes, but this was clearly no longer possible. In addition, there was no statistically significant correlation between the two indicators of process quality and the volume of operations.

IQWiG emphasises that caution is necessary when interpreting the results of their model calculation. The lack of scientific evidence does not mean that absolutely no correlation exists. One reason for this is that the BQS data come from only 77 hospitals, which in each case performed the operation at least 166 times in the course of 2004. Theoretically it is quite possible that the volume of operations could influence hospital mortality, infection risk or other indicators in hospitals with lower case numbers - although such hospitals no longer exist in Germany.

Results are of limited reliability

According to the IQWiG project manager, Dr. Ralf Bender PD, "The quality of the currently available data is extremely uncertain, and the reliability of the results is therefore very limited.” The available data had been routinely collected and reported directly to the BQS by the hospitals. The BQS performed a control study on a sample in 2005. This showed that many of the complications noted in the medical records had evidently not been reported to the BQS. Conversely, many of the complications registered by the BQS could not be traced in the medical records. A specific assessment of the quality of the BQS data on coronary surgery is therefore not possible. In any case, the IQWiG experts consider that the available data do not provide sufficient scientific evidence that a regulation for minimum volumes could improve the quality of care. In the field of coronary surgery too, this is only possible with controlled intervention studies.

Background

Minimum volumes were first introduced in Germany with the Health Modernisation Act (Gesundheitsmodernisierungsgesetz [§137 Social Code Book V]). Doctors and hospitals may only perform specific operations if they do so with a specified frequency. In 2003, the self-administration partners agreed to define minimum volumes for five indications from 2004 onwards (liver, kidney, and stem cell transplantation, as well as complex operations on the oesophagus and pancreas).

In September 2004, the Federal Joint Committee also included coronary operations and total knee endoprostheses (knee TEP) in the so-called catalogue of plannable services, but did not specify numbers. The Federal Joint Committee commissioned IQWiG on 22 December 2004 to determine minimum volumes for coronary surgery; this commission was reformulated on 26 August 2005.

IQWiG presented the final report on knee TEP to the Federal Joint Committee on 5 December 2005; this was published on IQWIG's website on 6 February 2006. For this indication too, IQWiG concluded that threshold values to establish minimum volumes cannot be derived from the routine data available.

Contact: info@iqwig.de