Minimal early mortality in CABG--simply a question of surgical quality?

BACKGROUND: The increasing number of risk scores and models for the evaluation of the early risk after cardiac surgery reflects the interest in 'calculating' the risk of adverse events. Different time intervals, but also different 'types' of death are generally accepted in the evaluation of early mortality. The aim of this study was to focus on the differences in the calculation of early mortality and to focus on their potentially misleading impact on risk stratification. METHODS: We investigated 7,436 patients who underwent coronary artery bypass grafting from June 30, 1988 through June 30, 2001. A follow-up was performed 180 days after operation (98.7 % complete). RESULTS: According to the definition of 30-day mortality to represent the total time interval between an intervention and the 30th postoperative day, the 30-day mortality was 5.92 % (n = 440 patients). Hospital mortality reflects the number of deaths from the day of intervention through the patient's individual discharge, independent of any fixed time interval. Hospital mortality was 5.86 % (n = 436 patients) in our patient group. 30-day hospital mortality requires the investigation of hospital mortality until the 30th postoperative day; in-hospital and general mortality after the 30th postoperative day remained excluded from the analysis; 30-day hospital mortality was 5.19 % (n = 386 patients). Assuming a maximum hospital stay of 5 days, hospital mortality would decrease to 2.64 % (n = 196 patients). CONCLUSIONS: 30-day mortality, hospital mortality and 30-day hospital mortality are used to determine early outcome. The present data indicate the vulnerability of non-standardized time intervals to discharge policy. However, both hospital mortality and 30-day hospital mortality are predominantly used in current risk scores and models. In view of the comparability and meaning of data, the methodology for the evaluation of early risk should be reconsidered.

Target, application, and interpretation of scores and alternative methods for risk assessment in cardiac surgery.

BACKGROUND: The more popular the use of different methods for risk adjustment becomes, the more often data are applied without any regard about the primary target and/or about important assumptions. Furthermore, risk adjustment is no longer restricted for quality assurance purposes, but became a "tool" of health policy. Few working groups currently use risk adjustment for the development of new therapeutic concepts. The aim of our study is to clarify possibilities and limitations of popular risk adjustment methods. PATIENTS AND METHODS: 4985 Patients underwent isolated CABG. Statistics was performed by calculating descriptive statistics, Parsonnet, and Higginsscores. Furthermore, the parametric, time-adjusted hazard function by Blackstone was used. RESULTS: Descriptive statistics allows intra-, and interinstitutional comparisons of single items to identify "outlying" results. Risk scores aim to predict preoperatively the risk category of the patient who undergoes cardiac surgery. However, since different scores are based on a score-specific combination of variables, and different definitions of the investigation interval, different results may occur, when different scores are calculated for a single patient. However, the use for example, of scores in patient groups allows description of changing risk structures. Most of the scores derive from univariate analyses and monophasic functions. However, survival curves are predominantly multiphasic and require a consideration of the time-dependency of "risk factors". DISCUSSION: An increasing number of patients with severe comorbidity undergoes cardiac surgery. To evaluate reliably present and futurous therapeutic options, risk adjustment is necessary. Since various tools for risk-adjustment are available, a serious discussion about reliability and application is necessary.