Value of risk scores in the decision to palliate patients with ruptured abdominal aortic aneurysm

Abstract

Background: The aim of this study was to develop a 48-h mortality risk score, which included morphology data, for patients with ruptured abdominal aortic aneurysm presenting to an emergency department, and to assess its predictive accuracy and clinical effectiveness in triaging patients to immediate aneurysm repair, transfer or palliative care.

Methods: Data from patients in the IMPROVE (Immediate Management of the Patient With Ruptured Aneurysm: Open Versus Endovascular Repair) randomized trial were used to develop the risk score. Variables considered included age, sex, haemodynamic markers and aortic morphology. Backwards selection was used to identify relevant predictors. Predictive performance was assessed using calibration plots and the C-statistic. Validation of the newly developed and other previously published scores was conducted in four external populations. The net benefit of treating patients based on a risk threshold compared with treating none was quantified.

Results: Data from 536 patients in the IMPROVE trial were included. The final variables retained were age, sex, haemoglobin level, serum creatinine level, systolic BP, aortic neck length and angle, and acute myocardial ischaemia. The discrimination of the score for 48-h mortality in the IMPROVE data was reasonable (C-statistic 0·710, 95 per cent c.i. 0·659 to 0·760), but varied in external populations (from 0·652 to 0·761). The new score outperformed other published risk scores in some, but not all, populations. An 8 (95 per cent c.i. 5 to 11) per cent improvement in the C-statistic was estimated compared with using age alone.

Conclusion: The assessed risk scores did not have sufficient accuracy to enable potentially life-saving decisions to be made regarding intervention. Focus should therefore shift to offering repair to more patients and reducing non-intervention rates, while respecting the wishes of the patient and family.

Figure 1

Nomogram showing the IMPROVE risk score for 48‐h mortality for patients with ruptured abdominal aortic aneurysm. To use this nomogram, each of the patient's characteristics is assessed and the associated score read off (upper part). The total score is obtained by summing the scores from each of the individual characteristics, and the predicted 48‐h mortality risk can then be obtained (lower part)

Figure 2

Calibration plot for the IMPROVE risk score in the IMPROVE data set

Figure 3

Change in C‐statistic for four ruptured abdominal aortic aneurysm risk scores compared with the reference score using age alone as a risk factor. The change in C‐statistic was calculated in each cohort and for each risk score compared with using age alone. The changes were then pooled across cohorts. Changes in C‐statistic are shown with 95 per cent confidence intervals. The Vancouver score in the Amsterdam cohort contained only the effect of age because cardiac arrest and loss of consciousness were not available; therefore, no comparisons with an age‐alone model could be made

Figure 4

Decision curve showing the benefit of the IMPROVE risk score in helping make treatment decisions. The benefit to risk trade‐off inferred by a surgeon's chosen threshold probability of operating on a patient is shown on the x‐axis. For example, a surgeon who would treat patients with a mortality probability of 98 per cent or less quantifies the consequence of not operating when it would have been of benefit as 98 to 2, that is 49 times worse than the consequence of operating unnecessarily. The dotted line shows the net benefit (relative to treating no one) of treating everyone as a function of the benefit to risk trade‐off (chosen threshold). The dashed line shows the net benefit (relative to treating no one) of treating only those with a mortality risk below the chosen threshold