Simulations of the effects of scheduled abdominal aortic aneurysm repair on survival

Abstract

SummaryI simulated survival with and without scheduled repair of abdominal aortic aneurysms with different diameters in different populations. The results imply that scheduled repair should be determined by the combination of a patient's monthly mortality hazard and aneurysm diameter. The median survival of some patients will be extended by the scheduled repair of aneurysms smaller than 55 mm, whereas the median survival of other patients will be curtailed by repair of any aneurysm. The results also suggest that, on average, surveillance is futile: the effect of scheduled aneurysm repair on an individual's median survival did not change but the cohort effect diminished as patients died during surveillance. The results of the UK Small Aneurysm Study were reproduced in simulation and are compatible with the repair of aneurysms smaller than 55 mm diameter. Epidemiological simulations suggest that past randomised controlled trials underestimate the effect of aneurysm repair today.

Dispassionate indicator or evil curse: are some scoring systems for predicting postoperative mortality lethal?

“…Some methods probably work better for some patient populations than others. Figure 2 The mortality predicted by SORT vs that predicted by CR-POSSUM for the cohort of 11 patients analysed by Carlisle [1]. Note the same patient is predicted different mortalities, and this also applies if the other systems are examined.…”

“…when we look across from any point on the y-axis, we are not looking at the same patient). Moreover, as Carlisle concludes in his editorial [1], the middle two methods (UK audit tool and Torbay model) yield actual mortality data that better fit the data of de Buck van Overstraeten et al [2]. The shock effect is created by the outlier scoring systems.…”

Discounting risk prediction models – a reply

“…I have used a calculator, which modifies general population survival, to generate accurate projected survival after repair of intact abdominal aneurysms, after cardiac surgery and after resection of colorectal cancer (I win) [2][3][4][5][6]. I have used a calculator, which modifies general population survival, to generate accurate projected survival after repair of intact abdominal aneurysms, after cardiac surgery and after resection of colorectal cancer (I win) [2][3][4][5][6].…”

“…We disagree on whether average population survival data can be modified to accurately project years of postoperative survival: I say that it can, Drs Wong and Bedford say that it cannot. I have used a calculator, which modifies general population survival, to generate accurate projected survival after repair of intact abdominal aneurysms, after cardiac surgery and after resection of colorectal cancer (I win) [2][3][4][5][6]. The same calculator shows that survival after oesophagectomy is very different to that for a matched general population whose mortality is Figure 1 Kaplan-Meier survival curves (95%CI) after admission to Torbay intensive care unit, stratified by whether admission was medical or followed surgery, elective or emergency.…”

Too much blood pressure?

“…(I would like to emphasise here the importance of absolute risk: anaesthetists should gauge their concern for a patient with raised blood pressure by the calculated mortality rate or rate of cardiovascular events for that patient and not by the blood pressure measurement per se). For these simulations I have used a calculator that I developed, which is described elsewhere . In both cohorts, blood pressure is lowered three months after pre‐operative assessment.…”