External validity of a mortality prediction model in patients after open abdominal aortic aneurysm repair using multi-level methodology.
OBJECTIVE
Evaluation of the prognostic ability of the APACHE-AAA model in an independent group of post-operative (open) Abdominal Aortic Aneurysm (AAA) patients.


METHODS
The model was applied to predict in-hospital mortality in 541 patients (325 elective and 216 emergencies; 489 from Oxford; 52 from Lewisham). Multi-level modelling was used to adjust for both the local structure and process of care and patient case-mix. Model performance was assessed using goodness-of-fit and subgroup analyses.


RESULTS
The model's predictive ability to discriminate between dead and alive patients was very good (ROC area=0.84). The model achieved a good fit across all strata of risk (Hosmer-Lemeshow C-test (8, N=476)=7.777, p=0.456) and in all subgroups. The model was able to rank the ICUs according to their performance independently of the patient case-mix.


CONCLUSIONS
The APACHE-AAA model accurately predicted in-hospital mortality in a population of patients independent of the one used to develop it, confirming its validity. The multi-level methodology employed has shown that patient outcome is not only a function of the patient case-mix but instead predictive models should also adjust for the individual hospital-related factors (structure and process of care).
Hadjianastassiou
V G
VG
Specialist Registrar, Department of Vascular Surgery, 1st Floor, North Wing, St. Thomas' Hospital, Lambeth Palace Road, London SE1 7EH, UK.
Tekkis
P P
PP
Athanasiou
T
T
Muktadir
A
A
Young
J D
JD
Hands
L J
LJ
D018806:APACHE; D000368:Aged; D000369:Aged, 80 and over; D017544:Aortic Aneurysm, Abdominal / Q000401:mortality* / Q000601:surgery; D016002:Discriminant Analysis; D004739:England / Q000453:epidemiology; D005260:Female; D017052:Hospital Mortality; D006801:Humans; D016015:Logistic Models; D008297:Male; D015233:Models, Statistical; D017063:Outcome Assessment, Health Care; D011379:Prognosis; D012372:ROC Curve; D018570:Risk Assessment; D012720:Severity of Illness Index