Does increased lactate discriminate between survivors and non-survivors after abdominal aortic aneurysm surgery?

Blood lactate levels have been correlated with outcome in sepsis,¹in shock of various causes¹ and following paediatric cardiacsurgery.² Lactate was not included in the APACHE II score becauseof practical difficulties with its determination and consequentinfrequent measurement in the early 1980s.³ Postoperative care following abdominal aortic or iliac aneurysm(AAA) surgery is the commonest reason for admission to UK intensivecare units (ICUs). These patients have a high hospital mortalityof 21.4% reported from the ICNARC Case Mix Programme.⁴ One hundredand forty-four consecutive patients admitted to ICU post-AAAsurgery were studied and four measures of lactate recorded fromthe first 24 h of admission (see Table 21). Four patients hadno values recorded. The Wilcoxon rank sum test was used to testfor a significant difference in each measure between survivorsand non-survivors. The area under the receiver operator characteristic(ROC) curve was calculated for each measure to test discriminationbetween survivors and non-survivors, where 1 represents perfectdiscrimination and 0.5 represents no discrimination. STATA 6.0for Windows 95 was used for all statistical tests. Increases in all measures of lactate were significantly associatedwith hospital mortality (probabilities from <0.0001 to 0.0035)(Table 21). The areas under the ROC curves show that all lactatemeasures discriminated between survivors and non-survivors.The 24-h lactate value provided both the strongest associationand the best discrimination. This may be because it is dependentnot only on the magnitude of physiological insult but also onthe adequacy of, and the response to postoperative treatment.In view of the positive correlation with mortality in this largegroup of critically ill patients and the now widespread clinicaluse of lactate measurements, inclusion of the 24-h lactate valueshould be considered for future scoring systems.