How well does increased lactate differentiate between ITU survivors and nonsurvivors?

Several studies have shown that increased lactate correlates with outcome better than oxygen-derived variables. Despite this, lactate was not included in the APACHE II score because it was infrequently recorded.

This study aims to compare the ability of admission lactate, lactate at 24 hours and the APACHE II risk of death (ROD) score to discriminate between intensive care survivors and nonsurvivors. We also combined lactate at 24 hours with the APACHE ROD score to obtain the best discrimination values.

Two hundred and forty consecutive admissions to a nine-bed general intensive care unit (ITU) were prospectively investigated. Lactate values at admission and lactate at 24 hours were recorded. Each patient had the APACHE II ROD score calculated from data submitted to the Intensive Care National Audit and Research Centre. The ITU and hospital mortalities were analysed. The area under the receiver–operator characteristic (ROC) curve was calculated for each measure or combination of measures to test discrimination between survivors and nonsurvivors.

The overall intensive care and hospital mortalities were 29% and 39%, respectively. Both lactate on admission and lactate at 24 hours were significantly and strongly associated with intensive care mortality (P = 0.000 for both). Areas under the ROC curves show that both lactate measures discriminated between survivors and nonsurvivors (Table 1). The best discrimination is obtained by a combination of lactate at 24 hours and APACHE probability (obtained from a logistic regression).

Table 1

The 24 hour lactate values that give 50–75% mortalities are 1.5 and 3.6, respectively. Lactate at admission and at 24 hours are significantly strongly associated with intensive care mortality. Seventy-five per cent of patients with a lactate value of 3.6 at 24 hours will not survive.

Conclusions

The 24 hour lactate discriminates as well as the APACHE II ROD score between intensive care survivors and nonsurvivors, and is quicker and easier to obtain. Combining lactate into the APACHE II ROD score appears to improve the discriminatory power of this outcome prediction model. These data may help in discussions regarding patient prognoses on intensive care. In view of the strong association and discrimination between intensive care survivors and nonsurvivors and the widespread clinical use of lactate measurements, inclusion of the 24 hour lactate value should be included for future scoring systems.