Materials and methodsThe data collection and the data analysis for this study are part of ongoing de-identified data auditing processes across the participating hospitals, which have all waived the need for informed selleck chemicals consent. The Austin Hospital Ethics Committee approved the study.Study population and data sourcesWe conducted this study as a four-centre retrospective investigation of a prospectively gathered intensive care database. Four Australian university teaching hospital intensive care units enrolled patients in this study. We included all patients admitted to these ICUs from January 2000 to October 2004.The blood lactate concentration data used for this study were stored and retrieved electronically.

We obtained age, sex, use of mechanical ventilation, reason for ICU admission, surgical and non-surgical divided into (trauma, cardiac/vascular, gastrointestinal tract, neurological and thoracic/respiratory diseases), and Acute Physiology and Chronic Health Evaluation (APACHE) II score [15] from the electronic data repositories of each ICU, using prospectively collected data as part of a continuing data collection by the Australian and New Zealand Intensive Care Society – Centre for Outcome and Resources Evaluation (ANZICS-CORE). We coded admission diagnosis by APACHE III system used by the ANZICS-CORE – Adult Patient Database [16].All patients had initial arterial lactate and blood gas measured by blood gas analyser (Rapilab, Bayer Australia, Sydney, NSW, Australia, upper normal limit 2.00 mmol.L-1) at the time of admission to the ICU.

The timing of repeat measurements was at the discretion of the managing critical care team. All subsequent blood lactate measurements were performed using the same blood-gas analyzer in each hospital. A normal (within reference) lactate was defined as a concentration between 0.00 and 2.00 mmol.L-1 [13]. Laboratories in the participating hospitals comply with standards of the National Association of Testing Authorities [17] and the Royal College of Pathologists of Australasia [18].Statistical AnalysisWe Drug_discovery used the ICU admission (LacADM) and maximal (LacMAX) blood lactate concentrations to indicate the admission and highest value recorded while in the ICU. We first assessed blood lactate concentration in all patients and second, in those patients whose ICU admission (LacADM), and maximal (LacMAX) blood lactate concentrations never exceeded the normal reference range (that is, < 2 mmol.L-1). In addition, to avoid the potential effect of surveillance bias due to the increased blood lactate monitoring in more severely ill patients, we calculated the time-weighted lactate concentration (LacTW).