Initiation of renal replacement therapy in patients with acute kidney injury and severe lactic acidosis

Introduction

Both severe lactic acidosis (sLA) and acute kidney injury (AKI) with need for renal replacement therapy (RRT) are strong risk factors for mortality. The decision to initiate RRT in AKI patients with sLA is often a matter of dispute, and, because of lack of data, an anecdotal experience. The aim of the study was to describe the epidemiology of this specific cohort of ICU patients, and to evaluate specific risk factors for mortality.

Methods

A single-center, retrospective study on all adult ICU patients with AKI and sLA at initiation of RRT, during the 3-year period from August 2004 to July 2007. sLA was defined as serum lactate > 5 mmol/l. Data are presented as the proportion or median (interquartile range).

Results

Of 454 ICU patients with AKI-RRT, 89 (19.6%) had sLA at initiation of RRT. RRT was started 2.1 days (1.4, 3.1) after ICU admission. Continuous hemodialysis was used in 55.1%, slow low-efficiency daily dialysis in 11.2%, intermittent hemodialysis in 11.2%, and continuous venovenous hemofiltration (CVVH) in 22.5% of patients. The median age was 65.6 years (53.4, 72.8), 64% were male, and the APACHE II score at admission was 25 (19, 30). The majority were in the surgical ICU (67.4%), followed by the medical ICU (16.9%), cardiac surgery ICU (12.4%) and burn unit (3.4%). At the start of RRT, lactate was 13.1 mmol/l (7.6, 20.7), urea 0.92 g/dl (0.60, 1.22), creatinine 2.54 mg/dl (1.70, 3.47), pH 7.23 (7.11, 7.33), and HCO₃^- 16.6 (13.6, 21.0). ICU mortality was 80.9% (vs 56% for all RRT patients). The decrease of lactate was greater with hemodialysis compared with CVVH during the first 4 hours of RRT (23.9% vs 2.1%; P = 0.018). However, it was comparable after 24 hours (29.8% vs 38.1%; P = 0.267). Nonsurvivors were older (67.2 years vs 51.9 years; P = 0.003), had lower HCO₃^- (16.1 mmol/l vs 19.3 mmol/l; P = 0.039), higher urea (0.98 g/dl vs 0.57 g/dl; P < 0.001), and higher creatinine (2.6 mg/dl vs 1.8 mg/dl; P = 0.022). There was no difference in the serum lactate level between survivors and nonsurvivors. In addition, mortality was comparable in different ICUs, and in different RRT modalities. Finally, on multivariable analysis, only age and urea level were associated with mortality.

Conclusion

As much as one-fifth of ICU patients with AKI present with sLA at the start of RRT. This subgroup has a particularly high mortality. Serum lactate levels decreased faster with a dialysis modality compared with CVVH; however, this did not result in better outcomes. Surprisingly, lactate levels at the start of RRT were not predictive for mortality.