Effect of ionized serum calcium on outcomes in acute kidney injury needing renal replacement therapy: secondary analysis of the acute renal failure trial network study.

BACKGROUND: Hypocalcemia is very common in critically ill patients. While the effect of ionized calcium (iCa) on outcome is not well understood, manipulation of iCa in critically ill patients is a common practice. We analyzed all-cause mortality and several secondary outcomes in patients with acute kidney injury (AKI) by categories of serum iCa among participants in the Acute Renal Failure Trial Network (ATN) Study.

METHODS: This is a post hoc secondary analysis of the ATN Study which was not preplanned in the original trial. Risk of mortality and renal recovery by categories of iCa were compared using multiple fixed and adjusted time-varying Cox regression models. Multiple linear regression models were used to explore the impact of baseline iCa on days free from ICU and hospital.

RESULTS: A total of 685 patients were included in the analysis. Mean age was 60 (SD=15) years. There were 502 male patients (73.3%). Sixty-day all-cause mortality was 57.0%, 54.8%, and 54.4%, in patients with an iCa<1, 1-1.14, and ≥1.15 mmol/L, respectively (p=0.87). Mean of days free from ICU or hospital in all patients and the 28-day renal recovery in survivors to Day 28 were not significantly different by categories of iCa. The hazard for death in a fully adjusted time-varying Cox regression survival model was 1.7 (95% CI: 1.3-2.4) comparing iCa<1 to iCa≥1.15 mmol/L. No outcome was different for levels of iCa>1 mmol/L.

CONCLUSION: Severe hypocalcemia with iCa<1 mmol/L independently predicted mortality in patients with AKI needing renal replacement therapy.