Table 2.

Effect of a restrictive versus liberal approach to red blood cell transfusion on AKI in patients undergoing cardiac surgery (n=4531)

AKI outcome definition	Number of Eventsa (%)		Risk Differenceb (95% CI)
	Restrictive (n=2251)	Liberal (n=2280)
Primary definition
AKIc	624 (27.7)	636 (27.9)	−0.2% (−2.8% to 2.4%)
Secondary definitions
AKI or deathd	636 (28.3)	662 (29.0)	−0.8% (−3.4% to 1.9%)
AKI for at least 2 de	363 (16.1)	354 (15.5)	0.6% (−1.5% to 2.7%)
Stage 2 (or higher) AKIf	166 (7.4)	150 (6.6)	0.8% (−0.7% to 2.3%)
Stage 3 AKIg	75 (3.3)	84 (3.7)	−0.4% (−1.4% to 0.7%)
Acute dialysis within 30 d of surgeryh	54 (2.4)	66 (2.9)	−0.5% (−1.4% to 0.4%)

^aAt least one postoperative serum creatinine assessment was available for 99.6% of patients. AKI was considered absent in 18 patients with no available assessments (five in the restrictive group and 13 in the liberal group); 16 of these 18 patients died within 1 d of surgery; none had dialysis within 30 d of surgery.

^bThe unadjusted absolute risk difference was calculated as the proportion of patients with AKI in the restrictive group minus the proportion in the liberal group. A two-sided 95% CI for the risk difference was calculated using the normal approximation for the difference in proportions.

^cThe primary outcome of the TRICS-III kidney substudy is perioperative AKI, defined as a postoperative increase in the serum creatinine concentration (from the preoperative value) of 0.3 mg/dl or more (≥26.5 μmol/L) within 48 h of surgery, or 50% or more within 7 d of surgery.

^dMet the primary definition of AKI or died within 5 d of surgery. This accounts for the potential effect of early deaths (38 of 2251 [1.7%] in the restrictive group; 52 of 2280 [2.3%] in the liberal group) on the ascertainment of AKI.

^eDefined as an increase in postoperative serum creatinine (from the preoperative value) of 0.3 mg/dl or more (≥26.5 μmol/L) within 48 h of surgery, or 50% or more within 7 d of surgery—on at least 2 d (not necessarily consecutive). This definition was examined because a longer duration of AKI is associated with worse outcomes.

^fDefined as an increase in postoperative serum creatinine of 100% or more from the preoperative value or an increase to an absolute value of 4.0 mg/dl or more (≥353.6 μmol/L) within 7 d of surgery, or receipt of dialysis within 30 d of surgery.

^gDefined as an increase in postoperative serum creatinine of 200% or more from the preoperative value or an increase to an absolute value of 4.0 mg/dl or more (≥353.6 μmol/L) within 7 d of surgery, or receipt of dialysis within 30 d of surgery.

^hThis definition was examined as an indication of severe AKI. In patients who received dialysis, the median increase in the serum creatinine concentration from the preoperative value to the peak postoperative value was 1.1 mg/dl (interquartile range, 0.6–1.9) (99 μmol/L [interquartile range, 52–169]).