Associated factors and short-term mortality of early versus late acute kidney injury following on-pump cardiac surgery

Abstract

Objectives: Acute kidney injury (AKI) is common following cardiac surgery. The aim was to investigate the characteristics of AKI that occurred within 48 h and during 48 h to 7 days after cardiac surgery.

Methods: Patient data were extracted from Medical Information Mart for Intensive Care III database. AKI was defined according to the Kidney Disease Improving Global Outcomes guideline and divided into early (within 48 h) and late (during 48 h to 7 days) AKI. Multivariable logistic regression models were established to investigate risk factors for AKI. Cox proportional hazards model was used to analyse 90-day survival.

Results: AKI occurred in 51.2% (2741/5356) patients within the first 7 days following cardiac surgery, with the peak occurrence at 36-48 h. The incidence of early and late AKI was 41.9% and 9.2%, respectively. Patients with late AKI were older and had more comorbidities compared to early AKI patients. Risk factors associated with early AKI included age, body mass index, congestive heart failure and diabetes. While late AKI was related to atrial fibrillation, estimated glomerular filtration rate, sepsis, norepinephrine, mechanical ventilation and packed red blood cell transfusion. In Cox proportional model, both late and early AKIs were independently associated with 90-day mortality, and patients with early AKI had better survival than those with late AKI.

Conclusions: AKI that occurred earlier was distinguishable from AKI that occurred later after cardiac surgery. Time frame should be taken into consideration.

Keywords: Acute kidney injury; Cardiac surgery; Early AKI; Late AKI; Risk factors.

Figure 1:

Time distribution of acute kidney injury frequency following on-pump cardiac surgery.

Figure 2:

Variable importance plot of the random forest model. (A) Random forest model to predict early acute kidney injury versus no acute kidney injury. (B) Random forest model to predict late acute kidney injury versus no acute kidney injury. Max–min: difference between maximum and minimum value within one month prior to hospital admission. Max–min*: difference between maximum and minimum value during hospitalization.

Figure 3:

90-Day survival curve for patients undergoing cardiac surgery. Pairwise log-rank test was used to test difference in survival. Bonferroni correction were used to offset multiple comparisons. Early acute kidney injury versus no acute kidney injury: P < 0.001; late acute kidney injury versus no acute kidney injury: P < 0.001; early acute kidney injury versus late acute kidney injury: P < 0.001.