Acute kidney injury in renal transplant recipients undergoing cardiac surgery

Abstract

Background: Acute kidney injury (AKI) is a key risk factor for chronic kidney disease in the general population, but has not been investigated in detail among renal transplant recipients (RTRs). We investigated the incidence, severity and risk factors for AKI following cardiac surgery among RTRs compared with non-RTRs with otherwise similar clinical characteristics.

Methods: We conducted a retrospective cohort study of RTRs (n = 83) and non-RTRs (n = 83) who underwent cardiac surgery at two major academic medical centers. Non-RTRs were matched 1:1 to RTRs by age, preoperative (preop) estimated glomerular filtration rate and type of cardiac surgery. We defined AKI according to Kidney Disease: Improving Global Outcomes criteria.

Results: RTRs had a higher rate of AKI following cardiac surgery compared with non-RTRs [46% versus 28%; adjusted odds ratio 2.77 (95% confidence interval 1.36-5.64)]. Among RTRs, deceased donor (DD) versus living donor (LD) status, as well as higher versus lower preop calcineurin inhibitor (CNI) trough levels, were associated with higher rates of AKI (57% versus 33% among DD-RTRs versus LD-RTRs; P = 0.047; 73% versus 36% among RTRs with higher versus lower CNI trough levels, P = 0.02). The combination of both risk factors (DD status and higher CNI trough level) had an additive effect (88% AKI incidence among patients with both risk factors versus 25% incidence among RTRs with neither risk factor, P = 0.004).

Conclusions: RTRs have a higher risk of AKI following cardiac surgery compared with non-RTRs with otherwise similar characteristics. Among RTRs, DD-RTRs and those with higher preop CNI trough levels are at the highest risk.

Keywords: acute kidney injury; calcineurin inhibitor; cardiac surgery; kidney transplant; renal transplant.

Graphical abstract

FIGURE 1

Flow chart for cohort assembly. BWH, Brigham and Women’s Hospital; ICD-9/10, International Classification of Diseases-9th or 10th Revisions; MGH, Massachusetts General Hospital.

FIGURE 2

Incidence and severity of AKI in RTRs versus non-RTRs. (A) AKI event rates in RTRs versus non-RTRs. (B and C) Unadjusted and adjusted ORs for any AKI (B) and severe AKI (C). ORs depict the risk of AKI according to renal Tx status (RTR versus non-RTR), age (per 10 years), preop eGFR (per 10 mL/min/1.73 m²) and CPB time (per 10 min). ^aStage 2 or 3 AKI includes patients who required dialysis. ^bMultivariable models included the following variables: renal transplant (RTR versus non-RTR), age, preop eGFR and CPB time.

FIGURE 3

Subgroup analysis of transplant-specific risk factors in RTRs. AKI event rates are shown according to donor status (LD versus DD), prior rejection, prior renal Tx [defined as one or more failed renal allograft(s) prior to the current renal allograft] and time from Tx to cardiac surgery (A); CNI regimen (B); CNI trough level (C); CNI trough level combined with donor status (LD versus DD) (D); and native kidney disease etiology (E). The numbers above the bars represent the no. of events (%); the numbers below the bars represent the total no. of RTRs in each subgroup. ^aLow CNI trough level was defined as a preop tacro trough level ≤8 ng/mL or a CsA level ≤150 ng/mL; high CNI trough level was defined as a preop tacro trough level >8 ng/mL or a CsA level >150 ng/mL. The CNI trough level used was the most recent measurement within 72 h prior to cardiac surgery. Glom, glomerular disease; PKD, polycystic kidney disease.

FIGURE 4

Incidence and severity of AKI in DD- versus LD-RTRs. (A) AKI event rates in DD- versus LD-RTRs. (B and C) Unadjusted and adjusted ORs for any AKI (B) and severe AKI (C). ORs depict risk of AKI according to DD- versus LD-RTR, age (per 10 years), preoperative eGFR (per 10 mL/min/1.73 m²) and CPB time (per 10 min). ^aStage 2 or 3 AKI includes patients who required dialysis. ^bMultivariable models included the following variables: donor status (DD- versus LD-RTR), age, preoperative eGFR and CPB time.