Risk of Renal Failure After Cardiopulmonary Bypass Depends on Preop Renal Function and Pump Time

It is well known that prolonged cardiopulmonary bypass (CPB) time during cardiac surgery is associated with an increased risk of acute renal failure (ARF) postoperatively. However, exactly what amount of CPB time increases the risk is unclear. In addition, there is little information available about how the degree of a patient's preoperative renal impairment changes the risk.

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In The Journal of Thoracic and Cardiovascular Surgery, the research team led by Thoralf Sundt, MD, director of the Corrigan Minehan Heart Center and chief of the Division of Cardiac Surgery, and colleagues from Massachusetts General Hospital reports on a retrospective study of time on bypass versus renal failure to provide guidance to surgeons for real-time decision-making in the operating room and to facilitate discussions of risk with patients preoperatively.

The researchers reviewed records of 3,889 adults who underwent cardiac surgery utilizing CPB at Mass General between July 2011 and September 2017.

The primary outcome was postoperative development of ARF, defined as a three-fold increase in serum creatinine level, an absolute creatinine level >4 mg/dL or a new requirement for dialysis postoperatively. Postoperative ARF developed in 72 patients (2%), of whom 51 (1%) developed a new need for dialysis.

Of those 51 patients, 15 (29%) were discharged with eventual renal recovery, 15 (29%) had a permanent need for hemodialysis after discharge and 21 (42%) died without weaning from dialysis before discharge.

The researchers then stratified the results according to preoperative estimated glomerular filtration rate (eGFR):

• eGFR <30 mL/min/1.73 m² (n=100): 22% developed ARF, 16% needed new dialysis and 8% needed permanent hemodialysis
• eGFR 30 to 60 mL/min/1.73 m² (n=1015): 3% developed ARF, 2% needed new dialysis and 1% needed permanent hemodialysis
• eGFR >60 mL/min/ 1.73 m² (n=2774): <1% developed ARF

Within each eGFR category, the relationship between CPB time and risk of ARF was the same regardless of type of operation: isolated coronary artery bypass graft (CABG), isolated single valve, or CABG plus valve.

Risk Factors for Renal Failure

On multivariable regression analysis, independent risk factors for postoperative ARF were:

• Need for postoperative transfusion (odds ratio 11.94)
• Increasing preoperative creatinine (OR 4.21)
• Obesity (OR 3.03)
• Urgent/emergent cardiac surgery (OR 2.01)
• CPB time in 10-minute increments (OR 1.06)

Guidance for Planning Surgery

To help surgeons plan the conduct and extent of their procedures, the investigators developed graphs of the relationship between CPB time and the incidence of postoperative ARF, stratified by preoperative eGFR. These are available in the full journal article.

For example, among patients with good preoperative renal function (eGFR >60), there was only gradual incremental risk in the development of ARF for CPB time up to five hours. At one hour the predicted probability of ARF was 0.2% and at five hours it was 3%.

For patients with eGFR <30, however, the risk of ARF increased rapidly with longer CPB time. At one hour the predicted probability of ARF was 6% and at five hours it was 25%.

Other Advice for Surgeons

The researchers recommend that when a patient's preoperative eGFR is <30, surgeons should remain particularly aware of CPB time and think carefully before adding an adjunctive intervention to the primary procedure.

In addition, during shared decision-making about surgery, the surgeon should use knowledge of preoperative renal function and anticipated CPB duration to inform patients of their risk of postoperative ARF.

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