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Publication

Is time on cardiopulmonary bypass during cardiac surgery associated with acute kidney injury requiring dialysis?

Elena MANCINI, Fabio CARAMELLI, Marco RANUCCI, Diego SANGIORGI,
Letizia Bacchi REGGIANI, Guido FRASCAROLI, Annalisa ZUCCHELLI,
Antonio BELLASI, Antonio SANTORO
Nephrology, Dialysis and Hypertension Unit, Policlinico S.Orsola-Malpighi, Bologna, Italy;
Cardiosurgery Intensive Care Unit, Policlinico S.Orsola-Malpighi,
Bologna, Italy; Department of Cardiothoracic-Vascular Anesthesia and Intensive Care, IRCCS Policlinico S. Donato, Milan, Italy; Institute of Cardiology, Policlinico S.Orsola-Malpighi, Bologna, Italy; Nephrology and Dialysis, Unit, Azienda Ospedaliera S. Anna,
Ospedale S. Anna, Como, Italy

The study explores the relationship between the duration of the cardiopulmonary bypass (CPB) and the occurrence of acute kidney injury after heart surgery.
CPB,  used to divert the blood from heart, leaving the surgeon able to operate on a bloodfree heart, is an unphysiological procedure, triggering a complex biological response (activation of the inflammatory cascade, coagulation, neurohormonal activation…). Hence, its duration has always been considered a factor directly favouring the appearance of kidney injury.

In the present study, with a large dataset (N=11.092) of subjects undergoing cardiac surgery, the time spent on CPB did not predict acute renal failure requiring dialysis (ARF-D) occurrence. Indeed, at the univariate analyses, time on CBP was associated with an increase in the ARF-D risk.  However, the  association between the time spent on CPB and the risk of developing ARF-D was not linear and lost its statistical significance after adjusting for confounders.

The results of our study indicate that in spite of the fact that the CPB is an unphysiological procedure, the duration of the procedure per se does not seem to be the main risk factor for kidney injury for a very large duration range. Instead, the complex interplay of comorbidity conditions, possibly coupled with the dramatic biological response to CPB, may account for renal function loss.

Yes, the main result was unexpected because in most of the studies previously published about acute kidney injury after heart surgery  the duration of CPB emerged as a causal factor linearly associated with the risk for ARF-D: the longer  the time on CPB, the higher the likelihood of developing ARF-D. 

Instead, we have demonstrated that over a broad range of CPB duration, the risk for ARF-D was stable, and only after long periods of CPB (i.e. over 120 mins) the risk for ARF-D acutely increased.  

We believe that these results should corroborate the notion that the preoperative risk assessment is far more important than time on CPB in the ARF-D risk prediction.

On the whole, the results suggest to the clinicians that the perspective of an open-heart surgery with long duration CPB should not be considered  in itself as a condition exposing the patient to a greater risk for ARF-D. A reasoned clinical  patient evaluation, including a thorough Nephrological assessment of pre-operative kidney function,  instead provides more information on this risk and should always be undertaken  in patients undergoing cardiac surgery  with CPB.

Considering the conflicting evidence available, our results should be confirmed by other studies and possibly in selected populations.
In particular, some aspects should be further evaluated:

• In which patients might the duration of CPB  have a critical role on the appearance of kidney injury? What parameters may be helpful in identifying them?

• How could the procedure of the CPB be modified in order to reduce the risk of kidney damage?