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Correspondence

Off-Pump Surgery, Cardiopulmonary Bypass, and Renal Dysfunction

^a Department of Anesthesiology, Pontificia Universidad Católica de Chile, Marcoleta 367, PO Box 114-D, Santiago RM, Chile
^b Santo Tomas University, Santiago, Chile

(Email: glema{at}med.puc.cl).

To the Editor:

The article by Di Mauro and colleagues [1] offers an interesting view of data from patients undergoing coronary surgical procedures and their impact on renal dysfunction, one of the complications of cardiac operations. The importance of preoperative renal dysfunction has already been described in cardiac surgery with cardiopulmonary bypass (CPB) [2]. We would like to add some comments to the discussion.

The overall results show that patients with abnormal preoperative renal dysfunction have an incidence of postoperative renal failure that similar between both techniques. We could hypothesized then, that the use of CPB may not be the main cause of this complication in these group of patients.

The authors ask why does even off-pump surgery impair renal dysfunction? There is no clear answer yet. The reduced plasma flow before CPB that has been shown in patients with normal and abnormal preoperative renal dysfunction [3, 4] could be also present during off-pump surgery. If this renal hemodynamic condition is left untreated, then hypoperfusion will remain until the patient is placed on CPB or throughout the operation during the off-pump procedure. Thus, in patients with abnormal preoperative renal function, changes in renal hemodynamic may be more relevant than CPB itself.

Another question is why does CPB cause a significant incidence of acute renal failure in patients with normal preoperative renal function? During off-pump operations, hemodynamic indicators are probably more closely monitored, most likely because there is no additional support from CPB. There is more control on fluid load, cardiac output tendencies, use of vasoactives drugs, and hematocrit; thus, renal plasma flow may improve throughout the complete procedure. During procedures with CPB, we tend to focus on CPB and less on other periods of the operation, specifically in the prebypass time. Our results in different cardiac populations (valvular, coronaries, and pediatrics) showed reduced effective renal plasma flow even before anesthesia and surgery. During those periods, patients could be susceptible to ischemic damage due to vasoconstriction and other superimposed factors, including low cardiac output, hypotension, low hematocrit, and vasoactive drugs, among others.

Some recent reports have used multivariable models analysis to isolate different predictors of renal dysfunction after cardiac surgery. The most important are age, sex, peripheral vascular disease, congestive heart failure, low ejection fractions, and preoperative renal dysfunction. Cardiopulmonary bypass time has also been isolated, but not CPB by itself [6].

According to the authors off-pump surgery has a renoprotective role. This is a very enthusiastic and speculative statement, without current literature support.

It should also be taken into consideration that the plasma creatinine concentration cutoff value of 1.5 mg/dL can be debated. There is ample evidence that the correlation with creatinine clearance when estimating glomerular filtration rate can be misleading, especially in the early stages of renal dysfunction [5].

	Acknowledgments

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The authors are supported by a grant from FONDECYT 1030645–2003.

	References

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1. Di Mauro M, Gagliardi M, Iaco AL, et al. Does off-pump coronary surgery reduce postoperative acute renal failure?. The importance of preoperative renal function. Ann Thorac Surg 2007;84:1496-1503.[Abstract/Free Full Text]
2. Aronson S, Blumentahl R. Perioperative renal dysfunction and cardiovascular anesthesia: concern and controversies J Cardiothorac Vasc Anesth 1998;12:567-586.[Medline]
3. Lema G, Meneses G, Urzua J, et al. Effects of extracorporeal circulation on renal function in coronary surgical patients Anesth Analg 1995;81:446-451.[Abstract]
4. Lema G, Urzua J, Jalil R, et al. Renal protection in patients undergoing cardiopulmonary bypass with preoperative abnormal renal function Anesth Analg 1998;86:3-8.[Abstract]
5. Bagshaw S, Bellomo R. Early diagnosis of acute kidney injury Curr Opin Crit Care 2007;13:638-644.[Medline]
6. Brown JR, Cochran RP, Leavitt BJ, et al. Multivariable prediction of renal insufficiency developing after cardiac surgery Circulation 2007;116:I-139-I-143.[Medline]

This article has been cited by other articles:

				M. Di Mauro and A. M. Calafiore Reply Ann. Thorac. Surg., July 1, 2008; 86(1): 350 - 350. [Full Text] [PDF]

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lema, G. Articles by Urzua, J. Search for Related Content PubMed PubMed Citation Articles by Lema, G. Articles by Urzua, J. Related Collections Coronary disease Related Article