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LETTER TO THE EDITOR |
Department of Anestesia, Facultad de Medicina, Pontificia Universidad Católica de Chile. Marcoleta 367, Santiago, Chile
E-mail: glema{at}med.puc.cl, Department of Anestesia, Facultad de Medicina, Pontificia Universidad Católica de Chile, Marcoleta 367, Santiago, Chile.
The manuscript by Joanna SM Ooi MMed deserves a careful look at the numbers and conclusions drawn by the authors (1).
Renal failure continues to be a major problem after cardiac surgery. It is well known and extensively reported in the literature that preoperative renal dysfunction is an independent factor of postoperative renal failure.
It has been suggested in the literature that the use of cardiopulmonary bypass (CPB) may be responsible for this and other complications. This statement has been quoted by many authors, without basic or clinical research data to support these conclusions for adults an children undergoing surgery with CPB.
In the introduction, the authors implicate the use of CPB as one of the main causes of postoperative renal failure. "Inadequate or nonpulsatile renal perfusion, macro-and microembolic loads on the renal vasculature, and the inflammatory response to CPB have been implicated as potential etiologic factors for postoperative renal dysfunction and renal failure". This statement could be misleading. There are a great numbers of clinical conditions that can deteriorate the function of the kidneys, including: low hematocrit, low cardiac output, vasoconstriction associated to inotropic support, bleeding, blood transfusions, haemodilution, among others.
Studies from our group showed that renal plasma flow as well as glomerular filtration rate is well preserved during CPB in children and adults with normal and abnormal preoperative renal dysfunction (2).
Many drugs or techniques have been extensively used in clinical practice in order to reduce renal damage. Results so far are discouraged.
Off-pump surgery has been used extensively in different clinical conditions. In patients with abnormal preoperative renal dysfunction this technique has been advocated as being beneficial, however there are some studies showing that in patients with preoperative renal dysfunction the incidence of postoperative renal failure is similar between on and off pump surgery (3).
Data and conclusion from this study are difficult to support:
Although acknowledged by the authors, the sample size is too small. To obtain significant differences in a clinical condition such as this, you would need at least 100 patients in both groups. Moreover if randomization was not done, a new variable has to be considered in the results, which is the expertise of the team, specifically the surgeons. It is not clear, how patients were included in the groups, maybe the sicker patients had on pump surgery? We don’t know.
Results show that there is no change in creatinine clearance (CrCl) in both groups throughout surgery and in the postoperative period. A significant reduction of CrCl was found in the on-pump group during the postoperative period when compared with basal values, however the clinical significance of those changes is at the most weak. Changes occurred mostly in day two. This is important due to the fact that as mentioned before, changes occurring in the perioperative period are probably more relevant to produce renal damage than CPB. CrCl at the end of the study is similar to baselines numbers.
The author’s state in the conclusions that " . . . our finding that Of CAB provides better renal protection than on-pump CABG in . . . " but due to the weakness of the protocol, this sentence should be considered just speculative. "Renal protection" is difficult to define thus difficult to implement.
REFERENCES
Asian Cardiovasc Thorac Ann 2009;
17:440-441
© 2009 by SAGE Publications
DOI: 10.1177/0218492309343860
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