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Re: Cardiac surgery, cardiopulmonary bypass and preoperative renal dysfunction.
- Berthus G Loef, R. Henning, G. Navis, A. Rankin, W van Oeveren, T.Ebels, A.Epema (29 June 2008)
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Re: Renal oxygen delivery during cardiopulmonary bypass
- Berthus G Loef, R. Henning, G. Navis, A.Rankin, W. van Oeveren, T.Ebels, A. Epema (29 June 2008)
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Renal oxygen delivery during cardiopulmonary bypass
- David J Morrice (19 June 2008)
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Cardiac surgery, cardiopulmonary bypass and preoperative renal dysfunction.
- Guillermo Lema, Jorge Urzua, Roberto Jalil, Roberto Canessa (28 May 2008)
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Berthus G Loef , R. Henning, G. Navis, A. Rankin, W van Oeveren, T.Ebels, A.Epema
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Editor--- We thank Dr Lema and colleagues for their comments and ideas on the subject discussed. Their remarks concern both the absence of change in glomerular filtration rate (GFR) and the mechanism of change in filtration fraction (FF). With respect to GFR, unfortunately, only a limited number of small studies evaluating the effect of cardiac surgery with cardiopulmonary bypass on renal function using gold standard techniques have been reported. However, recently Witczak et al. studied the effect of nifedipine infusion on glomerular filtration rate (GFR) in patients (n=20) with impaired renal function undergoing cardiopulmonary bypass surgery.1 GFR was measured as the plasma clearance of 51chromium- ethylenediaminetetraacetic acid preoperatively and 48 h postoperatively and creatinine clearance was measured preoperatively and 0–4, 20–24 and 44–48 h postoperatively. The authors found no statistically significant change in the GFR or in creatinine clearance over time within or between groups. This study supports our observation that modern techniques for CPB management are able to protect renal function in patients with preoperative renal dysfunction.2,3 With respect to FF, we agree that interpretation of our data as to the cause of the increased filtration fraction (FF) following CPB remains speculative. In patients with normal renal function (plasma creatinine <1.5 mg/dL) undergoing coronary surgery, Lema et al. found an abnormally elevated FF preoperatively, a significant decrease during bypass, which returned to abnormally elevated baseline values one hour postoperatively FF.4 The increased FF we observed on day 7 postoperatively may thus represent an extension of the suggested vasoconstrictive state, with unknown consequences to renal function. However, it may also represent a structural remodeling of the vasculature, particularly in our patients suffering from modest impairment of renal function. Until now, renal function studies in cardiac surgical patients are limited to the hospital period and no long-term follow up is available. Renal function measurements in cohorts of cardiac surgical patients should extend the hospital period to provide insight in the mechanism of changes in renal parameters, and the possible bearings on the long-term effects of cardiac surgery with CPB on renal function. References 1. Witczak BJ, Hartmann A, Geiran OR, Bugge JF. Renal function after cardiopulmonary bypass surgery in patients with impaired renal function. A randomized study of the effect of nifedipine. Eur J Anaesthesiol 2008; 25:319-325 2.Lema G, Urzua J, Jalil R, et al. Renal protection in patients undergoing cardiopulmonary bypass with preoperative abnormal renal function. Anest Analg 1998;86:3-8. 3.Loef BG, Henning RH, Navis GJ, et al. Changes in glomerular filtration rate after cardiac surgery with cardiopulmonary bypass in patients with mild preoperative renal dysfunction. Br J Anaesth 2008; 100: 759-64 4.Lema G, Meneses G, Urzua J, et al. Effects of extracorporeal circulation on renal function in coronary surgical patients. Anesth Analg 1995;81:446- 51 Conflict of Interest:None declared |
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Berthus G Loef , R. Henning, G. Navis, A.Rankin, W. van Oeveren, T.Ebels, A. Epema
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Editor. We thank Dr. Morrice for addressing several issues that may explain the maintenance of renal function following CPB in our patient population. At our institution, pump flow is routinely maintained at a fixed level during mild hypothermia. Further, haematocrit levels during CPB are targeted at 20-25%; if necessary because of hemodilution, blood donation is instituted at the start of bypass. Because of our procedure, we agree with Dr Morrice that the fixed pump flow during CPB, providing increased DO2, may offer an explanation for the protection of renal function. However, our study was not designed to establish effects of oxygen delivery on perioperative renal function and the data requested are unavailable. Indeed, it would be of interest in the future to have a similar study conducted to evaluate the influence of oxygen delivery on renal function during cardiopulmonary bypass. In view of the ease of recruiting patients and the duration of the trial, it would be worthwhile to explore whether such a study would benefit from the use of sensitive markers for glomerular and tubular function.1 References 1.Loef BG, Henning RH, Epema AH, et al. Effect of dexamethasone on perioperative renal function impairment during cardiac surgery with cardiopulmonary bypass. Br J Anaesth 2004; 93:793-798 Conflict of Interest:None declared |
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David J Morrice
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Editor, I read with interest the study by Loef et Al (BJA June 2008), which investigated the effect on renal function of Cardiopulmonary bypass (CPB) in selected patients undergoing cardiac surgery. It is reassuring to discover that there was no significant evidence of a deterioration in Glomerular filtration rate (GFR). A deleterious patient or treatment characteristic could theoretically have caused a significantly lower GFR post operatively and there was an attempt to select out such patients. I am nevertheless concerned for several reasons about the omission of data on Oxygen delivery/DO2 (eg.Haemoglobin level, Pump flow) before, and at the time of CPB. Firstly, the medullary zone of the kidneys has for some time been assumed to be prone to hypoperfusion because it is an area of high metabolic rate (“on the verge of hypoxia”). Recent research on rats has suggested that this may be more specifically the Juxta medullary zone1. Reduced oxygen delivery (calculated by the oxygen delivery equation equation) therefore gives a physiological basis for potential renal damage. Low intraoperative haematocrit occurs as a result of blood loss, haemodilution and low starting Haemoglobin and directly affects oxygen delivery during cardiac surgery. Ranucci et al2 demonstrated that lowered Haematocrit is linked to development of renal dysfunction. Blood transfusion data has not been declared but red cell transfusion has also been identified as a risk factor for adverse outcome after cardiac surgery3. In addition, Karkouti et al4 identified that a preoperative haemoglobin level below 9g/dL is an independent risk factor for adverse outcome after cardiac surgery. I would also like to comment that whilst Pump flow is stated at 2.2litres/min-1/kg-1 in the paper, in our department it is customary to reduce this by approximately 5% per degree centigrade of cooling according to mixed venous oxygen estimation and I wonder if this was the case in this study. Ranucci has commented that increasing pump flow when haematocrit falls can counteract the effect of reduced O2 carrying capacity, so if pump flow was not reduced I wonder if this has had a beneficial effect. It certainly would be of interest in the future to have a similarly conducted study which includes a group with anaemia to permit comparison of outcome, as anaemic patients do present for cardiac surgery relatively commonly. Dr David Morrice, Consultant anaesthetist, Heart and Lung Building, Newcross Hospital, Wolverhampton. 01902 694357 david_morrice@mac.com (1.)T.Whitehouse M.Stotz V.Taylor R. Stidwill M.Singer Tissue oxygen and hemodynamics in renal medulla, cortex & cortico -medullary junction during hemorrhage-reperfusion Articles in PresS. Am J Physiol Renal Physiol (March 8, 2006). doi:10.1152/ajprenal.00475.2005 (2) M. Ranucci, F. Romitti, G. Isgro, M. Cotza, S. Brozzi, A. Boncilli, and A. Ditta Oxygen Delivery During Cardiopulmonary Bypass and Acute Renal Failure After Coronary Operations Ann. Thorac. Surg., December 1, 2005; 80(6): 2213 - 2220. (3) Effect of peri-operative red blood cell transfusion on 30-day and 1-year mortality following coronary artery bypass surgery Manoj Kuduvalli, Aung Y. Oo , Nick Newall, Antony D. Grayson, Mark Jackson, Michael J. Desmond, Brian M. Fabri and Abbas Rashid Eur J Cardiothorac Surg 2005;27:592-598 (4) K. Karkouti, D. N. Wijeysundera, W. S. Beattie, and for the Reducing Bleeding in Cardiac Surgery (RBC) Risk Associated With Preoperative Anemia in Cardiac Surgery: A Multicenter Cohort Study Circulation, January 29, 2008; 117(4): 478 - 484. Conflict of Interest:None |
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Guillermo Lema, MD Pontificia Universidad Católica de Chile, Jorge Urzua, Roberto Jalil, Roberto Canessa
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To the Editor: I have read with interest the paper by B. G. Loef et al.1 This is a very complex study and adds new information to the discussion of the subject. Authors should be congratulated for their work. I would like to add some comments and ideas to the discussion. Our group published in 1998 a study on elective coronary patients, with abnormal preoperative renal function undergoing surgery with cardiopulmonary bypass (CPB), 2 using “gold standard” techniques to measure glomerular filtration rate (GFR) and effective renal plasma flow (ERPF). Further studies by our group have been carried out in children and valvular patients undergoing surgery with CPB, with similar methodology. Our study, however, was intended to focus only in the preoperative period. It is extremely difficult to study patients in the postoperative period of cardiac surgery, due to many variables involved in this period such as: changes in haemodinamic variables, use of vasoactive drugs, changes in hematocrit, bleeding, among other. Thus, the meaning of the results presented by Loef et al, are speculative. It is interesting that GFR remains within normal values in patients with preoperative renal dysfunction during both studies, 1, 2 suggesting that modern techniques for CPB management are able to protect renal function. It also refutes earlier work, suggesting that CPB reduced the GFR in all patients. ERPF increased during CPB in all our earlier studies in coronary patients. In recent studies on valvular and paediatric patients, ERPF remains within baseline values throughout the study. This difference could be related to new strategies during CPB: higher perfusion pressures, vasopressor drugs, and higher hematocrit, among other. I would disagree with the authors regarding the explanation for changes found in filtration fraction (FF). We showed in our work that during CPB (hypothermia) FF decreased. FF has been use and an index of vasodilatation or vasoconstriction of the afferent arteriole. The reduction of FF most likely represents a vasodilatation state, due to hypothermia, low viscosity or the release of vasoactive endothelial factors. A high FF in the postoperative period could represent a vasconstrictive state with unknown consequences to the renal function, thus the meaning of that finding is unclear. CPB has been blamed for many years as responsible for renal dysfunction in cardiac patients, however in most of the recent trials CPB has not been associated as being an independent risk factor for renal perioperative renal failure.3 Interestingly, studies with off pump surgery has shown the same incidence of renal dysfunction in patients with preoperative abnormal renal function. 4 I agree with the authors that hypothermia seems to be the best protective intervention in these patients, mainly due to metabolism reduction. Drugs that increase blood flow non-specifically, have not shown benefit so far. Reference. 1 Loef B G, Henning R H, Navis G, et al. Changes in glomerular filtration rate after cardiac surgery with cardiopulmonary bypass in patients with mild preoperative renal dysfunction. Br J Anaesth 2008; 100: 759-64 2 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 3 Brown J R, Cochran R P, Leavitt B J. et al. Multivariable prediction of renal insufficiency developing after cardiac surgery. Circulation 2007; 116:I39-I43 4 Di Mauro M, Gagliardi M, Iaco A, et al. Does off-pump coronary surgery reduce postoperative acute renal failure? The importance of preoperative renal function. Ann Thorac Surg 2007; 84: 1496-503 Dr Guillermo Lema Dr Jorge Urzúa Dr Roberto Jalil Dr Roberto Canessa Departments of Anaesthesiology and Nephrology Pontificia Universidad Católica de Chile. Santo Tomas University Santiago, Chile Grant FONDECYT 1030645-2003 Conflict of Interest:None declared |
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