Ann Thorac Surg 2007;84:1426-1427
© 2007 The Society of Thoracic Surgeons
Correspondence
Minimally Invasive Closed Circuit Versus Standard Cardiopulmonary Bypass: Is It Renoprotective?
Robert H. Habib, PhDa,b,
Anoar Zacharias, MDc,d,
Thomas A. Schwann, MDc,d
a Division of Cardiovascular Surgery, St. Vincent Mercy Medical Center, 2213 Cherry St, ACC Bldg, Suite 309, Toledo, OH 43608
b Departments of Pediatrics and Medicine, University of Toledo, College of Medicine, Toledo, OH
c Division of Cardiovascular Surgery, St. Vincent Mercy Medical Center, 2213 Cherry St, ACC Bldg, Suite 309, Toledo, OH 43608
d Departments of Surgery, University of Toledo, College of Medicine, Toledo, OH 43699
(Email: robert_habib{at}mhsnr.org).
To the Editor:
We read with great interest the article by Castiglioni and colleagues [1]. Their results, albeit based on 40 randomized patients, argue in favor of the minimally invasive closed circuit (MECC) cardiopulmonary bypass system (CPB). The difference in the hematocrit profiles and transfusion rates are impressive. The adverse effects of both excessive on-pump hemodilution and red blood cell transfusion on postoperative organ function and patient outcomes have been the focus of recent research [2, 3]. We noted that Castiglioni and colleagues [1] do not report a significant difference in renal outcomes for the MECC versus the conventional CPB groups. This result, given their hemodilution and transfusion data, is counter to what is expected based on the most recent investigations on the topic [4, 5]. A plausible explanation for this finding is that this relatively small randomized trial is insufficiently powered to detect significant differences in incidence of renal dysfunction or creatinine levels (see Table 5 [1]).
Alternatively we suggest that the renoprotective effects of reducing hemodilution and packed red blood cell transfusions achieved by using MECC bypass or similar CPBs were not optimally investigated in this case. To explain this we note the following: First, the difference in the preoperative creatinine levels for the conventional group (0.73 ± 0.11 mg/dL) versus the MECC group (1.60 ± 2.09 mg/dL) was substantial even if it did not reach statistical significance. Second, postoperative peak creatinine values for the conventional group (1.08 ± 0.90 mg/dL) indicated an average 48% increase relative to preoperative levels, whereas the corresponding MECC data (1.38 ± 1.17 mg/dL) indicated an average 14% decrease. Third, these diverging renal effects may have been artificially narrowed due to the less hemodiluted state in MECC patients (ie, higher postoperative hematocrits; see Figure 2 [1]), which has the relative effect of concentrating the creatinine in the blood. Thus, we contend that the authors’ conclusion on renal effects are likely to differ had they considered the absolute creatinine change (
Cr) or the percent change in creatinine (%Cr), or both, relative to preoperative values of individual patients [5]. Indeed, the group-averaged creatinine data suggest that the Cr and %Cr will probably be significant for the two groups, and the magnitude of these differences may confer an important clinical effect when extrapolated to the entire cardiac surgery population.
In conclusion, we believe that the potential benefits of reducing hemodilution and transfusion achieved by MECC CPB or other miniaturized CPBs could be realized, especially pertaining to renal morbidity. Moreover, we believe that Castiglioni and coworkers [1] may have the initial prospective randomized data to show this, and we believe that a re-evaluation of the creatinine data as previously suggested is worthwhile. We look forward to seeing this work done and reported, perhaps in response to this commentary.
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References
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- Castiglioni A, Verzini A, Pappalardo F, et al. Minimally invasive closed circuit versus standard extracorporeal circulation for aortic valve replacement Ann Thorac Surg 2007;83:586-591.[Abstract/Free Full Text]
- Habib RH, Zacharias A, Schwann TA, Riordan CJ, Durham SJ, Shah A. Adverse effects of low hematocrit during adult cardiopulmonary bypass: should current practice be changed? J Thorac Cardiovasc Surg 2003;125:1438-1450.[Abstract/Free Full Text]
- Koch CG, Li L, Duncan AI, et al. Morbidity and mortality risk associated with red blood cell and blood-component transfusion in isolated coronary artery bypass grafting Crit Care Med 2006;34:1608-1616.[Medline]
- Karkouti K, Beattie WS, Wijeysundera DN, et al. Hemodilution during cardiopulmonary bypass is an independent risk factor for acute renal failure in adult cardiac surgery J Thorac Cardiovasc Surg 2005;129:391-400.[Abstract/Free Full Text]
- Habib RH, Zacharias A, Schwann TA, et al. Role of hemodilutional anemia and transfusion during cardiopulmonary bypass on renal injury after coronary revascularization: implications on operative outcome Crit Care Med 2005;33:1749-1756.[Medline]
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