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The Dartmouth Institute for Health Policy and Clinical Practice, One Medical Center Dr, Lebanon, NH 03756
(Email: jeremiah.brown{at}dartmouth.edu).
Di Mauro and colleagues [1] investigated the renoprotective effect of off-pump coronary artery bypass surgery compared with on-pump surgery using cardiopulmonary bypass. The authors stratified the analysis into two groups: (A) patients with normal baseline renal function (serum creatinine < 1.5 mg/dL) and (B) patients with abnormal baseline renal function (serum creatinine 
1.5 mg/dL). Their analysis addressed the following question: Does off-pump surgery have a renoprotective effect compared with on-pump surgery with cardiopulmonary bypass support? Propensity score matching was used to balance patients undergoing on-pump and off-pump surgery in both of the analytical strata. The outcomes of the analyses were survival and 30-day acute renal failure, defined as a postoperative serum creatinine of 2.0 (mg/dL) if the baseline creatinine was <1.5 mg/dL or a 1.0 mg/dL increase in creatinine if the baseline creatinine was 1.5 mg/dL.
Among propensity-matched patients with normal renal function prior to surgery (analysis A), patients undergoing off-pump surgery were less likely to have acute renal failure develop (2.9%) than patients undergoing surgery with cardiopulmonary bypass support (7.9%). Multivariable stepwise logistic regression analysis confirmed that cardiopulmonary bypass with more than 66 minutes of pump time was a significant independent predictor of acute renal failure as well as low ejection fraction < 35%. However, among patients with pre-existing abnormal renal function (analysis B), the occurrence of acute renal failure at 30 days was similar for off-pump (12.5%) and on-pump (16.3%) patients. Ten-year survival analysis demonstrated a similar finding showing off-pump surgery with significantly higher survival in comparison with on-pump for analysis A (p value 0.026), but not with analysis B (p value 0.230).
The authors extended their primary hypothesis to compare the survivorship of patients undergoing on-pump versus off-pump surgery but stratified by the development of postoperative acute renal failure. The authors showed that acute renal failure was a significant predictor of early mortality (30-day) and late mortality (10-year). However, on-pump and off-pump survival were not significantly different within the acute renal failure strata. Therefore, acute renal failure increased the risk of mortality regardless of the surgical strategy.
There has been a lack of consensus in the surgical community regarding the renoprotective effectiveness of off-pump surgery compared with on-pump cardiopulmonary bypass surgery. Di Mauro and colleagues [1] showed a significant survival advantage for off-pump patients with normal preoperative renal function. Di Mauro and colleagues’ [1] findings are in agreement with a recent review by Raja and Dreyfus [2], who reported that 3 of 4 randomized controlled trials demonstrated a renoprotective effect of off-pump surgery among patients with normal preoperative renal function. However, a recent meta-analysis reported a summary estimate from five randomized controlled trials showing no significant renoprotective effect for off-pump surgery with an odds ratio of 0.61 (range, 0.25 to 1.47) [3]. The meta-analysis also reported a summary estimate among eight off-pump observational studies showing a significant renoprotective effect with an odds ratio of 0.54 (range, 0.37 to 0.77) [3]. The observational meta-analysis suggests off-pump surgery has a 46% reduction in acute renal failure. The association of acute renal failure and survival has been previously reported [4], and a report by Stallwood and colleagues [5] also reported acute renal failure and not surgical procedure (on-pump or off-pump) impacted 30-day survival [5].
Unfortunately, propensity score analysis and observational studies lack the ability to adjust for surgeon preference for conducting an on-pump or off-pump case. Such preferences may include coronary anatomy, location, and access to target vessels. Despite the lack of consensus in the literature on the topic, the following observations are consistent: postoperative renal dysfunction impacts short-term and long-term survival and efforts to protect renal function perioperatively without jeopardizing complete revascularization and graft patency is paramount.
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