Saudi Journal of Kidney Diseases and Transplantation

: 2010  |  Volume : 21  |  Issue : 6  |  Page : 1081--1087

Impact of mild renal impairment on early postoperative mortality after open cardiac surgery

A Abdel Ghani1, Muath Al Nasar2, E Al Shawaf3, I Vislocky3,  
1 Department of Nephrology, Mubarak Al Kabeer Hospital, Kuwait
2 Department of Internal Medicine, Mubarak Al Kabeer Hospital,Ministry of Health, Kuwait
3 Department of Anesthesia, Critical Care-Chest Disease Hospital, Kuwait

Correspondence Address:
A Abdel Ghani
Nephrology Department, Mubarak Al Kabeer Hospital, P.O. Box 43787


Preoperative severe renal impairment is included in the risk scores to predict out­come after open cardiac surgery. The purpose of this study was to assess the impact of pre­operative mild renal impairment on the early postoperative mortality after open heart surgery. Data of all cases of open cardiac surgery performed from January 2005 to June 2006 were collec­ted. Cases with preoperative creatinine clearance below 60 mL/min were excluded from the study. Data were retrospectively analyzed to find the impact of renal impairment on short-term outcome. Of the 500 cases studied, 47 had preoperative creatinine clearance between 89-60 mL/min. The overall mortality in the study cases was 6.8%. The mortality was 28.7% in those who developed postoperative ARF, 33.3% in those who required dialysis and 40.8% in those with preoperative mild renal impairment. Binary logistic regression analysis showed that female gender (P = 0.01), preoperative mild renal impairment (P = 0.007) as well as occurrence of multi organ failure (P < 0.001) were the only independent variables determining the early postoperative mortality after cardiac surgeries. Among them, preoperative mild renal impairment was the most significant and the best predictor for early postoperative mortality after cardiac surgery. Our study suggests that renal impairment remains a strong predictor of early mortality even after adjustment for several confounders.

How to cite this article:
Ghani A A, Al Nasar M, Al Shawaf E, Vislocky I. Impact of mild renal impairment on early postoperative mortality after open cardiac surgery.Saudi J Kidney Dis Transpl 2010;21:1081-1087

How to cite this URL:
Ghani A A, Al Nasar M, Al Shawaf E, Vislocky I. Impact of mild renal impairment on early postoperative mortality after open cardiac surgery. Saudi J Kidney Dis Transpl [serial online] 2010 [cited 2021 Oct 23 ];21:1081-1087
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Full Text


Cardiovascular disease remains the number one cause of mortality in general population. Renal Impairment (RI), ranging from new onset of mild reversible impairment to irreversible end-stage renal disease (ESRD) requiring renal replacement therapy, has been found to be a significant non-traditional risk factor for car­diovascular death and all cause mortality. [1],[2] Both renal insufficiency and ESRD are impor­tant risk factors for patients undergoing car­diac surgery. [3] The identification of preopera­tive risk factors for adverse outcome after cardiac surgery is an important component of preoperative care. It identifies high-risk-patients requiring special care and in whom, new inter­ventions can be developed to improve out­come. [4] Several studies have assessed the risk associated with mild or moderate RI in pa­tients undergoing coronary artery bypass sur­gery (CABG). [5],[6],[7] In these studies, renal func­tion has been defined based on levels of serum creatinine and not according to calculated creatinine clearance (Cr Cl).

Plasma creatinine level is a highly specific marker of RI. However, it may be insensitive to mild and moderate degrees of RI because it depends on many non-renal factors including muscle mass, gender and metabolism. [8],[9] Recent data demonstrated that estimated Cr Cl is a very powerful predictor of outcome in patients with acute myocardial infarction and is more accurate in this respect than serum creatinine. [10],[11]

The aim of the present study was to assess the impact of mild RI (preoperative estimated Cr Cl 89-60 mL/min) on the short-term out­come (30 days) after open heart surgeries.

 Subjects and Methods

A retrospective single center study was con­ducted in the Kuwait chest disease hospital from January 2005 to June 2006. Data from all cases who underwent open cardiac surgery was collected including: age, weight, height, gender, presence of congestive heart failure defined as ejection fraction below 35%, pre­sence of diabetes mellitus (random plasma sugar level more than 7 mmol/dL and/or his­tory of use of hypoglycemic agents), preope­rative estimated Cr Cl using Cockcroft and Gault equation, [12] hypertension, chronic obs­tructive airway disease, and recent myocardial infarction (within one month of surgery). Ope­rative data including type of surgery, extra­corporeal circulation time (ECCT), cross clamp time (C-clamp) and postoperative data inclu­ding the need of vasopressors, prolonged me­chanical ventilation > 48 hours, presence of multi organ failure (MOF) defined as more than two organ/system failure, postoperative hemorrhage and/or infection, development of postoperative acute renal failure (ARF) defined as more than 25% increase of serum creatinine from preoperative levels, the need for dialysis and the early postoperative mortality within the first 30 days post surgery were also collected. Preoperative mild RI was defined as Cr Cl 89­60 mL/min. Patients with Cr Cl less than 60 mL/min, those with ESRD requiring dialysis, those on mechanical ventilator before surgery and patients with missing data were excluded from the study.

 Statistical Methods

Data were analyzed using SPSS for windows version 13 (SPSS, Inc, Chicago, IL). Numerical variables were expressed as mean ± SD, whereas categorical variables were expressed as frequencies and percentages. Fisher exact test was used for univariate analysis using risk ratio and 95% confidence interval (CI). Logistic regression analysis was used for multivariate analysis of statistically significant variables in the univariate analysis. Results were consi­dered statistically significant if the P value was < 0.05.


A total of 885 cases underwent open heart surgery from January 2005 to June 2006 of whom, 385 cases had one or more exclusion criteria and were excluded from the study. Five hundred cases with preoperative Cr Cl above 60 mL/sec were enrolled in the study which included 369 males (73.8%) and 131 females (26.2%). The patients' clinical charac­teristics are described in [Table 1]. The overall mortality in the study cases was 6.8%. The mortality was 28.7% in those who developed postoperative ARF, 33.3% in those who re­quired dialysis and 40.8% in those with preoperative mild renal impairment [Figure 1]. Univariate analysis showed that female gender (P = 0.02), hypertension (P = 0.02), COAD (P = 0.01), preoperative renal impairment (P < 0.001), EF below 35% (P < 0.001), ECCT > 100 minutes (P = < 0.001), C-clamp time > 60 minutes (P = 0.004), post operative hemo­rrhage (P < 0.001), postoperative infection (P < 0.001), use of more than two vasopressors (P < 0.001), postoperative ARF (P < 0.001), pro­longed mechanical ventilation (P < 0.001) and the presence of MOF (P < 0.001) as factors contributing to early postoperative mortality [Table 2]. Binary logistic regression analysis showed that female gender (P = 0.01), pre­operative mild RI (P = 0.007), as well as MOF (P < 0.001) were the only independent varia­bles determining the early postoperative mortality after cardiac surgeries; among them, mild RI was the most significant and the best pre­dictor [Table 3].{Table 1}{Table 2}{Table 3}{Figure 1}


It has been previously established that pa­tients with severe RI such as those requiring dialysis, have poor short-term outcome follo­wing CABG. [13],[14] The two most common risk stratification scoring systems used to estimate perioperative mortality, give a weighting fac­tor only for advanced renal disease or dialysis dependency. [1],[2] The present study established a strong link between preoperative mild RI and postoperative short-term mortality. Multivariate analysis showed that the preoperative Cr Cl is the most important predictor of early post­operative mortality followed by female gender and the presence of postoperative multi organ failure. This is in accordance with previous studies. [5],[15],[16],[17],[18],[19],[20] Hayashida et al reported that RI was the second most important predictor of operative mortality after poor left ventricular failure. [21] Also, Mageed et al [15] reported RI as the second most important predictor of early postoperative mortality after timing of surgery.

The mechanism by which RI contributes to perioperative mortality is unknown, but pa­tients with mild RI had a high prevalence of traditional cardiovascular risk factors including increased levels of inflammatory mediators, [22] hypercoagulability, [22] endothelial dysfunction, [23] arterial stiffness, [24] calcification [25] and left ven­tricular hypertrophy. [26] Moreover, patients with RI have an increased risk of developing ARF, bleeding, strokes and needing prolonged ven­tilation. [27] They are often considered to be im­munocompromised, [28] which may render them less able to recover quickly and has been asso­ciated with greater mortality after cardiac sur­gery. [29]

Most previous studies assessed the associa­tion between renal function and outcome after cardiac surgery by using the plasma creatinine level, but estimated Cr Cl seems to be a better predictor in these patients. [17],[30] Wang et al [30] confirmed that even if lower values of plasma creatinine were used to define renal dysfunc­tion, estimated Cr Cl would remain a better risk predictor in these patients.

Detection of preoperative renal function is important as the presence of RI makes the kidney more vulnerable to ischemia and drug induced toxicity. [15],[31],[32],[33],[34] Thus, estimated pre­-operative Cr Cl could influence perioperative care by trying to improve renal function before surgery and minimizing the exposure to poten­tially nephrotoxic agents before, during and after surgery. Although the impact of these interventions on outcome is unknown, the in­creased morbidity or mortality associated with postoperative deterioration of renal function probably justifies any attempt to minimize perioperative renal insults in patients with pre­existing renal impairment. [32]

Preoperative mild RI is a strong predictor of early postoperative mortality in patients under­going cardiac surgeries. We suggest that all patients scheduled to undergo CABG should have their renal function carefully assessed by using estimated Cr Cl instead of plasma crea­tinine concentration to better determine the risk of early postoperative death at no extra cost or inconvenience to the patient.

 Limitations of the Study

First, the study was conducted at a single center and the results might not be applicable to all other centers performing thoracic sur­geries. Second, although the Cockcroft and Gault equation provides an acceptable estimate of Cr Cl in most stable cardiac patients, it may underestimate the GFR, which in turn over­estimates the risk in obese patients and in pa­tients with very low plasma creatinine levels. [35] Additionally, the formula may overestimate

creatinine clearance in hemodynamically un­stable patients with acute renal failure since plasma creatinine levels may not have time to reach its peak and in turn, may underestimate risk prediction.


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