Impact of preoperative mild renal dysfunction on short term outcome in isolated Coronary Artery Bypass (CABG) patients.

BACKGROUND AND AIM: It is well known that dialysis dependent renal failure increases the likelihood of poor outcome following cardiac surgery. But the results of CABG in patients with mild renal dysfunction are not clearly established. The aim of the study is to analyze the risk of preoperative mild renal dysfunction on outcome after isolated coronary surgery.
MATERIALS AND METHODS: We reviewed prospectively collected data between June 2006-Nov 2006 in 488 patients who underwent isolated CABG. We separated the data into two groups. Control group having normal renal function and study group having mild renal dysfunction (serum creatinine 1.4 mg-2.2 mg%). Among 488 patients, 412 patients were in control group and 76 patients were in the study group.
RESULTS: Analysis of data showed significant postoperative complications in the mild renal dysfunction group, like increased operative mortality (7.5% vs 1.6%), increased requirement of postoperative renal replacement therapy (10% vs 1.2%), increased incidence of new onset atrial fibrillation (20% vs 4.2%) and prolonged duration of ICU stay. Multivariate analysis adjusting for known risk factors confirmed preoperative mild renal dysfunction (S.creat.1.4-2.2 mg/dl) is an independent risk factor for postoperative morbidity and mortality. (Adj. OR: 4.47; 95% CI: 1.41-14.16; P=0.010).
CONCLUSION: Mild renal dysfunction is an important independent predictor of outcome in terms of in-hospital mortality and morbidity in patients undergoing CABG.

Introduction

Renal failure predisposes patients to adverse outcome after coronary artery bypass surgery. Moderate to end stage renal dysfunction is known to be an important predictor of morbidity and mortality after CABG and in this group a 5-year survival of less than 50% has been observed.[1] The two most common risk stratification scoring systems used to estimate perioperative mortality give a weighting factor only for advanced renal disease i.e. S.creatinine >200 umol/l or dialysis dependency.[23]

It is now recognized that even minor renal dysfunction as reflected by an increase in serum creatinine (or, more precise, by estimated GFR) on one hand and/or albuminuria or trace proteinuria on the other hand, has a major impact on cardiovascular risk.[4] Although a higher cardiovascular risk in patients with proteinuria had been recognized two decades ago,[5] both the consistency and the magnitude of cardiovascular risk which is associated with minor renal dysfunction have been fully appreciated only in the recent past.[67] Recently it is emphasized that increased risk of cardiovascular adverse events does exist even in patients with mild renal dysfunction and the magnitude of this risk is so large that there are recent efforts to give renal dysfunction the status of a major cardiac risk factor, similar to diabetes mellitus.[89] Several studies have shown that patients with mild renal dysfunction have an increased risk of mortality within 30 days of coronary surgery.[1011]

There are several mechanisms[4] postulated through which impaired renal function causes cardiovascular morbidity such as:

Early activation of sympathetic nervous system as a result of excitation of intrarenal chemoreceptors and mechanoreceptors that send activating signals into the hypothalamus where catecholamine turnover is increased leading to increased efferent sympathetic nerve traffic[1213] (this may occur even when GFR is still normal).

increased atherogenesis leading to oxidative stress[14]

Early increase of blood pressure and left ventricular remodeling with evidence of impaired left ventricular diastolic function, insulin resistance, and a state of micro inflammation.

Increased concentration of an inhibitor nitric oxide synthetase-ADMA (asymmetric dimethyl-L- arginine).[15]

In the background of this information, it is imperative that special attention be focused on the outcome of CABG in patients with mild renal dysfunction. Few studies have been conducted in this context recently and have found significant risk of perioperative mortality among patients with mild renal dysfunction following CABG.[1617] Results from these studies suggested that preoperative mild renal dysfunction is an independent predictor of mortality and morbidity in patients who undergo CABG.

Our study aims at investigating the impact of mild renal dysfunction (s.creatinine=1.4-2.2 mg/dl) in patients who have been undergoing elective isolated CABG in our hospital so that it provides some additional information regarding preoperative risk stratification.

Materials and Methods

The study was conducted in patients undergoing isolated first time CABG at Narayana Hrudayalaya Institute of Medical Sciences. The data was collected prospectively as a part of preoperative risk stratification of patients undergoing CABG. Data were collected for a duration of six months between June 2006 to Nov 2006 and a total number of 488 patients were enrolled.

We analyzed data in all the patients undergoing first time isolated CABG with no history of renal disease or dialysis and with a preoperative serum creatinine >1.4 and < 2.2 mg/dl.

The patients were stratified into two groups:

Mild renal dysfunction group (S.creatinine 1.4-2.2mg/dl: N=76 )

Control group with normal renal function (S.creatinine < 1.4mg/dl: N=412)

The patients' glomerular filtration rate (GFR) was estimated using the Cockroft-Gault formula = (140 – age) × weight(kg)/(serum creatinine × 72 [×0.85 for women] and adjusted for each 1.73 m2 of body surface area. Renal dysfunction was defined as GFR< 60 mL/min per 1.73 m2 in accordance with the U.S. National Kidney Foundation guidelines.

Statistical Analysis

Continuous data with normal distribution are given as mean ± standard deviation, otherwise as median, student t test for testing the significance of mean, Chisquare or Fisher exact test for testing the significance of percentages. OR –odds ratio and its 95% Confidence Interval have been used to find the relationship of outcome between two groups of patients. Multivariate analysis by logistic regression done for postoperative complications adjusting to various preoperative risk factors

If OR=1, outcome equally likely b/w two groups.

If OR>1, outcome is more likely in mild Renal dysfunction group

If OR< 1, outcome is less likely in mild Renal dysfunction group.

+ Suggestive significance 0.05

* Moderately significant 0.01