Influence of Preoperative Hemodialysis or Intraoperative Modified Ultrafiltration on Postoperative Outcome for Patients With Severe Renal Dysfunction Undergoing Open Heart Surgery: Randomized, Controlled, Multicenter Clinical Trial

1. BACKGROUND

1.1. RENAL DYSFUNCTION AND OPEN HEART SURGERY:

The incidences of both cardiovascular disease (CVD) and chronic renal dysfunction (RD) are increasing with the aging population in the western world (1). The intense relationship between the pathogenesis of CVD and chronic RD has recently been reviewed by Schiffrin et al, in detail (2). They both have common risk factors such as diabetes, hypertension, activation of renin-angiotensin system, endothelial dysfunction, oxydative stress, etc. Besides, each has an impact on the other's outcome. On the one hand, CVD is the most frequent cause of death in chronic RD patients (3). On the other hand, even mild chronic RD is one of the major risk factors of postoperative mortality and morbidity after cardiac operations (4, 5). The mechanism is not clear yet, however, volume overload, electrolyte imbalance and inflammatory state created by cardiopulmonary bypass (CPB) may have an impact. Zakeri et al showed that in-hospital mortality after isolated primary coronary artery bypass grafting (CABG) increases exponentially with increasing levels of renal dysfunction (6). They reported an in-hospital mortality of 2.2%, 4.3%, 9.3% and 14.8% in patients who have a preoperative serum creatinine level (SCr) of <130 µmol/L, 130-149 µmol/L, 150-179 µmol/L and 180-199 µmol/L, respectively. These results were similar to the study published previously by Weerasinghe et al with the same cut-off levels of SCr (7). Using the Glomerular Filtration Rate (GFR) instead of SCr, Cooper et al. came to the same conclusion after analysing 483,914 patients receiving isolated CABG in the Society of Thoracic Surgeons (STS) National Adult Cardiac Database (5). They reported that operative mortality rose inversely with declining renal function, from 1.3% for those with normal renal function to 1.8%, 4.3% and 9.3% for patients with mild, moderate and severe RD, respectively. Another study regarding the effect of preoperative RD on mortality after valve surgery was also published with a relatively smaller patient population (8). Although the RD group had significantly worse outcomes with regard to postoperative ventilation time, re-operation, blood transfusion and length of hospital stay, operative mortality was not statistically different between the two groups (3.4% for RD group vs. 2.3% for the control group), probably because of small sample size. However, Filsoufi et al. reported an increased mortality for patients having SCr of >2.5 mg/dL after single valve replacement (25.0% vs. 2.4%),multiple valve replacement (26.7% vs. 3.4%), and combined valve replacement with CABG (28.0% vs. 4.6%) in a large, single-center cohort (9). Regarding long-term survival, Devbhandari reported 1-, 3- and 5-year survival rates following on-pump coronary bypass surgery as 90.3%, 83.2% and 71.4% for non-dialysis dependent renal dysfunction (NDDRD) patients, and 97.4%, 94.6% and 91.0% for patients with no history of RD, respectively (10). Chronic RD affects not only the operative mortality, but also the morbidity after open heart surgery. It has been shown that preoperative RD is an independent predictor of postoperative acute RD and hemodialysis (HD) (5, 7, 9-12) as well as gastrointestinal (GI) (4, 9), respiratory (5, 9), infectious (5) and neurological (5) complications.

1.2. HEMODIALYSIS:

HD is the most common renal replacement therapy for decades, for those who have end-stage RD and have not received renal transplantation. Intermittent HD is a very efficient method to decrease blood urea and creatinine as well as to treat volume overload. Intermittent HD can be performed temporarily in the setting of acute RD or permanently in the setting of chronic RD. In chronic RD, 3 sessions of 4 hours are usually prescribed to adequately substitute the renal function. A good vascular access is essential to perform HD. A temporary dual- or tri-lumen dialysis catheter has to be inserted into a central vein such as the internal jugular, the subclavian or the femoral vein.