|Year : 2017 | Volume
| Issue : 4 | Page : 113-114
Renal dysfunction after off-pump coronary artery bypass grafting surgery: Are the current guidelines too relaxed and deliberately extrapolated?
Sandeep Kumar Kar
Department of Cardiac Anaesthesiology, Institute of Postgraduate Medical Education and Research, Kolkata, West Bengal, India
|Date of Web Publication||29-Dec-2017|
Dr. Sandeep Kumar Kar
Assistant Professor, Department of Cardiac Anaesthesiology, Institute of Postgraduate Medical Education and Research, Kolkata, West Bengal
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Kar SK. Renal dysfunction after off-pump coronary artery bypass grafting surgery: Are the current guidelines too relaxed and deliberately extrapolated?. J Integr Nephrol Androl 2017;4:113-4
|How to cite this URL:|
Kar SK. Renal dysfunction after off-pump coronary artery bypass grafting surgery: Are the current guidelines too relaxed and deliberately extrapolated?. J Integr Nephrol Androl [serial online] 2017 [cited 2018 Jan 17];4:113-4. Available from: http://www.journal-ina.com/text.asp?2017/4/4/113/222067
In developing countries, the focus has shifted more toward conducting Off-pump coronary artery bypass grafting (OPCABG), the reasons might help me the lower cost involved and a shorter hospital stay. There are no concrete guidelines regarding optimization of preoperative hypertension in patients undergoing OPCABG. It has often observed and has been mentioned in Kaplan Textbook of cardiac anesthesia 6th edition Echo Era that patient with systolic blood pressure (BP) >180 undergoing coronary artery bypass grafting (CABG) should not be cancelled on the day of surgery; however, the authors have advocated that the pressure to be maintained intraoperatively should not be <20% of the preoperative systolic pressure, to maintain normal glomerular blood flow. This may be true in case of CABG conducted under cardioplegic arrest, but the developing world seems to extrapolate this practice which seems to be valid for on-pump CABG deliberately extrapolated to OPCABG resulting in an increased prevalence of renal dysfunction and postoperative delirium in the postoperative period. Many cardiac surgery risk scoring systems have not given adequate impetus to preexisting hypertension and diabetic autonomic neuropathy leading to inadequate and improper preoperative optimization of the patients undergoing OPCABG.
Risk factors for acute kidney injury (AKI) are common among patients undergoing cardiac surgery, and dubiously explain in the absence of concrete guidelines segregating the preoperative optimization strategies of hypertension management in patient undergoing CABG surgery under cardioplegic arrest or OPCABG attributing AKI occurrence in up to 30% of patients undergoing coronary artery surgery.
The peculiar hemodynamic conditions in OPCABG surgery, including cardiopulmonary bypass (CPB), aorta cross-clamping, high rates and volumes of exogenous blood product transfusion, and high doses of exogenous vasopressors (used both in the intraoperative period and the postoperative period as well), increase the risk of AKI. These factors alter renal perfusion, forcing the kidney to work sometimes outside the range of its auto-regulatory pressure limits inducing cycles of ischemia and reperfusion, increase oxidative damage, and increase renal and systemic inflammation, implicated in the development of AKI. The quantification of renal dysfunction adopted in the formulation of studies and trials investigating renal dysfunction after CABG have been poorly planned with some studies taking creatinine >2 mg/dL, whereas others have defined renal dysfunction in terms of postoperative requirement of dialysis.
Renal perfusion is complex and highly regulated. Although 20% of cardiac output perfuses the kidneys, the majority of blood filtered by cortex glomeruli is shunted away from the vasa recta. This shunt may help in maintaining the electrolyte and water concentration gradients in the renal medulla required for tubule and collecting system reabsorption, but renders the renal medulla and corticomedullary junction hypoxic relative to other tissues (PO2 10–20 mmHg). This could be a protective mechanism for oxidative injury but magnifies ischemic insult. During OPCABG surgery, the BP is maintained at 85–90 mm of Hg (systolic BP) to facilitate grafting in the coronary arteries even in patients suffering from hypertension with altered renal autoregulation, which is set at a higher level leading to the alteration of renal perfusion, and increasing the vulnerability of the tubules at the corticomedullary junction and in the medulla to ischemia.
Preoperative prediction of AKI provides the opportunity for clinicians to optimize high-risk patients, intensive monitoring, and initiate preventative and therapeutic treatments. Several risk stratification systems exist for cardiac surgery patients. The best-validated scores predict severe AKI requiring dialysis and include the Cleveland Clinic Score and the Mehta Score., These scores use similar risk factors to predict AKI, although the Cleveland Clinic score offers the best discrimination. However, the intraoperative conditions in patients undergoing coronary artery surgery under cardioplegic arrest and patients undergoing OPCABG are markedly different. The author believes that any ischemia occurring in CABG done under cardioplegic arrest under CPB as an accident or mishap; however, any ischemia in OPCABG is deliberate as grafting is done in hypotensive conditions even in patients with untreated hypertension (with upper-level shifting of the renal perfusion pressure threshold of autoregulatory mechanism). OPCABG is more challenging with increased episodes of ischemia in patients with diabetes undergoing OPCABG, manifesting in an increased incidence of postoperative renal dysfunction. Therefore, separate preoperative hypertension guidelines for peri-operative optimization of patients undergoing CABG either on the pump or by OPCABG need to be formulated by competent societies after refining the criteria of renal dysfunction quantification uniformly by conduction appropriately designed trials. This would in turn pay due respect to renal autoregulation and autoregulatory alterations occurring in hypertensive patients, adequate treatment and optimization of hypertension spanning over 6–8 weeks with angiotensin-converting-enzyme inhibitors and beta-blockers, allowing gradual down setting of the renal autoregulatory threshold.
Efforts need to be directed to reduce AKI following cardiac surgery and its influence on postoperative patient morbidity due to hemodynamic manipulations (especially during OPCABG), appropriate intravenous resuscitation strategies including goal-directed therapy and the identification and mitigation of modifiable risk factors and giving adequate respect to renal autoregulatory mechanisms, giving adequate time to the Nephrologist to optimize anti-hypertensive therapy to down set it to acceptable preoperative levels that would minimize post- and intra-operative renal ischemic insult. However, when optimized patients were taken in a study conducted in India conducted on OPCABG has been associated with risk reduction of postoperative AKI compared with on-pump CABG with CPB. Hence, the emphasis is to be given on perioperative optimization of fisk factors that contribute to renal dysfunction after cardiac surgery.
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