Remote Ischemic Preconditioning During Cardiopulmonary Bypass

Lactic Acidosis

Ischemic preconditioning, Lactate level, Cardiopulmonary bypass

The objective of study is to detect effect of remote ischemic preconditioning on serum lactate levels during and after cardiac surgery with cardiopulmonary bypass in addition to its effect on cardiac and renal clinical outcomes.

Remote ischemic preconditioning (RIPC) is a phenomenon where transient non-injurious ischemia/ reperfusion episodes applied to an organ away from the heart can protect the myocardium from ischemia/reperfusion injury. RIPC has been found to be an attractive strategy to reduce myocardial injury and improve outcome in patients undergoing cardiac surgery. The exact mechanisms of this protection are not yet known, although stimulation of prosurvival intracellular kinase responses and inhibition of inflammatory pathways each play a role. RIPC can be performed by noninvasive inflation and deflation of a standard blood pressure cuff or pneumatic tourniquet on the upper or lower limbs to induce brief ischemia and reperfusion, which is the mechanism by which injury in patients undergoing open cardiac surgery occurs. ANESTHETIC TECHNIQUE All patients will be preoperatively examined and investigated by complete blood count, coagulation profile, renal and kidney functions and electrolytes. Electrocardiography, chest x ray and echocardiography will be routinely done. Coronary angiography and carotid arterial duplex will be requested in patients prepared for coronary artery bypass graft (CABG). Patient will be premedicated by intramuscular injection of 10mg morphine in the morning of the operation. Before induction of anesthesia, a five-lead electrocardiography system will be applied to monitor heart rate, rhythm, and ST segments (leads II and V5). A pulse oximeter probe will be attached, and a peripheral venous cannula will be placed. For measurement of arterial pressure and blood sampling, a 20 G cannula will be inserted into either right or left radial artery under local anesthesia. General anesthesia will be induced by fentanyl (3-5 μg/kg), propofol titrated according to response, followed by atracurium (0.5 mg/kg). Trachea will be intubated, patients will be mechanically ventilated with oxygen in air so as to achieve normocarbia. This will be confirmed by radial arterial blood gas analysis. An esophageal temperature probe and a Foley catheter will also be placed. For drug infusion, a triple-lumen central venous catheter will be inserted via the right internal jugular vein. Anesthesia will be maintained by inhaled isoflurane, with additional fentanyl injected prior to skin incision as well as sternotomy and atracurium infusion for continued muscle relaxation. During extracorporeal circulation, patients will receive propofol infusion in addition to atracurium infusion. Before initiation of cardiopulmonary bypass (CPB), the patients will receive intravenously tranexamic acid (2 g) and heparin (300-500 units/kg body weight) to achieve an activated clotting time \> 400 s. CPB was instituted via an ascending aortic cannula and a two-stage right atrial cannula. Before, during, and after CPB (pump blood flow: 2.4 l/min/m2), mean arterial pressure was adjusted to exceed 60 mmHg. Cardiac arrest will be induced with cold antegrade crystalloid cardioplegia (St Thomas solution) or warm intermittent antegrade blood cardioplegia. Lactate-enriched Ringer's solution will be added to the CPB circuit to maintain reservoir volume when needed, and packed red blood cells will be added when hemoglobin concentration decrease to less than 7 g/dl. After rewarming the patient to 37°C and separation from CPB, reversal of heparin by protamine sulfate, and sternal closure, the patients will be transferred to the intensive care unit.

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