Bài giảng dành cho sinh viên y khoa, bác sĩ đa khoa, sau đại học. ĐH Y Dược TP Hồ Chí Minh. 1.Introduction 2.Components of CPB 3.Anticoagulation for CPB 4.Myocardial protection 5.Effects of CPB in pediatric
CARDIOPULMONARY BYPASS 1.Introduction 2.Components of CPB 3.Anticoagulation for CPB 4.Myocardial protection 5.Effects of CPB in pediatric INTRODUCTION CPB: Techniques that temporarily substitute for the functions of the heart and lungs during surgical interventions on the cardiovascular or pulmonary system CPB → a clear field for cardiac manipulation and maintenance of pulmonary and hemodynamic stability The objective of the heart-lung pump: provide enough flow to maintain a sufficient cardiac index for tissue perfusion INTRODUCTION CPB: Patient’s systemic blood → a device where O2 is supplied to the blood & CO2 is removed → arterialized blood is pumped into the aorta Complexities of CPB: Blood does not naturally • Circulate through nonendothelially lined channels • Contain gaseous & particulate emboli • Experience nonphysiologic shear stress HISTORICAL LANDMARKS Gibbon first described and used a mechanical extracorporeal oxygenator, which he termed the heartlung machine On May 6, 1953, Gibbon performed the first successful open heart surgery in the world using a heart-lung machine while repairing an ASD In 1954, Lillehei first reported the effective use of extracorporeal circulation in repair of CHD using cross circulation with the patient's parent functioning as the oxygenator Subsequent attempts to use the heart-lung machine to help correct CHD were met with high morbidity and mortality rates until Barratt-Boyes (1971) and Castaneda (1974) attempted correction using hypothermic circulatory arrest COMPONENTS OF CPB Basic components of a CPB circuit are: A pump : generally a roller pump An oxygenator: To provide for gas exchange A reservoir: To temporarily store blood collected from the operative field & from the venous cannulas A system of tubing & cannulas: To carry blood between the patient & the pump oxygenator COMPONENTS OF CPB Cannulation The arterial cannula: – The ascending aorta (+++) – Femoral or external iliac artery, axilary artery: reoperations, aortic arch procedures, severe ascending aortic diseases The venous cannula: – Right atrium ( two stage cannula): CABG, aorta, aortic valve operation only – SVC + ICV (bicaval cannula): Operations involving the right heart chambers – Femoral veins: Difficult reoperations, substernal aortic aneurysm COMPONENTS OF CPB Venous blood is drained from the heart via a cannula in the right atrium or bicaval cannulation in the SVC, IVC Blood drains by gravity to a venous reservoir, and mixes with blood drained from the operative field by cardiotomy suction catheters After passing through a heat exchanger, the blood is passed through an oxygenator (– where oxygen and carbon dioxide are titrated- )through a rooler pump , micropore filter , and back to the body via an aortic cannula ANTICOAGULATION FOR CPB Heparin Heparin is given to prevent thrombosis from occuring in the cannula, tubing, or the pump oxygenator Heparin is chosen because it is a fast-acting anticoagulant and its action can be inhibited rapidly by protamine Heparin activates antithrombin III, which inhibits thrombin activity Heparin can be stored in the vascular endothelium and smooth muscle, contributing to heparin rebound, which is observed after discontinuation of CPB and heparin reversal Clearance of heparin also is determined by hepatic and renal function ANTICOAGULATION FOR CPB Heparin Before CPB is established, the Pt is anticoagulated by heparin IV 300-400 U /kg After ensuring that the patient is heparinized ( ACT > 400 s), the arterial & venous cannula are inserted, cleared of air, & connected to the correesponding tubing of the pump oxygenator Satisfactory anticoagulation during CPB: ACT :480s Heparin concentrations in plasma:3.5- 4.0 U/ml ANTICOAGULATION FOR CPB Protamine Protamine neutralizes heparin ( by binding to heparin and releasing antithrombin III.) & normalizes the ACT The dose of protamine required for reversal of heparin may be calculated by Measurement of the circulating heparin Administering a dose based on the total dose of heparin that was administered during the procedure, followed by confirmation that the ACT has returned to baseline ( # 0.75 to mg of protamine/ 100 U of heparin ) EFFECTS OF CPB Other Mediators of Imflammation – ↑ TNF (activated monocytes & macrophages) ↑ Endothelial cell permeability Open interendothelial cell spaces ↑ interstitial edema – Endotoxin Splanchnic ischemia & ± impaired function of Kuffer cells → translocation of bacteria from the gut → endotoxin release → stimulant of complement , endothelial cells activation , potent agonist of release of TNF EFFECTS OF CPB Protein Denaturation – Blood - gas interface → protein are denatured – Denaturation of immunoglobulins → degradation of products → activate complement cascade EFFECTS OF CPB Glucose metabolism Hyperglycemia usually accompanies the stress response associated with CPB A more common complication of paediatric CPB is hypoglycemia.( the decreased glycogen stores & reduced hepatic potential for gluconeogenesis) In patients with CHD, hepatic perfusion may be impaired further → compromised liver function Neurologic consequences of hypoglycemia are aggravated by hypothermia and other factors that may modify cerebral perfusion Glucose monitoring during CPB and rapid correction with dextrose is essential for decreasing morbidity resulting from paediatric heart surgery EFFECTS OF CPB Stress response Low perfusion, nonpulsatile flow,hypothermia, hemodilution and exposure of the blood to the tubing and surface of the pump, light anesthesia depth → release of hormones and other substances, including catecholamines, cortisol, growth hormone, prostaglandins, complement, glucose, insulin, and endorphins Other factors involved in secreting these substances include the type of anesthetic used and decreased renal and hepatic function , myocardial injury, and exclusion of the pulmonary circulation from bypass The lung normally is responsible for metabolizing and clearing many of these hormones, particularly catecholamines EFFECTS OF CPB Stress response These substances undesirable effects : → myocardial damage (catecholamines), systemic and pulmonary hypertension (catecholamines, prostaglandins), pulmonary endothelial damage (complement, prostaglandins), and pulmonary vascular reactivity (thromboxane) Additional evidence: the newborn stress response, especially the endogenous release of catecholamines, may be an adaptive metabolic response necessary for survival at birth The complete elimination of an adaptive stress response may not be desirable To what extent acutely ill neonates with CHD are dependent on the stress response for maintaining hemodynamic stability is currently unknown EFFECTS OF CPB Central nervous system effects During CPB ,air bubbles, particulate matter from the pump oxygenator, platelet aggregates & fragments, fibrin aggregates, denatured protein particles atheroma, chylomicrons may be contained in the arterial blood & distributed throughout the Pt’s arterial system Some correlation between depressed neuropsychometric test scores postoperatively & number of microemboli This problem probably contributes to neuropsychiatric abnormalities after CPB, to cardiac, pulmonary & other subsystem dysfunction EFFECTS OF CPB Central nervous system effects Neurologic injury after routine CPB is uncommon in neonates, but the risk is increased when deep hypothermic circulatory arrest (DHCA) is required Although permanent injury is less common, evidence of some neurologic injury is observed in as many as 25% of infants who have undergone DHCA Neurologic morbidity includes seizures, strokes, changes in tone and mental status, motor disorders, abnormal cognitive functioning, and postpump choreoathetosis Areas most vulnerable for ischemic injury include the neocortex, hippocampus, and striatum EFFECTS OF CPB Pulmonary effects Lung injury is mediated in one of two ways Leukocyte and complement activation cause an inflammatory response A mechanical effect leads to surfactant loss and atelectasis with resultant ventilation/perfusion mismatch, loss of lung volumes, and altered mechanics of breathing Pulmonary function after CPB is characterized by : A reduction in static and dynamic compliance Reduced functional residual capacity And an increased alveolar-arterial (A-a) gradient EFFECTS OF CPB Pulmonary effects Atelectasis and increased capillary leak due to hemodilution, and hypothermic CPB are the most likely etiologies Hemodilution reduces oncotic pressure → extravasation of fluid into the lung parenchyma Hypothermic CPB activates complement and leukocyte degranulation → capillary -alveolar membrane injury and platelet activation → microvascular dysfunction through platelet plugging and release of mediators → ↑PVR Modified ultrafiltration is highly effective in reducing lung water and pulmonary morbidity during the postoperative period EFFECTS OF CPB Renal effects CPB → hypothermia, nonpulsatile perfusion, and reduced mean arterial pressure → production of renin, angiotensin, catecholamines, and antidiuretic hormone → renal vasoconstriction and reduced renal blood flow Studies have been unable to link low-flow, low-pressure, nonpulsatile perfusion with postoperative renal dysfunction Risk factors for postoperative renal dysfunction include Preoperative renal disease Contrast-related renal injury And profound post-CPB reduction in cardiac output EFFECTS OF CPB Renal effects In the period following CPB, 8% of patients have acute renal insufficiency as indicated by oliguria and increased creatinine levels After spontaneous urine output, diuretics are effective at inducing diuresis and reversing renal cortical ischemia associated with CPB, but their use does not alter the time to recovery of renal function EFFECTS OF CPB Renal effects GFR, creatinine clearance, & medullary concentrating ability ↓ in neonates and young infants → greater fluid retention > older children and adult patients → ↑ total body water, ↑ organ weight (e.g., lungs, heart), ↑ difficulty with postoperative weaning from ventilatory support The use of ultrafiltration during rewarming or after CPB → ↓ total body water, limiting the damaging effects of CPB, & ↓ the postoperative ventilation period EFFECTS OF CPB EFFECTS OF CPB ... Infusion Types Antegrade: Infusion into the aortic root 2.Directly into the coronary arteries and / or bypass grafts Retrograde perfusion via the coronary sinus Combined Retrograde/Antegrade Infusion