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Cardiopulmonary Bypass

Cardiopulmonary Bypass. Cardiac surgery. Coronary revascularisation (On and off pump) Valvular heart disease Surgery for heart failure Transplantation and assist devices Congenital and GUCH surgery Minimally invasive techniques Re-do surgery

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Cardiopulmonary Bypass

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  1. Cardiopulmonary Bypass

  2. Cardiac surgery • Coronary revascularisation (On and off pump) • Valvular heart disease • Surgery for heart failure • Transplantation and assist devices • Congenital and GUCH surgery • Minimally invasive techniques • Re-do surgery • Miscellaneous (trauma, tumours, aneurysms, septal defects, pericardiectomy, embolectomy, dissections)

  3. Adult Cardiac Surgery

  4. Heart - coronary artery bypass (diagram)

  5. The Heart-Lung machine • Venous cannulae • Venous reservoir • Oxygenator/Heat exchanger • Pump • Arterial line filter • Arterial cannula • Cardiotomy suction • Cardioplegia delivery system

  6. Venous Reservoir • Siphons blood by gravity • Provide storage of excess volume • Allows escape of any air bubbles returning with the venous blood

  7. Oxygenator • Provides oxygen to the blood • Removes carbon dioxide • Several types • Bubble oxygenator • Membrane oxygenator • Microporous hollow-fiber oxygenators

  8. Heat Exchanger • Also called the heater / cooler • Controls perfusate temperature • Warm and cold Q10

  9. Cardiopulmonary Bypass • Heparinization • Total bypass • Partial bypass • Flowrates 2-2.5 l/min. per square meter • Flowrates depend on body size • Flowrates depend on cannula sizes • Hypothermia

  10. Shed Blood • Is aspirated with a suctioning apparatus, filtered and return to the oxygenator • A cell saving device may also be utilized during and after bypass

  11. Blood Pressure • Decreases sharply with onset of bypass (vasodilatation) • Mean arterial pressure needs to the above 50-60 mm Hg. • After 30 minutes perfusion pressure usually increases (vasoconstriction)

  12. Oxygen and Carbon Dioxide Tensions • Concentrations are periodically measured in both arterial and venous lines • Arterial oxygen tension should be above 100 mm Hg • Arterial carbon dioxide tensions should be 30-35 mm Hg • A drop in venous oxygen saturation suggests underperfusion

  13. Acid-Base Regulatory Strategy • pH-stat strategy • Aim ; constant pH, • Total CO2 ; increased • Intracellular state ; acidosis • Alpha-stat strategy • Aim; constant OH/H, • Total CO2 ; constant , • Intracellular state ; neutral

  14. Myocardial Protection • Cold hyperkalemic solutions • Produces myocardial quiescence • Decreases metabolic rate • Provides protection for 2-3 hours • Blood vs. crystalloid

  15. Chemical Principles Inducing Cardiac Arrest • Myocardial depletion of calcium • Myocardial depletion of sodium • Elevation of extracellular sodium • Elevation of extracellular magnesium • Infusion of local anesthetic agents • Infusion of calcium & antagonistics

  16. Function of Cardioplegic Protection • 1. Electromechanical arrest • 2. Function of temperature effect • 3. Function of oxygen content • 4. Substrate enhancement • 5. Buffering capacity

  17. Termination of Perfusion • Systemic rewarming • Flowrates are decreased • Hemodynamic parameters • Venous line clamping • Pharmacologic support • Neutralization of heparin

  18. Complications of Cardio- Pulmonary Bypass • Duration of bypass • Age • Cardiac function

  19. Organ dysfunction after bypass • Heart: C3a and endothelin cause coronary constriction. Oedema reduces contractility. • Lung: Complement increases pulmonary capillary permeability. Composition of alveolar surfactant changes. Pulmonary compliance decrease. Pain inhibits respiration. • CNS: Incidence of stroke 1-5%. Subtle neurological injuries up to 50% of patients. • Kidney:Preoperative renal status and periods of low cardiac output after CPB are the most important predictors of post-op renal function. • GI:Liver dysfunction. Pancreatitis. GI bleeding. Mesenteric ischaemia due to vasculitis.

  20. Open Heart Surgery • Neurologic injury • Neurologic injury is the second most common reason for death in open heart operations • Significant neurologic injury was observed in 2% to 5% of patients, whereas mild cognitive dysfunction was seen in 70% of patients in the early stage • Extracorporeal circulation does not cause changes in brain blood circulation, but hemodilution and decrease in oncotic pressure lead to edema in the brain and in other organs • Cerebral ischemia due to microemboli or macroemboli, systemic inflammatory response, and cerebral hypoperfusion during cardiopulmonary bypass (CPB) causes impairment in the blood brain barrier.

  21. Optimal Neurologic Protection • Variables • Perfusion pressure • Flow rate • Duration of cooling • Duration of circulatory arrest • Hematocrit • Ultrafiltration • Blood gas strategy • Presence of collateral flow • Impact of age

  22. Postpump Syndrome on Lung • Characteristics • Increased alveolo-arterial gradient (A-aDO2) and intrapulmonary shunt • Decreased pulmonary compliance • Increased pulmonary vascular resistance • Increased pulmonary vascular perrmeability

  23. IABP Background • Preload • Afterload • Coronary flow • Myocardial oxygen consumption in the heart is determined by: • Pulse rate • Transmural wall stress • Intrinsic contractile properties

  24. Myocardial Oxygen Consumption • Has a linear relationship to: • Systolic wall stress • Intraventricular pressure • Afterload • End diastolic volume • Wall thickness

  25. IABP in Myocardial Infarction and Cardiogenic Shock • Improves diastolic flow velocities after angioplasty • Allows for additional intervention to be done more safely

  26. IABP During or After Cardiac Surgery • Patients who have sustained ventricular damage preoperatively and experience harmful additional ischemia during surgery • Some patients begin with relatively normal cardiac function an experienced severe, but reversible, myocardial stunning during the operation

  27. Other Indications for IABP • Prophylactic use prior to cardiac surgery in patients with: • Left main disease • Unstable angina • Poor left ventricular function • Severe aortic stenosis Contraindications to IABP • Severe aortic insufficiency • Aortic aneurysm • Severe ilio-femoral vessel disease

  28. Insertion Techniques • Percutaneous • sheath less • Surgical insertion Positioning The end of the balloon should be just distal to the takeoff of the left subclavian artery Position should be confirmed by fluoroscopy or chest x-ray

  29. Timing of Counterpulsation • Electrocardiographic • Arterial pressure tracing

  30. Complications • Limb ischemia • Thrombosis • Emboli • Bleeding and insertion site • Groin hematomas • Aortic perforation and/or dissection • Renal failure and bowel ischemia • Neurologic complications including paraplegia • Heparin induced thrombocytopenia • Infection

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