Cardiopulmonary Bypass

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Cardiopulmonary Bypass
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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)

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Adult Cardiac Surgery
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Heart - coronary artery bypass (diagram)
                                                  
                                                  
                                                  
                                    
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The Heart-Lung machine

• Venous cannulae
• Venous reservoir
• Oxygenator/Heat exchanger
• Pump
• Arterial line filter
• Arterial cannula
• Cardiotomy suction
• Cardioplegia delivery system

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Venous Reservoir

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

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Oxygenator

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

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Heat Exchanger

• Also called the heater / cooler
• Controls perfusate temperature
• Warm and cold

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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

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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

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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)

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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

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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

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Myocardial Protection

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

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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

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Function of Cardioplegic Protection

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

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Termination of Perfusion

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

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Complications of Cardio- Pulmonary Bypass

• Duration of bypass
• Age
• Cardiac function

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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.
• KidneyPreoperative renal status and periods of
  low cardiac output after CPB are the most
  important predictors of post-op renal function.
• GILiver dysfunction. Pancreatitis. GI bleeding.
  Mesenteric ischaemia due to vasculitis.

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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.

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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

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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

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IABP Background

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

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Myocardial Oxygen Consumption

• Has a linear relationship to
• Systolic wall stress
• Intraventricular pressure
• Afterload
• End diastolic volume
• Wall thickness

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IABP in Myocardial Infarction and Cardiogenic
Shock

• Improves diastolic flow velocities after
  angioplasty
• Allows for additional intervention to be done
  more safely

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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

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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

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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
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Timing of Counterpulsation

• Electrocardiographic
• Arterial pressure tracing

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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