CPB Hardware

What is the effect of non-pulsatile flow?

Initiates intrinsic coagulation pathway through activation of factor XII (12)

What activates fibrinolytic system?

Kallikrein

What is the function of bradykinin?

Increased capillary permeability and development of tissue edema

What system does CPB activate?

Complement system which activates recruitment of leukocytes

What does the release of cytokines cause?

Myocardial dysfunction

What is ischemia reperfusion?

Tissue damage caused when blood supply returns after a period of ischemia, worsening the injury

What causes platelet dysfunctions in CPB?

1. Hypothermia

2. Hemodilution

3. Cardiotomy suction

4. Platelet aggregate formation

5. Formation of platelet leukocyte complexes

6. Platelet adhesion to artificial surfaces

What are the various emboly produced during CPB?

1. Fibrin

2. Platelet aggregates

3. Neutrophilic RBC debris

4. Gaseous

5. Spallated materials

How does optimal cardiac output decrease systemic inflammatory response to CPB?

Clears inflammatory mediators

What is the function of aprotinin-serine protease inhibitor?

Decrease systemic inflammatory response to CPB

WHat is the function of modified ultrafiltraion?

Decreases tissue edema and circulating inflammatory properties

What factors can help decrease systemic inflammatory response to CPB?

1. Leukocyte depletion filters

2. Pulsatile perfusion

3. Coating of membranes and tubings with heparin

What is the function of venous cannulation?

Allows deoxygenated blood to be drained from the patient into the extracorporeal circuit

What type of cannulation is typically used for a CABG?

Two-stage venous cannula because it does not involve opening the chambers of the heart

What is bicaval cannulation?

Two single-stage cannulae sit in the inferior and superior vena cavae and are connected using a Y-connected to the venous line

What can also be used as a cannulation site for more complex sugrery?

Femoral veins

What cannulation is used for femoral veins?

An elongated single-stage cannula passed up the femoral vein into the vena cava

How do they select the size of a venous cannula?

To allow one third of total flow drain through SVC cannula and two third of total flow drain through IVC

What is a double stage venous cannula?

IT has a wider portion with holes in the section designed to sit in the RA and a narrower tip designed to rest in the IVC

What can the tips of cannulas be made of?

Plastic or metal

What is the point of the internal diameter to outer diameter ratio?

It is used to determine flow efficiency, ratios below 1 indicates potential flow restriction

What do venous cannulas look like?

What is cavoatrial venous cannulation with two-stage canula typically used in?

• Aortic valve procedures

• Coronary bypass procedures

• AVR+CABG procedures

• Bentall procedure

What is the disadvantage of two stage venous cannula?

It rewarms the heart which causes less myocardial protection

What is venous drainage accompanied by?

Gravity siphonage

Where should the venous reservoir be?

Below the level of the patient

What are the determinants of venous drainage?

• Height of the patient above venous reservoir

• Patient’s blood volume

• Resistance of tubing

• Cannula dimensions

What are causes of low venous return?

• Reduced venous pressure

• Inadequate height of patient above venous reservoir

• Malposition of venous cannula

• Obstruction or excess resistance of lines and cannula

• Kink/air lock

How to achieve augmented venous return?

• Placing a roller pump in venous line

• Centrifugal pump in venous line

• Vacuum assisted venous drainage

How do you achieve adequate venous drainage?

Speeds of 1000-2000 RPM of kinetic pump or application of 20 mmHg vacuum to venous

What are potential problems of augmented venous returnt?

• Hemolysis

• Collapse of right atrium resulting in impaired venous drainage and chattering of venous line

• Micro air aspiration

Where can peripheral cannulation be done?

• Femoral veins

• Iliac veins

• Less common used sites, innominate vein and axillary vein

What are indications of peripheral cannulation?

1. Emergency closed cardiopulmonary assist

2. Support of ill patients before induction of anesthesia

3. Before sternotomy for reoperations

4. Minimal access surgery

5. Certain aortic and thoracic surgery

What is arterial cannulation?

Delivers oxygenated blood from the heart-lung machine directly into the patient’s arterial system

How do they determine the size of the arterial cannula?

The size of the vessel that is being cannulated and blood flow required

What is the most common site of arterial cannulation?

Ascending aorta

How are arterial cannulas sized?

Internal diameter

What are the advantages of metal tipped cannula?

1. Provides best internal diameter to outer diameter ratio

2. Easy to cannulate

What are the advantages of metal tipped cannula?

1. Jet effect → Hemolysis

2. No side holes to reduce sandblast effect

3. Traumatic → may damage posterior intima

What is the jet effect?

hemolysis caused by high-velocity jets of blood flowing through narrow openings, often after cardiac repairs

What type of arterial cannulas provide the best flow?

Thin-walled wire-wound cannulas and are very resistant to kinking

What is the ideal flow with aortic cannulation?

<100 mmHg pressure gradient

What happens if pressure gradient is >100 mmHg with aortic cannulation?

Hemolysis and protein denaturation

When should you suspect aortic dissection?

• Increased CPB systemic line pressure

• Sudden decrease in both venous return or arterial pressure

• Decreased organ perfusion

• Blue discoloration of aortic root

• Bleeding from cannulation site

How do you manage aortic dissection?

• Prompt cessation of CPB

• Re-cannulation distal to dissection

• Induction of deep hypothermia and a period of circulatory arrest while aorta is opened and repiared

What does sandblasting effect cause?

Perioperative stroke, aortic dissection, and postoperative renal dysfunction

What is epiaortic ultrasonic scanning?

Used to detect atherosclerotic plaque in the ascending aorta

What should mean pressure be during arterial cannulation?

70-80 mmHg

What are indications for femoral cannulation?

1. Aneurysm of ascending aorta or diffuse atherosclerosis of ascending aorta

2. In unstable patients before induction

3. Reoperations

4. When antegrade dissection complicates aortic cannulation

5. Minimally invasive cardiac surgery

How do you determine length of tubing?

What is biomaterial tubing?

Binding heparin or other surface modifying agents into inner surface of the tubing may improve biocompatibility

What coats biomembrane mimicry?

Derivative of phosphorylcholine (memys,sorin)

What are the different heparin coated circuits?

1. Heprain bound to tubing is slowly released into circulation

2. Heparin is permanently bound covalently to biomaterial surface

3. Hybrid surface-combination of heparin releasing and heparin immobilized

What are surface modified additives for tubing?

Poly 2-methoxy-ethylacrylate which has hydrophobic properties and little tendency to react with blood products

What is the primary form of heat transfer?

Forced convection

When should you do cardiac venting?

Whenever the left ventricle is unable to handle the amount of blood that is returning to it

What is the purpose of cardiac venting?

1. Aid visualization and provide bloodless field

2. Avoid chamber distension

3. Reduce myocardial rewarming

4. Prevent cardiac ejection of air

What is cardiac venting?

A surgical technique used to remove blood and air from the heart chambers

What are potential sites of cardiac venting?

1. Pulmonary artery

2. Right superior pulmonary vein

3. Left atria

4. Left ventricle

5. Aortic root cardioplegia cannula

How do you monitor LV disension?

• PA Catheter (measures real time cardiovascular pressures and oxygen saturation)

• Left atrial monitoring line

• Transesophageal echocardiogram

How do you prevent air embolism during cardiac venting?

Heart is allowed to fill before vent insertion

What is the function of arterial filters?

Remove air and particulate matter

What are limitations of arterial filters?

• Relatively large volume required to prime the filters

• Hemolysis, platelet loss, complement activation

• Lack of proven benefit

• Paradoxical risk of increased particulate embolism

What is the function of leukocyte depletion filters?

Non-woven polyester fibers that have been surface modified to remove leukocytes

Which immune cells are an important contributor to ischemia reperfusion injury?

Neutrophils

What is left heart bypass?

Blood is removed from the left heart and placed into left atrium and the lungs provide gas exchange

(no oxygenator)

What is the risk of left heart bypass?

Air embolism

When do you use left heart bypass?

Descending thoracic or large thoracoabdominal aortic aneurysms

What does left heart bypass consist of?

Tubing and centrifugal pump (no reservir, heat exchanger, or bubble)

What are minimal extracorporeal circuits composed of?

• Single centrifugal pump

• Membrane oxygenator

• Surface modification

What is the priming volume for a minimal extracorporeal circuit?

500 mL

What are minimal extracorporeal circuits used for?

CABG, aortic, and mitral valve surgeries

What are the limitations of minimal extracorporeal circtuis?

• Air embolization

• Unable to handle excess venous return

• Lack of heat exchanger

• Need to use separate cell processing system

• Increased cost

What is dialysis?

Blood is separated from crystalloid solution or dialysate by a semipermeable membrane

What is ultrafiltration?

Movement of water across a membrane due to transmembrane pressure gradient

What is the function of ultrafiltration?

Removes excess fluid and results in increased hematocrit, decreased lung waters, and decreased tissue edema

What are the advantages of ultrafiltration?

• Conserve platelets and coagulation factors → improve perioperative hemostasis

• Conserve albumin → Reduce lung water and post operative ventilator support

What is conventional ultrafiltration?

Practice of withdrawing blood from the patient through venous reservoir during rewarming period and passing it through a hemoconcentrator and pumping it back into the patient through venous reservoir

What is zero balanced ultrafiltration?

Volume of plasma water removed is replaced by a balanced electrolyte solution to remove inflammatory mediators

What is modified ultrafiltration?

Withdrawing blood from the patient through aortic cannula and passing it through hemoconcentrator and it goes back into the patient through venous cannula

What are the comparisons of the ultrafiltration methods?