Cardiopulmonary Bypass

Question 1

Adverse effects of CPB circuit

Answer 1

• Activation of blood components and cytokine release (synthetic interface of circuit)
  
  • Membrane oxygenator exerts most damage on blood components
• Precipitation of cold agglutinins with cooling on bypass
  
  • If recognized, attempts should be made to do procedure under normothermia

Question 2

Myocardial protection of arrested heart is achieved in 3 ways

Answer 2

1. Electrochemical silence
2. Hypothermia
3. Lack of distention

Question 3

Methods of cardioplegia delivery

Answer 3

• Antegrade (Ao root or directly down coronary ostia/bypass grafts)
  
  • Quicker electromechanical arrest (30-60 seconds)
    
    • Delay usually indicates problem with delivery of solution (failure to completely cross clamp Ao or significant CAD) or unrecognized AI.
• Retrograde
  
  • Longer electromechanical arrest (2-4 minutes)
  • Imcomplete protectin of RV due to the delivery of cardioplegia behyond the sige of the posterior interventricular vein
  • Advantage: flushing air/emboli from coronaries

Question 4

MOA of cardioplegia

Answer 4

• Heart arrests in diastole and does not use ATP
• Cold fluid (~ 4 degrees C) cools heart, allowing slowing of metabolism

Question 5

Cardioprotective Q10 rule

Answer 5

For every 10 degree C drop in temperature, metabolic rate decreases by 50%

Question 6

Venous drainage on CPB is determined by what factors

Answer 6

• CVP
• Height differential between patient and venous reservoir
• Use of vacuum drainage
• Resistance in venous cannulae/tubing
• Absence of air within the system

Question 7

What is “chattering” during CPB

Answer 7

A result of venous wall collapase against the venous cannulae due to inadequate blood volume or excessive siphon pressure

Correction: volume

Question 9

Venous cannulation sites:

Answer 9

• Atriocaval (dualstage cannula)
  
  • Elevation of heart may king cavo-atrial junction resulting in poor drainage
• Bicaval
• Femoral or iliac vein
  
  • Emergency closed cardiopulmonary assist
  • Prevention or managment of bleeding during reoperative sternotomy
  • Aortic dissection or aneurysm repair
  • Applications of CPB that do not require sterontomy or thoracotomy
    
    • Minimally invasive valve surgery

Question 10

Complications of venous cannulation

Answer 10

• Atrial arrhythmia (SA node injury)
• Atrial or caval injury/tear
• Air embolization
• Injury due to catheter malposition
• Reversing of arterial and venous lines
• Unexpected decannulation
• Obstruction of cavae with tying of improperly placed purse-string sutures
• Laceration of nearby benous branches/vessels/cava with caval tapes during bicaval cannulation

Question 11

Arterial cannulation sites/options

Answer 11

• Ascending Aorta
• Innominate artery
• Distal aortic arch
• Axillary/subclavian artery
• Femoral/external iliac artery

Question 12

Complications of arterial cannulation

Answer 12

• High velocity jets (sandblasting effect)
  
  • Damage Ao wall
  • Dislodge atheroemboli
  • Produce Ao dissection
  • Distrub flow to nearly vessels
  • Cause cavitation
  • Hemolysis
• Ao debris preferentially directed into left common carotid (left sided stroke)
• Difficult insertion
• Bleeding
• Intramural / malposition of cannula tip
• Failure to remove air from arterial line
• Injury to Ao back wall
• Obstruction of flow
• Inadequate cerebral perfusion
• Delated complications

Question 13

Best method for assessing atherosclosis of Asc Ao

Answer 13

Epiaortic ultrasound

Question 14

Porcelain aorta frequency

Answer 14

1.2% - 4.3% of cases

Indication for alternative cannulation site or consideration of off-pump surgery

(may have to replace Asc. Aorta)

Question 15

Frequency of Aortic Dissection as a complication of Arterial Cannulation

Answer 15

0.01% - 0.09%

More common with pateints with Ao Root disease

• Clues:
  
  • Blue discoloratin beneath adventitia near the cannulation site
  • Increase in arterial line pressure
  • Sharp reduction in return to venous reservoir

Question 16

Response to acute Ao Dissection after Ao cannulation

Answer 16

• Stop pump
• Leave cannula in place
• Prompt re-cannulation of alternative site (innominate, axillary, true lumen distal, femoral)
• Control BP medically
• Cool pateint to 18 degrees C
• DHCA
• Open aorta at original site of cannulation and repair/replace (including site of injury) aorta

Question 17

Outcomes following acute Ao Dissection after Ao Cannulation

Answer 17

Survival rates (66-85%) if recognized early

Surival 50% if recognized after surgery

Question 18

Complications of lower body arterial cannulation

Answer 18

• Arterial injury
• Dissection
• Late stenosis / thrombosis
• Bleeding
• Lymph fistula
• Groin infection
• Cerebral and Coronary atheroembolism
• Malperfusion
• LE ischemia (due to prolonged retrograde perfusion)
  
  • Avoided by use of side-arm distal perfusion cannulae

Question 19

Most serious complicaiton of lower body (groin) arterial cannulation

Answer 19

Retrograde arterial dissection

• May extend in retrograde fashion all the way to Ao root
• Incidence: 0.2-1.3%
• Mortality: 50%
• More likely to occur in diseaesd arteries in patients > 40 yo
• Confirmed by echocardiography of descending thoracic Ao

Question 20

Cardiac disstention on CPB can occur due to these factors:

Answer 20

• Blood escaping from arterial or venous cannulae (poor drainage)
• Coronary sinus or Thebesian venous return (via pulmonary circulation)
• Bronchial arterial and venous blood
• AV insufficiency
• Other abnormal sources (PFO/PDA)

Question 21

4 most commonly used vents during CPB to avoid cardiac distention

Answer 21

1. Aortic root vent (i.e. DLP)
2. LV vent (most commonly via right superior pulmonary vein)
3. LV vent (via apex)
4. Main PA vent (no valves in pulmonary circulation)

Question 22

Frequency of Persistent Left Superior Vena Cava (PLSVC)

Answer 22

0.3-0.5% of population

Question 23

Drainage characteristics and CPB implications of PLSVC