Cardiopulmonary Bypass/Myocardial Protection Flashcards
Adverse effects of CPB circuit
- 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
Myocardial protection of arrested heart is achieved in 3 ways
- Electrochemical silence
- Hypothermia
- Lack of distention
Methods of cardioplegia delivery
- 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.
- Quicker electromechanical arrest (30-60 seconds)
- 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
MOA of cardioplegia
- Heart arrests in diastole and does not use ATP
- Cold fluid (~ 4 degrees C) cools heart, allowing slowing of metabolism
Cardioprotective Q10 rule
For every 10 degree C drop in temperature, metabolic rate decreases by 50%
Venous drainage on CPB is determined by what factors
- CVP
- Height differential between patient and venous reservoir
- Use of vacuum drainage
- Resistance in venous cannulae/tubing
- Absence of air within the system
What is “chattering” during CPB
A result of venous wall collapase against the venous cannulae due to inadequate blood volume or excessive siphon pressure
Correction: volume
Venous cannulation sites:
- 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
Complications of venous cannulation
- 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
Arterial cannulation sites/options
- Ascending Aorta
- Innominate artery
- Distal aortic arch
- Axillary/subclavian artery
- Femoral/external iliac artery
Complications of arterial cannulation
- 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
Best method for assessing atherosclosis of Asc Ao
Epiaortic ultrasound
Porcelain aorta frequency
1.2% - 4.3% of cases
Indication for alternative cannulation site or consideration of off-pump surgery
(may have to replace Asc. Aorta)
Frequency of Aortic Dissection as a complication of Arterial Cannulation
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
Response to acute Ao Dissection after Ao cannulation
- 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
Outcomes following acute Ao Dissection after Ao Cannulation
Survival rates (66-85%) if recognized early
Surival 50% if recognized after surgery
Complications of lower body arterial cannulation
- 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
Most serious complicaiton of lower body (groin) arterial cannulation
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
Cardiac disstention on CPB can occur due to these factors:
- 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)
4 most commonly used vents during CPB to avoid cardiac distention
- Aortic root vent (i.e. DLP)
- LV vent (most commonly via right superior pulmonary vein)
- LV vent (via apex)
- Main PA vent (no valves in pulmonary circulation)
Frequency of Persistent Left Superior Vena Cava (PLSVC)
0.3-0.5% of population
Drainage characteristics and CPB implications of PLSVC
Advantages of Microplegia
Advantages of retrograde cardioplegia?
Advantages of blood cardioplegia?
Describe the neurohormonal response while on CPB?
Describe cerebral blood flow while on cardiopulmonary bypass?
CPB Vasoplegic Syndrome
Disadvantages of retrograde cardioplegia?
characteristics of hibernating myocardium?
Myocardial ischemia effect on conduction cells of the heart.
Myocardial protection strategies for an ischemic heart?
Pump flow minimums based on body temperature?
Steps in antegrade cerebral perfusion?
Characteristics of Stunned Myocardium?
What is the warming/cooling gradient allowed on CPB?
