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Cardiopulmonary Bypass

last updated: November 25, 2016

Orlando Debesa

After cardiac surgery involving the cardiopulmonary bypass machine, one of your main tasks is to treat cardiac dysfunction. The cardiac dysfunction occurs secondary to the ischemia the heart undergoes (regardless of hypothermia and cardioplegia, the heart is never totally protected). This is part of the reason why post cariac surgery, patients come out on pressors. 

Pathophysiology

During cardiopulmonary bypass and cardiac ischemia, the Na/K pump stops working properly, allowing sodium to remain inside the cell and water entering the cell(s) causing swelling and edema.  This is partly  the reason why diuretics are important during the resuscitative phase; the other reason is because a lot of fluid is given to these patients in the OR. 

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  • Immune Dysfunction

    • postoperative immunosuppression and impaired pulmonary function​

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  • Pulmonary Dysfunction

    • associated with anomalies in gas exchange, alterations in lung mechanics, or both​

    • anomalies in gas exchange are evidenced by a widening of the alveolar-arterial oxygen gradient

    • increased microvascular permeability in the lung,[12] 

    • increased pulmonary vascular resistance,[4] 

    • increased pulmonary shunt fraction,[5] and

    • intrapulmonary aggregation of leukocytes and platelets

    • some recent studies suggest that retrieval of the internal mammary artery, which typically necessitates pleural dissection, may contribute 

    • phrenic nerve injury

      • hypothermia usually causes this​

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  • Anesthesia Dysfunction + prolong supine position = ventilation/perfusion mismatch

    • results in an upward shift of the diaphragm

    • relaxation of the chest wall

    • altered chest wall compliance

    • shift in blood volume to the abdomen from the thorax​

Non cardiopulmonary bypass patients tend to be on the dryer side because not a lot of fluid is given to them in the operating room and thus cardiac dysfunction is rarely seen. 

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Hypotension Differential Diagnosis

  • left ventricular dysfunction

  • vasodilatory shock

  • arrhythmias

  • diastolic dysfunction

  • right ventricular dysfunction

  • arterial air embolization

  • surgical / technical problems

  • left ventricular outflow tract obstruction

  • airway obstruction

  • bleeding

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Immediatly post cardiac surgery, it is very difficult to obtain ECHOcardogram pictures secondary to air in the mediastinum (remember, air is the enemy of ultrasound). 

Cardioplegia

Both antegrade and retrograde should always be used. If the procedure is short enough (eg. aortic valve replacement) some surgeons will just do antegrade cardioplegia. 

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Thick hearts are more difficult to protect and stunning is a big problem in the first 24 hours. Keep on Epi 0.02 for approximately 24 hours and use norepinephrine for blood pressure. Thick ventricles can also have increased ectopy - amio for 6 weeks in recommended by some. 

CPB has two reservoirs:

1) venous reservoir (receives blood from venous drainage)

2) cariotomy reservoir (receives blood from the operative field)

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Vacuum-assisted drainage in cardiopulmonary bypass

- emerged in an attempt to reduce the deleterious effects of hemodilution (reducing the prime volume)

- uses negative pressure in the venous reservoir (eliminating gravity and siphoning)  

Cardiopulmonary Bypass

 

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Anemia

 

Thrombocytopenia

 

Coagulopathy

 

Electrolyte abnormalities

  • hypocalcemia

  • hypokalemia

  • hyperkalemia

  • hypomagnesemia

 

Hyperglycemia

 

Hypothermia

 

Sternal closure

 

Treatment

  • correct above abnormalities

  • IABP

  • ECMO

  • VAD

 

References

UpToDate, October 6, 2015, Weanign from Cardiopulmonary Bypass

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