Lecture Notes: General Surgery

Harold Ellis, Sir Roy Calne, Christopher Watson

Self-assessment Questions

11 The heart and thoracic aorta

  • 1. How important was the development of cardiopulmonary bypass? What type of operations on the heart were possible before this?

    Correct answer:

    Prior to the development of cardiopulmonary bypass, surgery on the heart was limited to procedures that could be performed rapidly on a beating heart, such as mitral valvotomy to relieve mitral stenosis, where a finger is passed blindly through the left atrial appendage and through the stenotic mitral valve.

  • 2. What happens to the body when the circulation is temporarily stopped at body temperature? Which tissues are the least tolerant to ischaemia?

    Correct answer:

    If the circulation is temporarily stopped at normal body temperature, organs suffer ischaemic damage owing to lack of oxygen, the extent varying according to the metabolic demand of the organ. The brain is the most sensitive tissue in this respect and is liable to irreversible changes after 3 minutes of ischaemia. The spinal cord is next, followed by heart muscle, which will tolerate between 3 and 6 minutes of ischaemia at normal temperature.

  • 3. How long can the heart muscle survive ischaemic conditions before it is irreversibly damaged? (At body temperature)

    Correct answer:

    Between 3 and 6 minutes.

  • 4. What is the effect of hypothermia on the tolerance of the body tissues to ischaemia?

    Correct answer:

    The tolerance to ischaemia can be increased slightly by lowering the metabolic rate by hypothermia; at 28°C up to 10 minutes of circulatory arrest can be tolerated.

  • 5. What has been possible with the development of cardiopulmonary bypass?

    Correct answer:

    It is now possible to stop the heart for prolonged periods while a machine is used to take over the pumping and oxygenation of the blood. Generally, a combination of hypothermia and cardiopulmonary bypass is used.

  • 6. What is the technique of cardiopulmonary bypass? What is the role of ‘cardioplegic’ solution?

    Correct answer:

    After full heparinization, cannulae are inserted into the venae cavae via the right atrium to siphon off the venous return from the systemic circulation. The blood is then pumped through an oxygenator and a heat exchanger before returning to the systemic circulation via a catheter in the ascending aorta or the femoral artery. This form of bypass will perfuse the whole body with oxygenated blood at an adequate pressure while diverting it from the heart and the lungs. The heart may now be stopped and cooled by infusion via the coronary arteries of cold ‘cardioplegic’ solution containing potassium, to produce rapid cardiac arrest in diastole. If the aorta is cross-clamped, the heart may be opened in a bloodless field with access to all chambers.

  • 7. What is ‘cardioplegic’ solution used for?

    Correct answer:

    The heart may be stopped once on cardiopulmonary bypass and can be cooled by infusion via the coronary arteries of cold ‘cardioplegic’ solution containing potassium, to produce rapid cardiac arrest in diastole.

  • 8. How does ‘cardioplegic’ solution work?

    Correct answer:

    This cold solution is infused via the coronary arteries. It contains potassium so produces a rapid cardiac arrest in diastole.

  • 9. What are the three main complications of cardiopulmonary bypass?

    Correct answer:

    (1) Emboli. (2) Haemorrhage. (3) Hypothermic injury and ischaemia.

  • 10. What is the effect of emboli following cardiopulmonary bypass?

    Correct answer:

    Air entrapped during formation of the bypass circuit or entering during bypass, or thrombus forming in the bypass circuit, may embolize into the cerebral and peripheral circulation with catastrophic results.

  • 11. What is the effect of haemorrhage following cardiopulmonary bypass?

    Correct answer:

    Haemorrhage postoperatively may result in cardiac tamponade. Passage through the bypass circuit activates the clotting cascade and consumes platelets, thus increasing the risk of haemorrhage.

  • 12. What is the effect on the blood as it passes through the cardiopulmonary bypass circuit?

    Correct answer:

    Passage through the bypass circuits activates the clotting cascade and consumes platelets, thus increasing the risk of haemorrhage.

  • 13. What is the effect of hypothermic injury and ischaemia following cardiopulmonary bypass?

    Correct answer:

    This may result in pancreatitis and contribute to the occurrence of peptic ulceration and mesenteric ischaemia.

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