7.5.5 Critical incidents and accidents during ECC

 Acute problems occur in 0.4 - 1% of CABGs [1,3,4]. The most dangerous events are aortic dissection, gas embolism, oxygenation failure and circuit thrombosis (see also What to do in case of  acute problem? ).

• Dissection of the aorta occuring at the start of ECC  is due to accidental intraparietal cannulation. There is an immediate disappearance of the pressure wave on the patient arterial catheter while the pressure is high on the arterial bypass cannula, and a very poor venous return to the machine is observed; the ascending aorta becomes blistered and purplish. Treatment is immediate : off pump manoeuvre. This incident is prevented by checking that the pressure curve is normal and pulsatile on the arterial bypass cannula before starting the machine.
• Reversal of arterial and venous cannulation: the aorta is drained of blood while the RA is inflated under pressure. The major risk is the accumulation of air in the aorta, which will embolise when the circulation is restored. The machine should be stopped immediately, the patient placed in the Trendelenburg position, the aorta drained and the procedure followed as for gas embolism.
• Gas embolism can occur at any time. Air enters the circuit through the venous reservoir, suctions, cardioplegia, oxygenator, filters or disconnections; bubbles form locally when the pressure suddenly drops at a point in the circuit (cavitation), or when blood temperature rises (decrease in solubility of gases). Air pockets form in the left heart chambers when these are opened in the operating field. Air can pass from the RA to the LA through a patent foramen ovale. Ambient air is drawn into the left heart if the patient has diaphragmatic movements while the LV or LA is open.
• The presence of air in the arterial cannula requires immediate action:
  • Off pump manoeuvre;
  • Forced Trendelenburg position to reduce the risk of airflow entering the carotid arteries;
  • Debulking of the aorta, hypothermic (20-24°) retrograde perfusion (1-2 L/min) through the superior vena cava to perfuse the brain a retro and drain the air that has infiltrated the arterial side;
  • Resume normal ECC after complete air emptying;
  • Administration of mannitol and steroids;
  • CT or MRI scan as soon as possible.
• Hypoxaemia is linked to a defect in the O₂ supply (mixer, disconnection), to a defect in the oxygenator, or to excessive desaturation of the venous blood (low flow, haematocrit too low, excessive consumption, hyperthermia). Curarisation can reduce muscle O₂ consumption by 30% when SvO₂ and/or ScO₂ are too low [2].
• The obstruction of the venous return allows only enough time to empty the reservoir to be faced with a machine that is automatically stopped by the pump's servo-control of the reservoir's blood level. Venous blockage is caused by air in the venous cannulae ("air lock"), inadequate positioning of the cannulae, manipulation of the heart or obstruction of the cannula by the atrial wall in the event of aspiration (vacuum-assisted venous return). The pump speed should be reduced immediately to avoid interruption, the reservoir refilled with lactated Ringer's and the cannulas repositioned.
• If the main pump fails, the arterial and venous circuit must be clamped immediately and a back-up pump used. Manual resumption is possible in the event of a power failure, but it is exhausting and does not allow the flow to be maintained for very long.
• Circuit thrombosis is a catastrophic event that requires interruption of the bypass to immediately change the reservoir, oxygenator and filters. It is caused by insufficient heparinisation, unintended administration of protamine, or the use of cardiotomy suctions after neutralisation of heparin by protamine. For this reason, a number of rules are strictly observed in bypass surgery: frequent checks of the ACT, preparation of protamine at the time of use and never in advance, suctioning through the CellSaver™ as soon as protamine is started after bypass surgery, since the machine must remain functional in case return on bypass is required.

There is still a long list of all possible failures and accidents that may occur during extracorporeal circulation: mechanical pump failure, electrical failure, disconnections, filter occlusion, etc.

 © CHASSOT PG, GRONCHI F, April 2008, last update, December 2019

References

1. DEPOIX JP, BERROETA C, PAQUIN S. Practical conduct in extracorporeal circulation. In: JANVIER G, LEHOT JJ (ed). Extracorporeal circulation: principles and practice, 2nd edition. Paris, Arnette Groupe Liaison SA, 2004, 571-80
2. IRISH CL, MURKIN JM, CLELAND A, et al. Neuromuscular blockade significantly decreases systemic oxygen consumption during hypothermic cardiopulmonary bypass. J Cardiothorac Vasc Anesth 1991; 5:132-7
3. KURUSZ M. Lessons from perfusion surveys. Perfusion 1997; 12:221-8
4. MEJAK BL, STAMMERS A, RAUCH E, et al. A retrospective study on perfusion incidents and safety devices. Perfusion 2000; 15:51-9