7.8.1 What to do in case of acute problem?

ECC is a complex system (Figure 7.3) where critical incidents are frequent, despite all safeguards technology has developed. Acute problems occur in 0.4 - 1% of CABGs [1,2,3]. They can be life-threatening for the patient and often catch the medical team offguard. It is good to know the most serious ones, so that one can react appropriately would they occur in the operating room.

Hypotension at start of ECC

Haemodilution, the decrease in blood viscosity and the loss of the pulsatile regime decrease blood pressure at pump start. Typically, MAP will fall to 50 mmHg at this time. If it decreases until 30 mmHg, the problem is serious.

  • Check the pressure sensor, zero the artery, aspirate and flush the line.
  • Unknown aortic insufficiency; check for regurgitation in the LV on TEE; clamping the aorta restores pressure.
  • Left-to-right shunt through an unknown ductus arteriosus or through a L-R shunt (Blalock, aortopulmonary collaterals, AV fistula); clamp the shunt.
  • Extreme vasoplegia; anaphylactic shock (aprotinin, colloid), septic shock (endocarditis); increase flow, neosynephrine, noradrenaline infusion.
  • Aortic dissection: pressure wave disappears on arterial catheter while pressure is high on arterial bypass cannula; ascending aorta becomes puffy and purplish; wean off ECC immediately
  • Reverse connection of the bypass cannulae; blood is drawn from the aorta through the venous cannula; clamp the tubes and stop the machine.

Massive gas embolism

Air enters massively, most commonly via the venous reservoir, by defusing venous return. Lesser amounts may also come from suction, cardioplegia, oxygenator or disconnections; air may also pass from the RA to the LA through a patent foramen ovale or be drawn into the left heart if the patient has diaphragmatic movements while the LV or LA is open.

  • Air in arterial line and aorta; signs of cerebral and myocardial ischaemia; empty vessel.
  • Discontinue bypass, forced Trendelenburg position, debulking of aorta, 100% O2 ventilation2 .
  • Retrograde (1-2 L/min) hypothermic (20-24°) perfusion through the superior vena cava to perfuse the retro brain and drain air that has infiltrated the arterial side.
  • Resume normal bypass surgery after complete depletion of air; maintain high perfusion pressure and hypothermia at 20-24°C.
  • Brain protection: thiopental, mannitol, methylprednisolone, magnesium.
  • Brain scan or MRI as soon as possible.

Air in the left cavities

When the left cavities are open, air is derived from aspirations, incomplete purging of the left cavities before the aorta is unclamped, passage from the RA to the LA through a patent foramen ovale, diaphragmatic inspirium while the left cavities are open. Cavitation (pressure drop in the vortexes) and temperature changes decrease the solubility of blood gases, which then enter the gas phase and form minibubbles that accumulate under the overhangs.

  • Amplified Trendelenburg position, rolling of the operating table.
  • Hyperinflation of the lungs to expel accumulated air from the pulmonary veins.
  • Continuous suction (100-500 mL/min) through the cardioplegia cannula into the root of the aorta or through venting from the
  • Drainage by direct puncture of the cavity (LA, RV) with a syringue.
  • Heart shaking and manipulation.
  • Inotropic stimulation and high perfusion pressure (≥ 80 mmHg).
  • If debulking not possible: return to ECC.

Coronary embolism

Since RCA (and bypass grafts) are located at the zenith of the aorta in  supine position, air frequently collects there. 

  • ST segment elevation or undershoot in D II; acute RV dysfunction on TEE and in the surgical field; elevated VCP and hypotension.
  • Direct puncture of the air in the vessels with a fine needle.
  • Postpone protamine.
  • If major dysfunction (right akinesia), return to bypass after administration of heparin. Support for 15-20 minutes is usually enough to normalise the situation.
  • If right-sided failure is moderate, increase coronary perfusion pressure: infusion of nor-adrenaline and dobutamine.

Hypoxemia in ECC

Hypoxaemia is related to a defect in the O2 supply (mixer, disconnection), to a defect in the oxygenator, or to excessive desaturation of venous blood (low flow, low haematocrit, excessive consumption, hyperthermia). Insufficient heparinisation or massive transfusions may lead to partial thrombosis of the oxygenator.

  • Dark arterial blood in the aortic cannula; PaO2 < 100 mmHg, SvO2 < 55%.
  • Check the oxygenator connections (wall socket, hoses, fixing, leakage) and FiO2
  • At the beginning of the bypass: ventilation at 100% O2 and immediate weaning off pump.
  • During ECC: cool to 20°C to allow ECC to be interrupted and the oxygenator changed for a new one.
  • Call for help to prepare a new circuit.
  • Deep curarisation to reduce muscle O2

Circuit thrombosis

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, unchecked administration of protamine, or use of cardiotomy suctions after neutralisation of heparin by protamine.

  • At the beginning of the bypass: ventilation at 100% O2 and immediate weaning off
  • During ECC: cool to 20°C to allow ECC to be interrupted and the oxygenator changed.
  • Clamp the venous and arterial cannulas.
  • Call for help to prepare a new circuit.

 

© 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. KURUSZ M. Lessons from perfusion surveys. Perfusion 1997; 12:221-8
  3. MEJAK BL, STAMMERS A, RAUCH E, et al. A retrospective study on perfusion incidents and safety devices. Perfusion 2000; 15:51-9