Case of the Month #11 - VV ECMO

roubleshooting the hypoxaemic patient involves reviewing the patient, the circuit and their interaction.

Circuit

1. Maximise circuit blood flow: increasing extracorporeal blood flow will improve oxygenation (relative to cannula size) but may increase recirculation. High blood flow causes excess negative pressure in the vessel and increases risk of haemolysis. An additional drainage cannula can be considered if flow inadequate.
2. Reduction or loss of circuit flow: ensure intravascular volume is maintained and exclude any kink in circuit or obstruction from high intra-abdominal or intra-thoracic pressure (ie pneumothorax). Cannula position may need to be manipulated to increase flow.
3. Minimise recirculation: identified by minimal colour change between access and return lines and high pre-oxygenator saturations. Cannula manipulation may be required.
4. Failing oxygenator: rising transmembrane pressure or reduced gas exchange (falling post oxygenator saturations) can indicate thrombus within the circuit. A circuit change may be required.
5. Sweep gas flow: ensure oxygen supply is connected and set at FiO₂ 1.0

Patient

1. Reducing oxygen consumption: temperature control to 36°C using heat exchanger, increasing sedation and use of neuromuscular blockade.
2. Reducing cardiac output: beta blockade (ie esmolol) can  reduce the proportion of venous return that does not enter the membrane lung and subsequently improve arterial oxygenation. High cardiac output is often seen in septic patients.
3. Increasing oxygen delivery: blood transfusion to increase haemoglobin content.
4. New or worsening lung problem: pulmonary haemorrhage, pneumothorax and progressive consolidation can all occur. Intervention may be required but is associated with a significant risk of bleeding therefore a conservative approach is taken.
5. Optimising mechanical ventilation: ventilator settings or FiO₂ may need to be increased to improve arterial oxygenation.