Illustration of recirculation in a patient on veno-venous ECMO. The oxygenated blood returned to the patient is immediately aspirated by the ECMO circuit.
In a system with two drainage cannulas, it is obvious that the blood in one drainage tubing has the same colour as the blood returned to the patient, indicating recirculation.
Monitoring the patient on veno-arterial ECMO
In veno-arterial ECMO, the blood is taken from the venous circulation and returned to the arterial circulation. The end result is arterial blood with a higher O2 and lower CO2 content entering the systemic circulation.
Veno-arterial ECMO bypasses the cardiopulmonary circulation, and the risk of no flow in the pulmonary vessels is high. This may lead to thrombosis. In the absence of left ventricular ejection (which often occurs if the heart is weakened and its afterload is increased by the pressure generated by the ECMO), ventricular cavities will distend and thrombi are likely to be formed. It is therefore important to ensure that there is continuous blood flow through the lungs and no stagnation of blood in the cardiac cavities. Ensuring opening of the aortic valve is required, and this can usually be observed on the pressure waveform. Using a pulmonary artery catheter allows continuous monitoring of pulmonary blood flow. Changes in the pressure waveforms must be recorded and discussed, as they will reflect a change in one of many aspects in the patient’s care. The reasons for changes in the arterial pressure waves are listed in Table 4.1.
| Decreased pulsatility | Increased pump flow |
| Decreased heart contractility | |
| Pericardial collection | |
| Hypovolaemia | |
| Pneumothorax | |
| Aortic valve thrombosis | |
| Increased pulsatility | Decreased pump flow |
| Increased heart contractility |
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