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Extracorporeal membrane oxygenation, or ECMO in short, is a technique to support the lung function of critically ill patients. Venous blood is removed from the patient's body via a large bore cannula, pumped through an oxygenator and then infused back into the body.
During the H1N1 pandemic in year 2009, some patients developed severe respiratory failure, requiring mechanical ventilation. This is a chest radiograph of one such patient, showing diffuse consolidation of the lungs. A few of these patients have critically low blood oxygen saturation despite potentially toxic levels of oxygen and ventilator pressure.
For example, this patient despite being put on a 100% oxygen and a high inspiratory pressure of 40 cm water, his blood oxygen saturation remained at a dangerous level of 75%. This is when ECMO can be considered as a salvage treatment.
To use ECMO, we first prepare the machine with a primed circuit.
Special ECMO cannulae are then placed into the patient's veins.
Here, we have cannulated the right femoral vein for blood removal. A clamp is applied before blood gushes out of the cannula.
The cap of the cannula is then removed, and the primed circuit is cut open.
The femoral cannula is carefully connected to the circuit. Saline is flushed when making this connection to avoid entrance of air bubbles.
The right internal jugular vein is cannulated for blood return. The connection to the circuit is made carefully again to avoid trapping any bubbles.
After the connections are made, clamps on the circuit are released one by one. Dark deoxygenated blood now can be seen flowing into the circuit and gradually filing up the oxygenator. After coming out of the oxygenator, the bright red oxygenated blood is returned into the patient's body.
Without changing the ventilator setting, the blood oxygen saturation starts to rise. This allows reduction of the oxygen concentration and ventilator pressure to a safe level. The patient will be supported with ECMO until recovery of lung function.
From 1 May 2009 to 28 February 2010, seven patients with confirmed H1N1 infection received ECMO in Hong Kong. One of them died while six made full recovery. You may refer to the article in the Hong Kong Medical Journal for further details.
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