icuECMO: Daily Care: Laboratory Values

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Daily Care: Laboratory Values:

Management of the ECMO patient requires frequent laboratory investigations. At minimum the following should be measured daily:

The centrifugal pump will tend to hemolyze the patient's red blood cells.
A gradual decline in hemoglobin will be seen as patients remain on ECMO.
At TGH, transfusion of red blood cells is considered for a hemoglobin less than 80 mg/dl.
A precipitous drop in hemoglobin should not be attributed to hemolysis, and should prompt the team to investigate for bleeding.

ECMO therapy will result in the consumption of the patient's platelets via deposits of fibrin on the oxygenator.
In the absence of active haemorrhage, the threshold for platelet transfusion is 50,000.

In general, the pH should be kept between 7.35 and 7.45.
If there is a respiratory alkalosis or acidosis, the sweep can be adjusted to correct the pH.
Metabolically driven alterations in pH should be investigated.

In V-V ECMO, the pO2 is determined by the delivery of blood and oxygen to the membrane oxygenator.
The pO2 should be kept high enough to deliver oxygen adequately to tissues.
A problem with pO2 is one of two things:

The cause of a low pO2 must be investigated (see troubleshooting section for more details), but the delivery of oxygen can be increased by:

In V-A ECMO, there is mixing of blood from the oxygenator and blood that passes through the patient's heart and lungs.
The pO2 is usually measured from the patient's right radial artery.
If the patient has poor pulmonary function, then well-oxygenated blood from the oxygenator will mix with poorly-oxygenated blood from the patient's native pulmonary circulation and result in hypoxemia.
Low pO2 can be corrected by increasing the flow thereby decreasing the relative proportion of blood going through the patient's pulmonary vasculature.
Low pO2 can also be corrected by increasing the FiO2 of the sweep gas, but the cause must be investigated (see troubleshooting section for more details).

To assess the function of the membrane oxygenator, a comparison of the pre- and post membrane gases can be made.
The pre-membrane gas is drawn by the perfusionist from a port just before the blood reaches the oxygenator, typically the pO2 is 40-70 mmHg.
The post-membrane gas is drawn by the perfusionist from a port just after the blood leaves the oxygenator, typically the pO2 is 300-500.
There pO2 should be much higher in the post-membrane gas compared to the pre-membrane gas.
If the increase in pO2 is lower than expected, then this implies there is a problem with the membrane.
In V-V ECMO, if the pre-membrane pO2 is much higher than expected, then this implies there is a "recirculation": the drainage cannula is drawing back oxygenated blood directly from the return cannula instead of allowing that blood to perfuse the patient's organs (see troubleshooting section for more details).