Effect of variation in haematocrit.
In this experiment, the effect of varying haematocrit on PaO2 in a patient on VV ECMO has been examined.
The data shown above are from a simulated patient with severe respiratory failure and an oxygen consumption of ~200 ml/min on VV ECMO at a pump flow rate of 4.8 lpm. The haematocrit has been varied between 25 and 40 %. The achieved PaO2 (after a stabilisation period of 15 minutes) at four different haematocrits is shown.
As can be seen, there is a progressive rise in achieved PaO2 as haematocrit is increased.
This simple experiment illustrates another important concept of VV ECMO – that, in addition to blood flow through the device, the oxygen-carrying capacity of the blood is an important determinant of oxygenating efficiency.