Blood sampling while ABSS is running

During on-line blood activity measurement the discrete blood samples should be collected from the end of the blood tubing to prevent interfering with the ABSS. When samples are collected from the end of the ABSS tubing, the time that it takes to collect the sample (T_S) and the time that it takes for the blood to traverse through the tubes (T_T) may have to be taken into account.

The sample collection should be started T_T - T_S/2 seconds later than the "official" sample time is. Note that the sample must still be polled at the "official" sample time. The required sample volume is collected T_S seconds later.

Volume of the tubing

To calculate the time that blood traverses the tubing, the volume of the tubing (V_T, in ml or cm³) is divided by the blood pump flow rate (F, usually 6 ml/min, or 0.1 ml/s):

$T_T = \frac{V_T}{F}$

The volume can be calculated using inner diameter of the tube (D, in cm), tube length (L, in cm)

$V_T = {(\frac{D}{2})}^2 \times \pi \times L$

When you are writing a new study protocol, always make sure what tubing will be used (ask Tuula Tolvanen).

Allogg

Currently (2010-06-23 TT), the tubing of Allogg on-line sampler system consists of two separate tubes. The first has the diameter of 1.5 mm and length 45 cm, and the second 2.05 mm and 40 cm, accordingly. The tubing also contains connectors etc, the volume of which may be estimated as 0.06 cm³. Thus, with this tubing, the total blood volume inside it is about 2.18 ml.

If the blood pump flow rate is 0.1 ml/s (6 ml/min), then it takes 22 s for the blood to pass through the tubing, and the collection of the blood sample should be delayed this much.

Volume of the blood sample

It is preferred to start the collection of the blood sample before the sample time so that half of the sample is collected at the sample time, and the other half of the sample will be collected after it.

In most cases, the volume of the blood sample (V_S) is 2-2.5 ml. The time that it takes to collect the sample is

$T_S = \frac{V_S}{F}$

Thus, if the sample volume is 2 ml, and the blood pump flow rate is 0.1 ml/s, the collection of the sample takes 20 s. In this case, the sample collection should therefore be started 10 s before the sample time.

Blood sampling while ABSS is running

Volume of the tubing

Allogg

Volume of the blood sample

See also: