Manual blood samples
Procedures for taking manual blood samples is documented in the quality system in intranet.
Blood samples while "blood pump" 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 blood pump. When samples are collected from the end of the "blood pump" tubing, the time that it takes to collect the sample (TS) and the time that it takes for the blood to traverse through the tubes (TT) may have to be taken into account.
The sample collection should be started TT - TS/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 TS seconds later.
Volume of the tubing
To calculate the time that blood traverses the tubing, the volume of the tubing [ml or cm3] is divided by the blood pump flow rate (usually 6 ml/min, or 0.1 ml/s):
TT = VT / flow rate
The volume can be calculated from the formula VT = (inner diameter [cm] / 2)2 * π * tube length [cm]
When you are writing a new study protocol, always make sure what tubing will be used (ask Tuula Tolvanen).
Allogg (at HR+)
Currently, the tubing of Allogg on-line sampler system consists of two separate tubes. The first has the diameter of 1.6 mm and length 45 cm, and the second 2.2 mm and 45 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 2.68 ml.
If the blood pump flow rate is 0.1 ml/s, then it takes 27 s for the blood to pass through the tubing, and the collection of the blood sample should be delayed this much.
GEMS (at GE Advance)
Ask the researchers of the anaesthesiology group.
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 is 2-2.5 ml. The time that it takes to collect the sample is TS = (sample volume [ml]) / (flow rate [ml/s]). 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.
