Pre sample blood volume

[Guest Salma]

Hi all

How much is the pre sample volume of blood should be withdrawn from UAC or PAL ?

Should the pre-sample be returned back? What is the technique to be used?

Can you plz share the practice in your unit?

any evidence or link ?

Regards

[salameh101]

A-SALAMO ALAYKOM-the pre sample volume of blood should be withdrawn from UAC or PAL depend on the size of the baby,700 gram dif- from 2-3 kg baby,2-3 ml is good to flash the catheter,shoud be heparinized , under complet aseptic technique and rapid to prevent clot formation ,air should be removed,all planed sample should be at the same time,3 ways conection to be used.

[Stefan Johansson]

Hi!

One should always try to minimize pre sample blood withdrawal, since hemodynamics change during blood withdrawal.

http://www.ncbi.nlm.nih.gov/pubmed/17937686

http://www.ncbi.nlm.nih.gov/pubmed/16373299

Pace of withdrawal seems to matter too: http://www.ncbi.nlm.nih.gov/pubmed/12509598

For the smallest infants with 2.5G UAC we typically withdraw <1 ml.

[Francesco Cardona]

Interestingly the two paper you quoted come to different conclusions: Claudia Roll et al recommend drawing less blood to minimize drop in cerebral oxygenation while Schulz et al believe it is just a matter of time - 40s being adequate to keep cerebral oxygenation stable. Level of prematurity might be the difference as median gestational age was lower in Roll's study (27wks) compared to Schulz (30wks).

[Stefan Johansson]

Interestingly the two paper you quoted come to different conclusions: Claudia Roll et al recommend drawing less blood to minimize drop in cerebral oxygenation while Schulz et al believe it is just a matter of time - 40s being adequate to keep cerebral oxygenation stable. Level of prematurity might be the difference as median gestational age was lower in Roll's study (27wks) compared to Schulz (30wks).

One major difference between these two studies is that blood withdrawal from umbilical vein and umbilical artery catheters were studies, respectively. I think the point is rather that sampling may matter (volume and/or time). For a tiny premiee drawing 2 ml of blood may correspond to several % of the total blood volume.

[Francesco Cardona]

One major difference between these two studies is that blood withdrawal from umbilical vein and umbilical artery catheters were studies, respectively. I think the point is rather that sampling may matter (volume and/or time). For a tiny premiee drawing 2 ml of blood may correspond to several % of the total blood volume.

I am afraid I cant follow you. What do you mean by saying that the two studies were studies? My idea was that these studies tried to find the best way to sample blood from umbilical artery catheters. I presume that in general we might try to keep loss through sampling to a minimum. On the other hand you might find inaccuracies if you draw not enough blood as well. I wonder if you could trust values if you only draw 0.2ml through an UAC as suggested in the study by Roll et al.

[Stefan Johansson]

Hoppla! Typo! I meant that the two studies investigated blood withdrawal from UAC and UVC respectively. One may think that presampling from the venous return may have less impact on hemodynamics than sampling from aorta.

We typically withdraw 0.5 ml from the smallest UAC.

I think this could be a topic for a nice experimental study: design/build experimental blood vessels/a vascular tree, flow blood through it, apply a catheter with drip and then pre-sample blood in various volumes to see how much volume is needed to withdraw for, for example, reliable electrolytes. Piece of cake!

[Guest JoannieO]

Hi there,

In our unit it is the practice to draw 0.9 - 1.0ml from the UAC or PAL prior to sampling. This is returned after the sample has been taken. We do not draw blood from UVCs unless it is at the time of insertion.

I will be interested to see what the practice is in other units.

Regards to all

[kpsanghvi]

We usually withdraw 1 ml from an arterial line and return it after the sampling. Sampling is done from the UVC only if there is no arterial line available in which case we are a little more generous and would withdraw 1.5ml. But all presampling aspirates are returned followed by a flush of 0.5ml to 1ml of NS

[Guest sageaugie]

Hi,

Wish to restart a old thread. Is UVC sample ( not at the time of insertion) reliable for a platelet count and electrolytes?