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Archive for the ‘Blood gas analysers and analysis’ Category

Blood gas analysis and analysers.

These are something you may or may not come across.

You may be asked to look after them. If you are you do need to be trained.

First to say you should always wear gloves and possibly a paper mask when you handle blood in syringes or in capillaries tubes and when doing jobs like emptying the waste bottle.

Blood gas analysers are quite specialised bits of analytical equipment that are expensive to buy and very expensive to run, they also need day to day maintenance by someone who knows what they are doing if they are not maintained they will fail inside a few days, also without a good and reliable supply of spares of one sort or another they will also fail.

They will also need a good stabilised electricity supply.

A very basic one will measure blood pH, carbon dioxide and oxygen. More complicated ones will measure blood pH, carbon dioxide, oxygen, sodium, potassium, calcium, chloride, glucose, lactate, creatinine, bilirubin and haemoglobin. There are analysers that will measure even more parameters but you are unlikely to come across them, I never did. From the measured parameters, it is able to calculate a number of other parameters.

They need a good supply of heparinised syringes and capillary tubes (if you are doing babies) for collecting the blood in. They need solutions, rinse, calibrating and de-protinising solutions and printer paper. In an ideal world, they need to have at least three levels of quality controls daily but some people are happy to do only one per day, Level 1 then next day level 2 and the following day level 3. They also need expensive spares.

All in all they are really only suitable for large reasonably well-funded hospitals.

I don’t propose to write about looking after them other than a few general notes, largely because there are a number of different makes and many different models and they are all slightly different although the general principles are similar.

However, there are a few things that are common practice to all of them.

Every day they must have a number of quality controls done to check that they are capable of giving accurate results. If the machine does not store the results in its computer, keep a notebook besides the machine to record the results in.

They must have their levels of rinse and calibrating solutions checked every day to ensure they will work correctly.

They need to be kept clean and the waste blood safely disposed of.

In use they will suck in or have injected in a small quantity of blood from a syringe or a capillary tube. These syringes or capillary tubes must be heparinised to prevent the blood clotting. Years ago you added your own heparin but these days they come pre-heparinised.

Inside there are very small pathways that the blood travels through to get to the electrodes that do the measuring; these can clot up very easily if not treated properly.

On modern machines, there is a pump to suck the blood in and to flush it away after analysis.

That is as much as I want to write about their workings and maintenance.

With newer machines, you can set them up to require a pass number to use them. The idea is to prevent people using them who have not been trained.

With that in mind, you should set up a training program to train those who are likely to need to use them. Once trained you issue them with a pass number. They must NOT share their number with anyone who is not trained.


What I will write about is the way that the samples should be handled because you may be asked to analyse blood if you are also looking after the machines, correct handling is vital to getting accurate results and to prevent the machine being damaged.

The results from any analysis will only reflect the bloods status at the moment of sampling, and while this is not your problem as a technician, the medical people should record the results along with the respiratory status of the patient at the time of sampling, ventilator settings, pO2 and respiratory rate if the patient is ventilated or simply that they are breathing unassisted with or without added oxygen.

From my own experience the two main makers are Radiometer and Ciba Corning both make excellent machines.

Samples are collected in either a syringe for adults and larger children but in capillary tubes for small and neonatal children. They are normally arterial samples.

Both of them should contain dry electrolyte balanced heparin. This will prevent the blood clotting and by balancing for electrolytes to prevent errors in the electrolyte results. These days they come with the heparin already in them. Liquid heparin, that years ago you added your self, dilutes the sample and causes errors that decrease the true values, often by more than 10%.

Before you start the syringe should have a sticky label on it to identify the patient from which the sample was taken.

Once the sample has been taken from the patient any air bubbles in it should be expelled by holding the syringe vertically and tapping the syringe with your fingernail allow the bubble to rise to the tip, with a piece of gauze or cotton wool over the tip to prevent blood spillage the plunger is gently pressed in to expel the air, immediately after that a cap should be put on to prevent contamination with room air or a clot forming at the tip.

The syringe should then be rolled between the fingers and from end to end to make sure that the sample is properly mixed with the heparin and prevent what are called micro clots, these can damage the analyser and/or bias the results.

It should then be taken to the analyser straight away and analysed. With even a short delay you should expel the first few drops into a piece of gauze as these may have started to coagulate.

Some times there can be a delay between taking the sample and the moment of analysis.

The problem here is that as the blood is a living thing it continues to metabolise also there can be a small amount of gas diffusion through the sides of the plastic syringe, though I would say this was minimal, lastly there can be potassium leakage from the red blood cells if they get damaged.

If it is to be stored for more than ten minutes, it should be cooled down to somewhere between 0C and 4C to slow down the metabolism by putting it in a refrigerator or in a container of water with a few ice cubes in it. Do not freeze it.

It should not be stored cooled for more than thirty minutes.

If it has been stored for up to thirty minutes it may have separated out so it is important to mix it properly before analysing it.

Capillary samples.

These are more difficult to get blood with and require some skill, though this will not be your problem. The capillary tube should be completely filled with no bubbles in it when you get it. Capillary sample results may be significantly different from arterial samples, depending on peripheral circulation.

Both ends of the capillary tube should have a cap on.

Sometimes the sample will have a couple of small bubbles in it. Some makers recommend using what is called a ‘Flea’ a small piece of metal rod that is put into the tube

After sampling, a small magnet is used to drag the ‘Flea’ up and down the tube to mix the blood with the heparin and to cause any air bubbles to go to one end.

When the analysis is complete the syringe or capillary tube should be properly disposed of in a sharps bin.

The results should come out on a ticket printer and be stored in the memory of the machine.

When the results come out write on the printed results the patients name and take it to the person who gave you the blood. Modern machines allow you to enter various details into the computer before you start the analysis, these will be printed on the results print out.

At the interval recommended by the makers, deproteinising solution should be put in. It is a solution of bleach and will clean the blood pathways of proteins that will, if left, risk causing the machine to clot up.

All analysers will come with an extensive users manual, if you do not get one or it has been lost contact the firm for a new one. They may be downloadable from the internet, but do not expect it.

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