Blood simple
BMJ 2005; 330 doi: https://doi.org/10.1136/sbmj.0506234 (Published 01 June 2005) Cite this as: BMJ 2005;330:0506234
- Peter Cartledge, preregistration house officer1,
- Georgina Moore, preregistration house officer1
- 1St James's University Hospital, Leeds
After years of hard grind at medical school, and armed with all that knowledge, you are ready to start saving lives. Then, suddenly you are brought back to earth with a bump when you realise that most of your first year will be spent filling in forms and taking blood. Soon enough the dreaded first night comes around. The time is 3 am, and you are struggling to take blood from a patient who needs an urgent cross match for a blood transfusion. You run through the options in your mind. Should you call a more senior doctor, or should you try again in the blind hope that you will hit the vein? Before you start to panic, try some of these helpful tips on taking blood and doing peripheral cannulation.
Myths about venepuncture
You cannot take blood from a cannula once it has been used
This is false. A number of studies have now shown that there is no significant difference between the laboratory values of samples taken from a peripheral cannula and those taken by venepuncture.1–3 But remember, the bigger the cannula, the easier it is to take blood. You should not use a cannula smaller than 20 gauge. However, you cannot take a clotting sample from a cannula if it has been flushed with heparinised saline or if a heparin infusion has been going through it.4
You cannot take blood from an arm with an infusion running
Again, this is false. You can take blood anywhere distal to the cannula or just stop the infusion for two to three minutes then use the cannula or new proximal insertion site.5
You should not insert a cannula into the feet
This is false too. But you should only do it if absolutely necessary. Cannulation …
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