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- Evaluate the adequacy of ventilation, acid–base status, and oxygenation.
- Evaluate the patient’s response to therapy and/or diagnostic evaluation (e.g. oxygen delivery).
- Monitor severity and progression of a known disease process.
Test Before ABG
- The Allen test is a good and valid screening test for the circulation of the hand.
- Absent ulnar circulation – as demonstrated by Modified Allen’s Test.
- Impaired circulation e.g. Raynaud’s Disease
- Arteriovenous fistula
- Distorted anatomy/ trauma/burns to the limb – at or proximal to the
attempted arterial puncture site.
- Severe coagulopathy
- Abnormal or infectious skin processes at/or near the puncture site
- Failure and/or pain
- Haematoma or haemorrhage
- Trauma to the vessel
- Arterial occlusion
- Vasovagal response
- Air or distal clotted-blood emboli
Source of error in blood gas collection and handling
- Sample contaminated with venous blood
- Sample clotted
- Air bubles will falsely elevate the PO2
- Sample contains too much heparin (liquid heparin dilutes the sample, and causes pH changes)
- Haemolysis en route to the ABG analyser
- Inappropriate type of syringe used (gas-tight syringes are needed, rather than evacuated tubes)
- The sample contains an excessive number of leukocytes, and they have consumed all the oxygen (eg. leukaemia blasts)
- The sample took too long to transport, and blood cell metabolism has changed the gas concentration
- Sample was chilled with ice (and then analysed at body temperature values)-Low temperatures also make the ABG syringe polymer more gas-permeable, allowing gases to exchange with the atmosphere.