arterial blood gas (ABG):
is a blood test that is performed by taking blood from an artery, rather than a vein.
It is performed in purpose of analyzing gas exchange process (so that an accurate measurement of oxygen and carbon dioxide levels can be obtained), as well acid-base balance. which then allowing administering patient medication properly
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An ABG is a test that measures the arterial oxygen tension (PaO2), carbon dioxide tension (PaCO2), and acidity (pH). In addition, arterial oxyhemoglobin saturation (SaO2) can be determined.
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Such information is vital when caring for patients with critical illness or respiratory disease. As a result, the ABG is one of the most common tests performed on patients in intensive care units (ICUs).
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Pulse oximetry plus transcutaneous carbon dioxide measurement is an alternative method of obtaining similar information as well.
Invasive Blood vs Noninvasive monitoring.
Indications of arterial access:
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Patients with respiratory disease ,ABG sampling will provide information about lung ventilation through interpretation of the PCO2 and tissue oxygenation through interpretation of the PO2.
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Patients with certain metabolic diseases and selected drug overdoses are at risk for acid-base abnormalities. Acid base problems are diagnosed through interpretation of arterial pH, PCO2 and HCO3 levels.
Indications:
- Respiratory Diseases; ABG provide information on lung ventilation through PCO2, and tissue oxygenation through PO2
- Metabolic Diseases and selected drug overdoses: at risk of acid-base abnormalities, acid base problems are diagnosed through interpretation of arterial pH, PCO2 & HCO3 levels
- Invasive Blood Pressure Monitoring
Contraindications: vascular diseases (Beurger disease), or Inadequate collateral circulation at the puncture site, Coagulopathy, or anti-coagulation therapy, Not performed through lesion (Full thickness burns)
Complications: Hematoma, Thrombus, Infection, Pseudoaneurysm, AV fistula
Arterial Puncture Sites
The wrist radial artery is most common site used
Others include femoral, Dorsalis pedis, brachial.
Alternative sites include:
- Brachial artery at the antecubital fossa .
- Femoral artery just below the inguinal ligament .
- Dorsalis pedis artery in the foot .
Items of ABG - Gather necessary following equipment:
- a blue (22-23 G) needle
- 2ml syringe with heparin
- a cap for the syringe
- a plastic bung
- local anaesthetic (plus needle and syringe for giving)
- alcohol gel
- gauze
- gloves
- a sharps bin
Usually, the syringe, needle, cap and bung are all provided in one pack.
Procedure of ABGZ
- Wash Hands
- Greet patient, explain the procedure, obtain consent, then perform
- Extend wrist
- Locate radial artery with your index and middle finger
- Perform Allen’s test - compress both radial/ulna, ensure good flow
- take cap off, flush heparin through syringe, locate radial with non-dominant hand
- Insert at 30-45 degrees to the skin at the point of maximum pulsation of radial artery - arterial pressure will cause blood to fill syringe
- Remove needle placing into bung
- press firmly to punctured site with gauze for 5 minutes, to halt bleeding
- Remove needle from syringe and discard safely in the sharps bin
- cap syringe, push out any air within it, send immediately for analysis packed in ice.
- Remove gloves, dispose them in waste bin, wash your hands and thank patient
Venous or arterial blood?
Dark, non-pulsatile blood that requires manual suction to aspirate often indicates a venous sample(except in severe shock /cardiac arrest).
Another clue is when Sao2 on ABG analysis is significantly lower than Sao2 on pulse oximetry.
An extension to this station could be Blood gas interpretation - AMBOSS platform
