Requirements for a reliable ABG sample
An arterial blood gas result is only as good as the sample. A reliable sample is free of air, capped, labeled with the oxygen delivery, mixed by gentle rolling, and analyzed promptly. For plastic syringes kept at room temperature, this unit requires analysis within 30 minutes of the draw. Sample P meets every requirement: air expelled, rolled gently, kept at room temperature, and analyzed at 25 minutes.
How each handling error distorts the result
Each of the other samples fails one requirement, and each error changes the values in a predictable way.
| Sample | Handling | Problem |
|---|
| P | No air, rolled gently, room temperature, 25 min | Correct; result can be relied on |
| Q | No air, rolled gently, iced, 50 min | Exceeds the 30-minute limit; icing does not rescue a plastic syringe held too long |
| R | Small bubble left, rolled gently, 5 min | Air equilibrates with the blood; values shift toward room air |
| S | No air, shaken hard, 10 min | Vigorous shaking can hemolyze the sample |
Why air and delay matter
Watch out! Even a small air bubble matters. Room air has a much higher oxygen and much lower carbon dioxide tension than the blood of most clients, so gas moves between the bubble and the blood: the PaO2 is pushed toward the room-air value and the PaCO2 falls. Fast analysis does not correct this, because equilibration begins at once. With delay, blood cells keep metabolizing, consuming oxygen and producing carbon dioxide and acid, so PaO2 and pH fall and PaCO2 rises. Plastic is slightly permeable to gases, and chilling a plastic syringe does not reliably prevent these changes; ice is used only when the laboratory specifically requires it.
Why mixing must be gentle
The heparin in the syringe must be mixed with the blood to prevent clotting, which is done by rolling the syringe between the palms and gently inverting it. Shaking it hard damages red cells (hemolysis), which can falsely raise potassium and interfere with other measurements on the analyzer. A clotted sample is equally unreliable and may block the machine.
Other essentials
The label records the client's oxygen setting (here 4 L/min by nasal cannula), because PaO2 cannot be interpreted without it, and the client's temperature if required. Before arterial puncture of the radial artery, collateral circulation is checked, and afterward firm pressure is held at the site for at least 5 minutes, longer if the client is anticoagulated. This client receives intermittent hemodialysis, which often involves heparin, so the site is watched for bleeding.
Exam takeaway
Key point! A reliable ABG: no air, capped, labeled with oxygen delivery, gently rolled, and analyzed within the time limit. Icing does not fix a delay, quick analysis does not fix a bubble, and shaking causes hemolysis.