A nurse is reviewing an ABG (Arterial Blood Gas) report. If the results are delayed, what may be the most common consequence?

Appeared in: NORCET 7 Prelims -2024

Explanation

After an ABG sample is drawn, blood cells remain metabolically active and continue to consume oxygen.
If analysis is delayed and the sample is not immediately placed on ice, this ongoing oxygen consumption leads to a falsely low partial pressure of oxygen (PaO₂).
This inaccurate oxygenation reading is the most significant and rapid pre-analytical error caused by delayed processing at room temperature.
Guidelines recommend placing the sample in an ice slurry if analysis is delayed beyond 15-30 minutes specifically to slow down cellular metabolism and oxygen consumption.

Option B: ABG syringes are pre-heparinized to prevent blood clotting. Clotting is related to improper sample collection or mixing, not the time delay before analysis.
Option C: While pH does decrease (becomes more acidic) due to the production of CO₂ by metabolizing cells, the change in PaO₂ is considered the more immediate and clinically significant consequence of a delayed sample.
Option D: Cellular metabolism consumes glucose for energy. Therefore, a delay in analysis would cause falsely decreased blood glucose levels, not elevated ones.

Visual 1: Infographic: 'The Life of an ABG Sample.' Shows a syringe at Time 0 with baseline values, and another at Time +30 mins (room temp) with arrows indicating PaO₂ ↓, PaCO₂ ↑, pH ↓, and Glucose ↓.
Visual 2: Flowchart: 'Proper ABG Sample Handling.' Steps: 1. Draw sample in heparinized syringe. 2. Expel air bubbles. 3. Analyze within 15 mins? -> YES: Send to lab. -> NO: Place in ice slurry and transport immediately.

Clinical Relevance

Nursing practice connection: Knowing Pre-analytical errors in Arterial Blood Gas (ABG) sampling helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Accurate ABG results are vital for managing critically ill patients, as decisions about oxygen therapy and mechanical ventilation depend on them.
A falsely low PaO₂ reading could lead a clinician to unnecessarily increase a patient's oxygen supply, which carries risks like oxygen toxicity or absorption atelectasis.
Nurses are responsible for ensuring proper and timely handling of ABG samples to prevent pre-analytical errors and ensure patient safety.

How to Approach the Question

First, identify the core of the question: What happens physiologically in a blood sample after it's drawn from the body?
Recall that blood contains living cells that continue to perform cellular metabolism. This process consumes oxygen and glucose and produces carbon dioxide.
Evaluate each option based on the effects of continued cellular metabolism:
'Inaccurate oxygenation' is plausible because oxygen is consumed.
'Blood clotting' is a separate process prevented by heparin in the syringe, not by timely analysis.
'Incorrect pH' is plausible because CO₂ production makes the blood more acidic.

Concept Tested & Keywords

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Practise the full NORCET 7 Prelims -2024

Attempt every question from this paper in a timed mock, then review the full solution for each one.