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

When ABG analysis is delayed, living blood cells continue their metabolic processes.
The most direct and significant metabolic process affecting the results is the consumption of oxygen by these cells.
This cellular respiration leads to a falsely low partial pressure of oxygen (PaO2) reading, resulting in inaccurate oxygenation results.
While other parameters like pH and PaCO2 also change, the drop in PaO2 is the most immediate and pronounced consequence.
To prevent this, samples must be analyzed immediately or placed on ice to slow cellular metabolism.

Option B: Blood clotting is prevented by the use of an anticoagulant, typically heparin, in the collection syringe. A delay in analysis does not cause clotting.
Option C: While pH levels do become incorrectly acidic due to the production of CO2 by metabolizing cells, the primary metabolic event is the consumption of O2. The change in PaO2 is more direct and often considered the most significant error.
Option D: Living cells in the blood sample consume glucose for energy (glycolysis). Therefore, a delay in analysis would lead to falsely decreased blood glucose levels, not elevated ones.

Clinical Relevance

Nursing practice connection: Knowing Pre-analytical variables 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 critical for managing critically ill patients, guiding ventilator settings, and assessing acid-base emergencies.
A falsely low PaO2 could lead to inappropriately increasing a patient's oxygen therapy or even unnecessary intubation, exposing the patient to risk.
Nurses are often responsible for collecting and transporting ABG samples. Understanding the importance of immediate analysis or proper storage (icing) is a key patient safety competency.

How to Approach the Question

First, identify the core of the question: What happens to a 'living' blood sample over time?
Recall the basic principles of cellular metabolism: cells use oxygen and glucose to produce energy, releasing carbon dioxide as a waste product.
Apply this principle to the ABG parameters. Oxygen (PaO2) will be consumed, so it will decrease. Carbon dioxide (PaCO2) will be produced, so it will increase. An increase in CO2 (an acid) will cause pH to decrease.
Evaluate the options based on this understanding.
Option A (Inaccurate oxygenation): This matches the principle that O2 is consumed.
Option C (Incorrect pH): This also matches, but it's a secondary effect of CO2 production.

Concept Tested & Keywords

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E6 Pathology-Vandana Puri & Kavita Gaur Textbook of Pathology and Genetics p. 407-409

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart B (pp 240-463 of 478) p. 82-84

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.