Which value can be primarily affected if there is a delay in transferring an arterial blood sample for gas analysis and the sample is not refrigerated?

1. A

   pH

2. B

   pCO₂

3. C

   pO₂

4. D

   HCO₃

Appeared in: NORCERT 8 Mains-2025

Explanation

Listen in Hindi

• When an arterial blood sample is not refrigerated, living blood cells (leukocytes, platelets) continue to metabolize.
• This ongoing cellular metabolism directly consumes oxygen present in the sample.
• The consumption of oxygen leads to a significant and rapid decrease in the partial pressure of oxygen (pO₂).
• This drop in pO₂ is the most direct and immediate consequence of the delay, making it the primarily affected value.

Why Other Options Were Wrong

• Option A: The pH does decrease (becomes more acidic), but this is a secondary effect. It happens because the pCO₂ increases, which then forms carbonic acid.
• Option B: The pCO₂ level increases as cells produce carbon dioxide during metabolism. While this is a direct effect, the consumption of oxygen is the initiating step of aerobic metabolism being measured.
• Option D: Bicarbonate (HCO₃) levels are regulated by the kidneys over a longer period and are not significantly affected by the short-term metabolic changes occurring in a blood sample after collection.

Related Visual

• Visual 1: Infographic: Shows a blood gas syringe at time zero with normal values, and another after 30 minutes at room temperature with arrows indicating pO₂ decrease, pCO₂ increase, and pH decrease.
• Visual 2: Flowchart: Illustrates the process of cellular metabolism in a blood sample: Glucose + O₂ → ATP + CO₂ + H₂O, showing how O₂ is consumed and CO₂ is produced.

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.
• Proper handling of ABG samples is critical for accurate diagnosis and management. A delay can lead to erroneous results, potentially causing incorrect clinical decisions.
• A falsely low pO₂ might prompt a clinician to increase a patient's supplemental oxygen unnecessarily, which can lead to oxygen toxicity, especially in patients with COPD.
• A falsely high pCO₂ and low pH could be misinterpreted as respiratory acidosis, leading to inappropriate changes in ventilator settings.

How to Approach the Question

• First, identify the key elements of the question: an arterial blood sample, a delay in analysis, and no refrigeration.
• Recognize that blood is a living tissue containing cells that are metabolically active.
• Consider the basic process of aerobic cellular respiration: cells consume oxygen (O₂) and produce carbon dioxide (CO₂).
• Evaluate how this process affects the ABG parameters. O₂ consumption will lower pO₂. CO₂ production will raise pCO₂.
• Analyze the secondary effects: an increase in pCO₂ will lead to the formation of carbonic acid, which lowers the pH.
• Determine which effect is 'primary'. The consumption of oxygen is the initial step of the metabolic process in the sample, making the change in pO₂ the most direct and primary consequence.

Concept Tested & Keywords

• Concept Tested: Pre-analytical errors in Arterial Blood Gas (ABG) sampling
• Stem keywords: arterial blood sample, gas analysis, delay in transferring, not refrigerated
• Lead-in keywords: primarily affected

Question ID

QHUGmJFQXYOHbcaUXsbO71

Copy ID