In ABG analysis, which parameters are assessed?

Appeared in: RUHS, Jaipur, M.Sc Nursing Entrance Exam-2018

Explanation

A complete Arterial Blood Gas (ABG) analysis evaluates both the body's acid-base balance and its oxygenation status.
To do this, it must measure four key parameters: pH (overall acidity/alkalinity), PaCO2 (the respiratory component), HCO3− (the metabolic component, i.e., sodium bicarbonate), and PaO2 (oxygen level).
This option is the only one that includes all four essential components required for a comprehensive assessment.

Option A: This option is incomplete. It only includes the metabolic component (bicarbonate) and the overall pH, but omits the respiratory (carbon dioxide) and oxygenation (oxygen) parameters.
Option C: This option is incomplete because it omits the partial pressure of oxygen (PaO2). Assessing oxygenation is a primary goal of ABG analysis, especially in patients with respiratory distress.
Option D: This option is incomplete as it omits the bicarbonate (HCO3−) level. Bicarbonate is the primary metabolic parameter, and without it, it's impossible to determine if an acid-base imbalance has a metabolic cause.

Clinical Relevance

Nursing practice connection: This is primarily an exam-oriented knowledge point with limited direct bedside application, so retain Parameters of Arterial Blood Gas (ABG) Analysis as background academic context rather than a clinical decision trigger.
ABG analysis is fundamental in critical care settings to diagnose and manage life-threatening acid-base imbalances (like acidosis or alkalosis) and respiratory failure.
Before drawing an ABG sample from the radial artery, a nurse must perform the Allen's test to confirm adequate collateral circulation to the hand, preventing ischemic injury if the radial artery is damaged.
What if? If a patient has COPD, their baseline PaCO2 might be chronically elevated (e.g., 55 mmHg). In this case, the nurse would look for acute changes from the patient's baseline rather than just comparing to the standard normal range.

How to Approach the Question

First, identify that the question asks for the components of an Arterial Blood Gas (ABG) analysis.
Recall the primary purpose of an ABG test: to assess both acid-base balance and oxygenation status.
Remember the four key parameters needed for this full assessment: pH (overall balance), PaCO2 (respiratory component), HCO3− (metabolic component), and PaO2 (oxygenation).
Systematically review each option to find the one that includes all four of these essential components.
Eliminate options that are missing one or more key parameters.

Concept Tested & Keywords

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E6 Nursing Fundamentals Taylor p. 785-787

E6 textbook of Applied Biochemistry and Nutrition & DieteticsHarbans Lal (pp 26-464 of 479) p. 155-157

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