How-to Interpret Arterial Blood Gases: Step-by-Step Guide for Nurses & Nursing Students

How-to Interpret Arterial Blood Gases: Step-by-Step Guide for Nurses & Nursing Students

Interpretation of arterial blood gases (ABGs) can be intimidating for any healthcare professional, including nurses. The results of arterial blood gases provide important information about a patient's respiratory and metabolic status. ABGs are usually ordered when a patient has respiratory distress, acidosis, alkalosis or any condition that may affect their oxygenation or ventilation.

ABGs are important because they provide a valuable snapshot of a patient’s pH and oxygenation. A patient’s PaCO2 and PaO2 levels directly influence the levels of oxygen and metabolic processes in the cells. When an ABG reveals an abnormally low or high PaO2, the clinician can diagnose hypoxemia or hyperoxemia, respectively. Likewise, an abnormal pH result can indicate either respiratory or metabolic acid-base disorders. ABGs can also help diagnose acidosis or alkalosis, which can lead to changes in blood pressure, electrolyte balance, and organ function. By closely monitoring a patient’s ABG, clinicians can identify any changes in their acid-base status, oxygenation, and ventilation quickly and accurately.

The goals of interpreting ABGs are to determine:

1. Acidosis or alkalosis

2. Respiratory or metabolic

3. Fully compensated, partially compensated or uncompensated

Interpreting ABGs involves assessing the pH, PaCO2, HCO3-, PaO2, and base excess. Here are some key steps to help you interpret arterial blood gases:

Step 1: Assess pH

The pH of an ABG tells us if the patient is acidotic, alkalotic, or within the normal range. The normal pH range is 7.35-7.45. If the pH is below 7.35, the patient is acidotic, and if it is above 7.45, the patient is alkalotic.

Step 2: Assess PaCO2

PaCO2 measures the partial pressure of carbon dioxide in arterial blood. The normal range is 35-45 mmHg. (*Tip: if you can remember the pH normal range, you can also remember PaCO2 since they both have 35 and 45 in their values!) If the PaCO2 is elevated, it indicates respiratory acidosis. If it is decreased, it indicates respiratory alkalosis.

Step 3: Assess the HCO3-

HCO3- measures the level of bicarbonate ions in arterial blood. The normal range is 22-28 mEq/L. An elevated HCO3- indicates metabolic alkalosis, while a decreased HCO3- indicates metabolic acidosis.

Step 4: Assess the PaO2

PaO2 measures the partial pressure of oxygen in arterial blood. The normal range is 80-100 mmHg. If the PaO2 is under 80mmHg, the patient is considered hypoxic and may require supplemental oxygen.

Step 5: Assess the Base Excess

Base excess measures the amount of excess or lack of alkaline or acid present in the blood. The normal range is -2 to +2 mEq/L. A negative base excess indicates metabolic acidosis while a positive base excess indicates metabolic alkalosis.


It is important to consider all values together to determine if the patient is in respiratory or metabolic acidosis or alkalosis. Nurses must also consider the patient's overall clinical presentation, past medical history, and current condition before making decisions based on ABG results.

In conclusion, interpreting arterial blood gases is an essential skill that all nurses should possess. It provides valuable information regarding a patient's respiratory and metabolic status. Nurses must have a deep understanding of the ABG parameters and their clinical implications to provide the best possible care for their patients.

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