Arterial Blood Gas Chart: Essential Guide to Understanding Key Values

The arterial blood gas (ABG) test is a critical tool in assessing respiratory and metabolic function. It measures oxygen and carbon dioxide levels, pH balance, and electrolyte concentrations in arterial blood. This chart breaks down the main components of an ABG result, helping clinicians interpret whether a patient’s blood chemistry falls within normal ranges or indicates imbalance.

What Is an Arterial Blood Gas Test?

An ABG test involves drawing blood from an artery—commonly the radial, brachial, or femoral artery—using a needle. The sample reveals vital information about gas exchange, acid-base status, and organ function. It is routinely used in emergency medicine, intensive care, and pulmonology to guide treatment decisions.

Primary Values on the ABG Chart

The central values displayed in the ABG chart include:

• pH: Measures acidity or alkalinity. Normal range is 7.35–7.45. Values below 7.35 indicate acidosis; above 7.45 signal alkalosis.
• PaO2: Partial pressure of oxygen, reflecting lung oxygenation. Normal range is 75–100 mmHg at sea level. Values below 60 mmHg suggest hypoxemia.
• PaCO2: Partial pressure of carbon dioxide, indicating respiratory function. Normal range 35–45 mmHg. Elevated PaCO2 signals respiratory acidosis; decreased levels indicate respiratory alkalosis.
• HCO3⁻ (Bicarbonate): Metabolic component, normal range 22–26 mEq/L. Helps assess metabolic contributions to acid-base balance.
• SaO2 (Arterial Oxygen Saturation): Percentage of hemoglobin saturated with oxygen, normal 95–100%. Low SaO2 indicates impaired oxygen delivery.

Interpreting the ABG Chart: Step-by-Step

Proper interpretation begins with the pH to determine acid-base status. Next, evaluate PaO2 and PaCO2 to identify respiratory causes. Then assess bicarbonate to detect metabolic components. For example:

• If pH drops and PaCO2 rises, respiratory acidosis is likely.
• If pH is low and HCO3⁻ drops, metabolic acidosis is present.
• A normal pH but abnormal PaO2 suggests oxygenation issues unrelated to CO2.

Combining these values allows clinicians to pinpoint causes—such as COPD exacerbations, pneumonia, or acute respiratory distress syndrome—and tailor treatments like ventilation adjustments or fluid management.

Supporting Concepts & Clinical Relevance

Beyond core values, the ABG chart may include other markers like base excess, anion gap, and electrolyte levels (sodium, potassium). These provide deeper insight into tissue perfusion, tissue hypoxia, and organ stress. Recent guidelines emphasize integrating ABG results with clinical findings and patient history to avoid over-reliance on single values.

Visual Reference: The ABG Chart Layout

The ABG report typically features columns: pH, PaO2, PaCO2, HCO3⁻, SaO2, and sometimes base excess. Normal ranges are clearly marked, enabling quick comparison. Some labs use color coding—green for normal, yellow for mild, red for severe deviations—to enhance readability.

Conclusion: Take Action with ABG Knowledge

Understanding the arterial blood gas chart empowers healthcare providers and students to make faster, more accurate clinical decisions. Whether managing critical care patients or studying physiology, mastering ABG interpretation supports better patient outcomes. Use this chart routinely, cross-reference with symptoms, and stay updated with evolving clinical standards. Start applying this knowledge today—accurate ABG analysis saves lives.