ABGs

Arterial blood gas analysis (ABG) is a laboratory test that measures the amounts of oxygen and carbon dioxide in arterial blood and assesses the acid-base balance of the body. It is commonly used to evaluate respiratory function, ventilation, and metabolic status, particularly in acutely ill or critically ill patients.

The test reports several values, including pH, partial pressure of carbon dioxide (PaCO2), partial pressure of oxygen (PaO2), bicarbonate concentration (HCO3-), and base excess. In many laboratories, oxygen saturation (SaO2) and, when indicated, lactate levels are also reported. The pH indicates overall acidity or alkalinity; PaCO2 reflects ventilation, and HCO3- reflects metabolic compensation. PaO2 assesses oxygenation. Normal ranges at sea level roughly are pH 7.35–7.45, PaCO2 35–45 mmHg, PaO2 75–100 mmHg, HCO3- 22–26 mEq/L, and base excess about -2 to +2 mEq/L; lactate is typically less than 2 mmol/L.

Indications for ABG include evaluation of suspected acid-base disorders, assessment of respiratory failure or metabolic disturbances, management of ventilated patients, and monitoring oxygenation and therapy in conditions such as COPD, sepsis, shock, or postoperative care. Interpretation integrates the pH, acid-base components, and clinical context to classify disorders as metabolic or respiratory and to assess the degree of compensation.

Procedure and handling involve drawing an arterial blood sample, typically from the radial artery, though other sites may be used. The sample must be collected in a heparinized syringe, kept at room temperature or cooled if delay is anticipated, and analyzed promptly to avoid gas changes. Risks are related to arterial puncture, including bleeding, hematoma, arterial injury, and infection. ABG results should be interpreted alongside other clinical information and may differ from venous blood gas values.