- Clinical science
Arterial blood gas (ABG) analysis is a test regularly performed to measure oxygen saturation, carbon dioxide, and bicarbonate blood levels. It provides quick assessment of gas exchange processes and acid-base balance. Pulse oximetry is a non-invasive and quick way of measuring the oxygen saturation of peripheral arterial hemoglobin. The test relies on the fact that oxygenated and deoxygenated hemoglobin absorb different wavelengths of light. Physiological levels of oxygen saturation are generally above 95%.These tests provide vital information about a patient that is especially important in emergency and intensive care settings.
- Partial pressure of oxygen in arterial blood (PaO2); and partial pressure of carbon dioxide (PaCO2) in arterial blood
- Base excess: Excess value of base in the blood. Used to identify whether an acid-base imbalance is predominantly a respiratory, metabolic, or a mixed acid-base disorder.
- Standard bicarbonate
- Modern blood gas analyzers also measure: some electrolytes (i.e., sodium, potassium, chloride, calcium), blood glucose, hemoglobin, methemoglobin and carboxyhemoglobin concentrations
- Reference ranges
A modified Allen test must be performed before the radial artery is punctured to assess collateral circulation in the hand.
- Manual pressure below the wrist is applied to both arteries, the hand is elevated, and the patient is asked to clench their fist for about 30 seconds to induce transient ischemia, leading to pallor of the hand.
- When the pressure is released from the ulnar artery, the patient's hand rapidly returns to normal color if collateral circulation is present.
- Interpretation: The test result is normal if the patient's hand rapidly returns to normal color. The test is negative and considered pathological if the patient's hand remains at least partially pale.
- Arterial blood can be drawn from radial arteries or an indwelling arterial catheter.
- A modified Allen test must be performed before the radial artery is punctured to assess collateral circulation in the hand.
- Reference range: 65–70%
- Increased tissue oxygen extraction due to decreased oxygen delivery to tissue
- Increased oxygen consumption by tissues
- Inability of hemoglobin to bind to oxygen (e.g., carbon monoxide poisoning)
- Increased SvO2
- Decreased SvO2