1. Arterial blood gas (ABG) analysis requires a sample of arterial blood for measurement of pH, partial arterial carbon dioxide pressure (PaCO₂), partial arterial oxygen pressure (PaO₂), bicarbonate (HCO₃^–), and percent oxyhemoglobin saturation (SaO₂) to assess a patient’s respiratory, metabolic, and acid-base status.

2. Given the shape of the oxyhemoglobin dissociation curve, oximetry alone for SaO₂ measurement may not be reliable because there must be a substantial fall in PaO₂ before oximetric SaO₂ is appreciably altered. However, the SaO₂ determined by pulse oximetry may be more accurate than calculated SaO₂ from the ABG because the latter value cannot be corrected for variables such as the binding characteristics of hemoglobin (Hb) and 2,3-diphosphoglycerate.

3. The HCO₃^– in an ABG is calculated in contrast to the HCO₃^– measured in venous chemistries.

1. A glass syringe is the standard to which all other methods are compared. If a large enough needle is used, entry is apparent because the syringe fills by the pressurized arterial flow of blood, without the need for applying a vacuum or using a vacuum-sealed collecting tube.

2. Other plastic ABG kits are available that have directions specific for the type of collection syringe offered (see Section IV.A).

1. Using correction values, a venous blood gas (VBG) is useful when oxygenation is not suspect (i.e., past ABGs have correlated well enough with oximetric saturations, and there is no suspicion of a substantial change in oxygenation) and the patient is hemodynamically stable.

2. Arterial catheterization is an option if frequent ABG measurements are needed (see Section V.A).

1. Abnormal acid-base and blood oxygenation can quickly lead to unresponsiveness, serious cardiac arrhythmias, and death and can alert
the physician to reversible causes of tissue hypoperfusion, metabolic derangements, and respiratory arrest.

2. An ABG should be obtained when there is undiagnosed altered mental status, abnormal breathing pattern, suspicion regarding the accuracy of hypoxemia by oximetric saturations, or abnormal HCO₃^– on chemistry laboratory tests.

3. Discrepancy between SaO₂ by pulse oximetry and that calculated by the ABG can aid in the diagnosis of carboxyhemoglobinemia and methemoglobinemia.

4. Values from an ABG allow determination of arterial content of oxygen (CaO₂), oxygen delivery (DO₂), oxygen consumption ([V with dot above]O₂), and alveolar-arterial PO₂ (A-a) gradient.

A. Puncturing a surgically reconstructed artery may

1. Result in a pseudoaneurysm

2. Compromise the integrity of the graft site

3. Seed the foreign body, rendering it a nidus for infection

B. Severe peripheral vascular disease

1. Diminished or absent peripheral pulses distal to a brachial or femoral puncture

2. Poor collateral circulation

C. Local infection