Arterial Blood Gas Sampling

ABG sampling provides valuable information on the acid-base balance at a specific point in the course of a patient's illness. It is the only reliable determination of ventilation success as evidenced by CO2 content. It constitutes a more precise measure of successful gas exchange and oxygenation. ABG sampling is the only way of accurately determining the alveolar-arterial oxygen gradient (see the A-a Gradient calculator).

Indications

Indications for ABG sampling include the following:

    Identification of respiratory, metabolic, and mixed acid-base disorders, with or without physiologic compensation, by means of pH ([H+]) and CO2 levels (partial pressure of CO2)

    Measurement of the partial pressures of respiratory gases involved in oxygenation and ventilation

    Monitoring of acid-base status, as in patient with diabetic ketoacidosis (DKA) on insulin infusion; ABG and venous blood gas (VBG) could be obtained simultaneously for comparison, with VBG sampling subsequently used for further monitoring
    Assessment of the response to therapeutic interventions such as mechanical ventilation in a patient with respiratory failure
    Determination of arterial respiratory gases during diagnostic evaluations[2, 3] (eg, assessment of the need for home oxygen therapy in patients with advanced chronic pulmonary disease)
    Quantification of oxyhemoglobin, which, combined with measurement of arterial oxygen tension (PaO2), provides useful information about the oxygen-carrying capacity of the patient
    Quantification of the levels of dyshemoglobins (eg, carboxyhemoglobin and methemoglobin)
    Procurement of a blood sample in an acute emergency setting when venous sampling is not feasible (many blood chemistry tests could be performed from an arterial sample[4] )

Contraindications

Absolute contraindications for ABG sampling include the following:

    An abnormal modified Allen test (see below), in which case consideration should be given to attempting puncture at a different site

    Local infection or distorted anatomy at the potential puncture site (eg, from previous surgical interventions, congenital or acquired malformations, or burns)

    The presence of arteriovenous fistulas or vascular grafts, in which case arterial vascular puncture should not be attempted

    Known or suspected severe peripheral vascular disease of the limb involved

Relative contraindications include the following:

    Severe coagulopathy

    Anticoagulation therapy with warfarin, heparin and derivatives, direct thrombin inhibitors, or factor X inhibitors; aspirin is not a contraindication for arterial vascular sampling in most cases

    Use of thrombolytic agents, such as streptokinase or tissue plasminogen activator