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Arterial blood gas (ABG) testing is an essential tool in managing critically ill patients and people with respiratory disease. ABGs measure concentrations of oxygen and carbon dioxide in arterial blood, providing information about respiratory function. At the same time, by measuring pH and associated parameters, ABGs can provide evidence of acid-base disturbances and metabolic imbalance.
To interpret ABG results, nurses must understand the underly- ing physiological processes determining gas concentrations and pH regulation, and the way these are altered in disease. Use of a systematic approach when reading ABG results allows deter- mination of hypoxaemia, hypercapnia, metabolic or respiratory acidosis and alkalosis, and whether these are uncompensated or compensated states.
Introduction
Arterial blood gas (ABG) analysis is an essential component in managing critically ill patients, those in respiratory failure, and patients with chronic respiratory conditions. In the community, ABG analysis is used to determine if a person is eligible for funded domiciliary oxygen therapy. ABG analysis provides information about the oxygen and carbon dioxide concentrations in arterial blood and, therefore, important in- formation about lung function in the presence of respiratory conditions. Also, ABG testing determines the acid-base balance in the body, the source of any imbalance and a patient's ability to compensate for disturbance in pH.
The increasing availability of pulse oximetry has, to some extent, reduced the need for ABG testing, but pulse oximetry is not a substitute for ABG. The pulse oximeter can only pro- vide information about a patient's oxygen status. It does not measure carbon dioxide, pH or bicarbonate concentration, and cannot be relied on to detect respiratory failure.
ABG analysis provides measurements for an array of parameters, so it can be confusing knowing where to start interpreting them. The use of ABGs in acutely ill or deteriorat- ing patients requires rapid and accurate interpretation: test results often determine immediate changes in therapy and outcomes.
Sampling ABGs
ABG samples are generally obtained from the radial artery via puncture, or from an arterial catheter, using a syringe primed with dry heparin. The radial artery is the most common choice for arterial puncture because it is easy to get at and can be compressed against the wrist liga- ments afterwards to reduce haematoma. Arterial blood is highly sensitive to errors in...