Understanding ABG's

Interpreting an arterial blood gas (ABG) is a crucial skill for physicians, nurses, respiratory therapists, and other health care personnel. ABG interpretation is especially important in critically ill patients. The following six-step process helps ensure a complete interpretation of every ABG. In addition, you will find tables that list commonly encountered acid-base disorders. Many methods exist to guide the interpretation of the ABG. This discussion does not include some methods, such as analysis of base excess or Stewarts strong ion difference. A summary of these techniques can be found in some of the suggested articles. It is unclear whether these alternate methods offer clinically important advantages over the presented approach, which is based on the anion gap.

Why analyse arterial blood gases

As we care for more acutely ill patients with respiratory, cardiac, renal and metabolic disorders, so more of them will have arterial blood gas samples taken. Understanding these results is an essential part of patient care, making patient assessment more informed and patient management more specific. Essentially, arterial blood gases are taken to evaluate the patients: - Oxygenation - Ventilation - Acid base balance. Arterial blood gas analysis requires a clear understanding of the terms used.

Assessing the patients oxygenation

The oxygen partial pressure (PaO2), the measurement of oxygen dissolved in the blood, is an important indicator of potential tissue oxygenation. The normal value is between eight and 12 kilopascals (kPa). Hypoxaemia, or a low PaO2, deprives cells of oxygen and leads to irreversible cell damage. It can result from hypoventilation, airway obstruction and atelectasis. Older patients and those with chronic respiratory disease tend to have lower oxygen levels. It is therefore important to establish the acceptable PaO2 for each patient to administer appropriate oxygen therapy. The oxygen saturation, SaO2, is the percentage of saturated haemoglobin carrying oxygen compared with the total amount of oxygen it could carry. An SaO2 of more than 95% is normal for a healthy adult and can be determined by ABG analysis or by pulse oximetry.