ABSTRACT
An arterial blood gas (ABG) analyser primarily measures the hydrogen ion concentration (pH) and blood gas tension or partial pressure of oxygen (PaO2) and carbon dioxide (PaCO2) dissolved in the blood and then calculates other components of acid base status. In the 1980s, Canadian physiologist Peter Stewart proposed an alternative approach to acid–base physiology using the physicochemical laws of mass action, conservation of mass and electrical neutrality. The traditional Henderson–Hasselbalch equation-based approach has limitations beyond respiratory derived acid–base disturbances. An ABG can be used to assess adequacy of ventilation and assess the acid base status for a patient. Primary respiratory and metabolic changes have the following characteristics: respiratory acidosis, respiratory alkalosis, metabolic acidosis, and metabolic alkalosis. Actual bicarbonate is the concentration of bicarbonate in the blood. The bicarbonate concentration is derived from the Henderson–Hasselbalch equation.
