This first part of a three-part series explains the basic principles of blood gas analysis, its interpretation, and common abnormalities. Blood gas analysis is essential for assessing respiratory insufficiency, which may be type 1 (hypoxemia with low CO₂) or type 2 (hypercapnia due to ventilatory failure). It evaluates ventilation, oxygenation, circulation, and acid-base balance. Results must be interpreted with clinical context, environmental data, and additional tests. Normal arterial values are roughly PaO₂ 70–100 mmHg, PaCO₂ 35–45 mmHg, and pH 7.35–7.45. Oxygen transport depends mainly on hemoglobin and cardiac output. Hypoxemia may result from hypoventilation, diffusion problems, V/Q mismatch, or shunts, while hypercapnia is typically caused by reduced ventilation or increased dead space.
