Key Concepts
Introduction
Arterial blood gas (ABG) analysis provides critical information about a patient's acid-base balance, oxygenation, and ventilation status. The normal ABG values โ pH 7.35-7.45, PaCO2 35-45 mmHg, PaO2 80-100 mmHg, HCO3 22-26 mEq/L, and SaO2 95-100% โ represent the body's tightly regulated homeostatic mechanisms. Respiratory acidosis (pH < 7.35, PaCO2 > 45) results from hypoventilation, while respiratory alkalosis (pH > 7.45, PaCO2 < 35) results from hyperventilation. Metabolic acidosis (pH < 7.35, HCO3 < 22) occurs from bicarbonate loss or acid accumulation, while metabolic alkalosis (pH > 7.45, HCO3 > 26) occurs from acid loss or bicarbonate excess. Compensation occurs when the opposing system attempts to normalize pH. On the exam, writers often pair stable-sounding options with unstable dataโnotice the mismatch before you commit. If the stem names a license or role, reread that line; scope errors are classic trap answers even when the clinical topic is familiar. Run a 60-second scan: breathing work and oxygenation, perfusion and end organs, neuro baseline, likely infection sources, and devices that can fail quietly. When two answers feel partly right, pick the one...