Acid-Base Disorders: Rapid Interpretation

An arterial blood gas (ABG) is a snapshot of three linked quantities: the acidity of the blood (pH), the carbon dioxide the lungs are clearing (PaCO₂), and the bicarbonate the kidneys and body chemistry are holding (HCO₃⁻). Acid-base disorders occur when physiological processes disturb the balance between hydrogen ions, bicarbonate and carbon dioxide. Reading an ABG is not a memory exercise. It is a short sequence of questions: is the blood acidemic or alkalemic, which number moved first, is the body compensating the way it should, and is there a second problem hiding in the numbers? The nursing question that sits on top of all of them is simpler and more important: is this patient getting worse? The result is only useful when it is read beside the patient in the bed. Treat the deteriorating patient, not the ABG in isolation. A patient scenario shows why. A 68-year-old patient with COPD becomes increasingly drowsy after receiving an opioid analgesic. Respirations are shallow at 8/min. The ABG shows pH 7.24, PaCO₂ 68 mmHg, HCO₃⁻ 28 mmol/L and PaO₂ 62 mmHg. The...