ABG
Formal Definition
Arterial blood gas: a blood test obtained from an artery (usually radial) measuring pH, partial pressures of oxygen (PaO2) and carbon dioxide (PaCO2), bicarbonate (HCO3−), and oxygen saturation (SaO2) to assess respiratory and metabolic acid-base status.
How It's Used on the Ward
"Get an ABG" or "ABG shows she's in resp failure" — the definitive bedside test for oxygenation, ventilation, and acid-base balance.
Example
""Patient in respiratory distress: ABG shows pH 7.22, PCO2 58, PaO2 54 on 6L NC. That's acute hypercapnic respiratory failure with hypoxemia — BiPAP now, anesthesia on standby.""
Clinical Context
ABG interpretation: pH first (acidosis/alkalosis), then PCO2 (respiratory component), then HCO3 (metabolic component), then determine if compensation is appropriate. A VBG (venous blood gas) is acceptable for pH and PCO2 trending in most situations and doesn't require arterial puncture — use ABG when precise PaO2 matters (oxygenation assessment, FiO2 titration).
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