interpret an ABG
Interpreting an ABG is something you’ll have to do on a daily basis in the MICU. The most important thing is to have a method that you like and can remember, and to use it every time you review an ABG. The handout on this page explains an easy-to-use method, but it’s not the only way and certainly doesn’t claim to be the best.
There are three basic steps to ABG interpretation:
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Determine the primary disorder (respiratory or metabolic, alkalosis or acidosis).
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See if the compensation is adequate or inadequate; if it’s not adequate, then there is another disorder present.
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Use the Anion Gap to see if an organic acidosis is present. If the anion gap is higher than normal, then a metabolic organic acidosis must be happening.
Common Causes of Respiratory Acidosis
Drug overdose
COPD exacerbation
Pneumonia
Septic shock
Neuromuscular disease
Common Causes of Respiratory Alkalosis
Pain and anxiety
Fever
Sepsis
Pulmonary embolism
Common Causes of Metabolic Alkalosis
Intravascular volume depletion
Vomiting or nasogastric suctioning
Diuretics
Common Causes of Metabolic Acidosis
(with an elevated anion gap)
Methanol
Uremia
Diabetic ketoacidosis
Paraldehyde
Iron, Isoniazid
Lactic acidosis
Ethylene glycol, Ethanol-related ketoacidosis
Salicylates, Starvation ketoacidosis, Sepsis
Common Causes of Metabolic Acidosis
(without an elevated anion gap)
Hyperchloremia, Hyperalimentation
Acetazolamide, Addison’s disease
Renal tubular acidosis
Diarrhea
Ureteral diversion (ureterosigmoidostomy, ureterostomy)
Pancreatic problems (pancreaticoduodenal fistula, pancreatic pseudocyst)