2025 – PAGE 366 – ACID-BASE DISORDERS

ABG & CHEMISTRY PEARLS

• If the bicarb is not normal, there is SOME TYPE of acid base disturbance.
• If the bicarb level is low, it’s due to a metabolic acidosis. This could be a gap or a non-gap acidosis. If it’s a non-gap acidosis, that could be a primary disturbance, or it could be due to compensation.
• If your patient has a positive anion gap on the chemistry panel (meaning a gap > 12), then there is at least a primary anion gap metabolic acidosis. Don’t forget to take the albumin into account when evaluating the gap. Also, you have to look at the ABG to see if this acidosis is the overarching acid-base disorder or if it is an additional primary disorder in a mixed acid-base disturbance.

ABG & CHEMISTRY SHORTCUTS

• A chloride < 80 means there is at least a concurrent primary metabolic alkalosis present.
• A pCO2 > 55 means there is at least a concurrent primary respiratory acidosis present (because the body is unable to compensate for a metabolic alkalosis beyond 55).
• A bicarb > 40 means there is at least a concurrent primary metabolic alkalosis (because the body is unable to compensate beyond 40 for a respiratory acidosis).
• A bicarb < 12 means there is at least a concurrent primary metabolic acidosis (because the body is unable to compensate beyond 12 for a respiratory alkalosis).
• If the overarching diagnosis is a metabolic acidosis, you should expect to see a low bicarb level on the chemistry. If it’s NOT low, then there’s too additional base in the system that doesn’t belong there. Is the bicarb level HIGHER than 24? If so, there is an additional primary metabolic alkalosis! In this situation, even a normal bicarbonate level of 24 can be representative of excess base in the system.
• In an overarching metabolic alkalosis, the bicarbonate level should be HIGH. If the patient’s ABG reveals an overarching metabolic alkalosis but the bicarbonate level is around 24, then there is an additional primary metabolic acidosis present. If only one answer choice has metabolic alkalosis and a metabolic acidosis of some kind, you’re done!

That’s it! You’re now an ABG ninja!