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Difficulty: EasyNephrology

Review the following arterial blood gas (ABG) profiles obtained on room air. Match each laboratory ABG profile with its most likely corresponding primary acid-base disorder.

  • pH 7.257.25, PaCO2PaCO_2 6060 mmHg, HCO3−HCO_3^- 2626 mEq/LRespiratory acidosis
  • pH 7.307.30, PaCO2PaCO_2 3030 mmHg, HCO3−HCO_3^- 1414 mEq/LMetabolic acidosis
  • pH 7.507.50, PaCO2PaCO_2 4040 mmHg, HCO3−HCO_3^- 3232 mEq/LMetabolic alkalosis
  • pH 7.557.55, PaCO2PaCO_2 2525 mmHg, HCO3−HCO_3^- 2222 mEq/LRespiratory alkalosis

Answer

pH 7.25, PaCO2 60 matches with Respiratory acidosis. pH 7.30, PaCO2 30 matches with Metabolic acidosis. pH 7.50, PaCO2 40 matches with Metabolic alkalosis. pH 7.55, PaCO2 25 matches with Respiratory alkalosis.
Each arterial blood gas profile uniquely demonstrates one of the four primary simple acid-base disorders by pairing the pH directional shift (acidemia or alkalemia) with the corresponding primary derangement in either PaCO2PaCO_2 (respiratory) or bicarbonate (metabolic).

Step-by-Step Solution

1
Evaluate the first ABG profile (pH 7.257.25, PaCO2PaCO_2 6060, HCO3−HCO_3^- 2626).
Matches with Respiratory acidosis.
A pH below 7.357.35 defines acidemia. The high PaCO2PaCO_2 matches the acidic direction, identifying it as the primary disorder.
2
Evaluate the second ABG profile (pH 7.307.30, PaCO2PaCO_2 3030, HCO3−HCO_3^- 1414).
Matches with Metabolic acidosis.
A pH below 7.357.35 defines acidemia. The low HCO3−HCO_3^- matches the acidic direction, while the low PaCO2PaCO_2 represents respiratory compensation.
3
Evaluate the third ABG profile (pH 7.507.50, PaCO2PaCO_2 4040, HCO3−HCO_3^- 3232).
Matches with Metabolic alkalosis.
A pH above 7.457.45 defines alkalemia. The high HCO3−HCO_3^- directly matches the alkalemic direction.
4
Evaluate the fourth ABG profile (pH 7.557.55, PaCO2PaCO_2 2525, HCO3−HCO_3^- 2222).
Matches with Respiratory alkalosis.
A pH above 7.457.45 defines alkalemia. The low PaCO2PaCO_2 directly matches the alkalemic direction.

Key Concept

Basic Interpretation of Arterial Blood Gases
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Topics

Nephrology

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