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Difficulty: MediumReduction of Risk Potential

A nurse is evaluating the arterial blood gas (ABG) results of a client with severe hyperemesis gravidarum who has experienced intractable vomiting for the past 48 hours. The client appears lethargic, and the respiratory rate is currently 10 breaths per minute. To accurately assess the client's risk for physiological decompensation, which ABG pattern should the nurse anticipate?

  1. pH 7.52, PaCO2 49 mm Hg, HCO3 32 mEq/LAnswer
  2. B
    pH 7.28, PaCO2 50 mm Hg, HCO3 24 mEq/L
  3. C
    pH 7.31, PaCO2 35 mm Hg, HCO3 16 mEq/L
  4. D
    pH 7.48, PaCO2 30 mm Hg, HCO3 22 mEq/L

Answer

pH 7.52, PaCO2 49 mm Hg, HCO3 32 mEq/L
The correct answer displays a high pH (alkalosis) and a high HCO3 (metabolic origin), which directly aligns with the severe loss of gastric acid from continuous vomiting. Furthermore, the elevated PaCO2 correctly reflects the respiratory system's compensatory mechanism (hypoventilation, as evidenced by a respiratory rate of 10) attempting to restore balance by retaining acidic CO2.

Step-by-Step Solution

1
Identify the primary source of volume and electrolyte loss.
Intractable vomiting causes a significant loss of hydrochloric acid (HCl) from the stomach.
Understanding the clinical cause dictates the primary acid-base imbalance.
2
Determine the resulting primary acid-base imbalance.
The extensive loss of stomach acid leads to a primary metabolic alkalosis.
Metabolic alkalosis is characterized by an elevated pH (> 7.45) and an elevated HCO3 (> 26 mEq/L).
3
Analyze the client's respiratory rate for evidence of physiological compensation.
The respiratory rate of 10 breaths per minute indicates hypoventilation.
The body attempts to compensate for metabolic alkalosis by slowing respirations to retain CO2 (an acidic gas), which subsequently elevates the PaCO2 level (> 45 mm Hg).
4
Select the ABG values that match these physiological mechanisms.
The only ABG pattern showing an elevated pH, elevated HCO3, and elevated PaCO2 is pH 7.52, PaCO2 49 mm Hg, HCO3 32 mEq/L.
This confirms a state of partially compensated metabolic alkalosis.

Key Concept

Acid-Base Imbalances and Compensatory Mechanisms
Estimated Time:1m 15s
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Reduction of Risk Potential

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