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Difficulty: MediumPhysiological Adaptation

A nurse is caring for a client who has been experiencing severe, persistent vomiting for the past 48 hours. Which of the following arterial blood gas (ABG) and clinical assessment findings should the nurse anticipate?

  1. pH 7.50, PaCO2 42 mm Hg, HCO3 34 mEq/L; accompanied by muscle cramping and tingling in the extremities.Answer
  2. B
    pH 7.28, PaCO2 35 mm Hg, HCO3 16 mEq/L; accompanied by deep, rapid respirations.
  3. C
    pH 7.31, PaCO2 55 mm Hg, HCO3 26 mEq/L; accompanied by lethargy and confusion.
  4. D
    pH 7.48, PaCO2 28 mm Hg, HCO3 22 mEq/L; accompanied by dizziness and circumoral numbness.

Answer

pH 7.50, PaCO2 42 mm Hg, HCO3 34 mEq/L; accompanied by muscle cramping and tingling in the extremities.
The correct answer identifies the ABG parameters for metabolic alkalosis (pH 7.50, HCO3 34 mEq/L) which is the direct result of losing gastric acid through persistent vomiting. Furthermore, it correctly pairs this with the clinical signs of neuromuscular excitability (cramping, tingling), which occur because alkalosis causes a functional hypocalcemia by increasing calcium binding to serum proteins.

Step-by-Step Solution

1
Identify the primary acid-base disturbance caused by the clinical scenario.
Severe vomiting causes significant loss of hydrochloric acid (HCl) from the stomach.
Loss of acid from the upper gastrointestinal tract directly leads to an increase in blood pH and a relative excess of bicarbonate, causing metabolic alkalosis.
2
Determine the expected ABG values for the identified disturbance.
Metabolic alkalosis is characterized by an elevated pH (> 7.45) and an elevated HCO3 (> 26 mEq/L). PaCO2 may be normal or slightly elevated due to compensatory hypoventilation.
This helps eliminate options presenting with acidosis or primary respiratory disturbances.
3
Correlate the acid-base imbalance with expected physiological assessment findings.
Metabolic alkalosis increases the binding of calcium to albumin, reducing the fraction of free ionized calcium in the blood.
Decreased ionized calcium (hypocalcemia) manifests clinically as neuromuscular irritability, including muscle cramping, tetany, and tingling (paresthesia).

Key Concept

Severe, persistent vomiting causes a loss of gastric acid (hydrogen ions), resulting in metabolic alkalosis. This alkalotic state induces a relative hypocalcemia by increasing calcium binding to albumin, which clinically presents as neuromuscular excitability.
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Physiological Adaptation

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