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Difficulty: MediumPhysiological Adaptation

A client is receiving continuous nasogastric suctioning for a mechanical bowel obstruction. On the third day of treatment, the client reports numbness around the mouth and tingling in the extremities. Upon further assessment, the nurse notes a positive Chvostek sign. Which arterial blood gas (ABG) values correlate most accurately with this clinical presentation?

  1. pH 7.52, PaCO2 46 mm Hg, HCO3- 34 mEq/LAnswer
  2. B
    pH 7.28, PaCO2 38 mm Hg, HCO3- 16 mEq/L
  3. C
    pH 7.31, PaCO2 56 mm Hg, HCO3- 25 mEq/L
  4. D
    pH 7.54, PaCO2 28 mm Hg, HCO3- 23 mEq/L

Answer

The ABG values showing pH 7.52, PaCO2 46 mm Hg, and HCO3- 34 mEq/L represent partially compensated metabolic alkalosis, which is the expected consequence of continuous gastric suction.
The correct ABG values demonstrate metabolic alkalosis (pH 7.52, HCO3- 34 mEq/L). Continuous nasogastric suction removes hydrochloric acid from the stomach, leading to a surplus of bicarbonate in the blood. Alkalosis causes an increase in calcium binding to plasma proteins, resulting in a decrease in ionized calcium. This secondary hypocalcemia manifests as neuromuscular excitability, including numbness, tingling, and a positive Chvostek sign.

Step-by-Step Solution

1
Analyze the clinical mechanism of continuous nasogastric suctioning.
Identify that stomach fluid is highly acidic (rich in hydrochloric acid). Continuous removal leads to a significant loss of body acid.
Understanding the source of fluid loss determines the primary acid-base disturbance.
2
Determine the resulting primary acid-base imbalance.
Loss of acid from the upper GI tract causes a primary metabolic alkalosis, characterized by an elevated pH (> 7.45) and an elevated HCO3- (> 26 mEq/L).
Metabolic alkalosis is confirmed when both pH and bicarbonate levels are above normal parameters.
3
Correlate the physical assessment findings (numbness, tingling, positive Chvostek sign).
Recognize these as classic signs of hypocalcemia.
In an alkalotic state, hydrogen ions detach from albumin to help buffer the blood, which allows more calcium to bind to the empty spaces on the albumin. This decreases free ionized calcium levels, causing hypocalcemia.
4
Select the ABG profile that matches metabolic alkalosis.
Select the option with pH 7.52 (alkalemia) and HCO3- 34 mEq/L (metabolic source), with a slight increase in PaCO2 indicating partial respiratory compensation.
This is the only laboratory profile that physiologically aligns with both the intervention (suctioning) and the resulting clinical signs.

Key Concept

Metabolic alkalosis and secondary hypocalcemia related to gastric acid loss.
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Topics

Physiological Adaptation

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