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Difficulty: MediumPhysiological Adaptation

A nurse is evaluating a client who has been receiving continuous nasogastric tube suctioning for the past 72 hours due to a mechanical small bowel obstruction. During the morning assessment, the client exhibits shallow respirations, bilateral muscle twitching, and a heart rate of 110 beats per minute. Which of the following arterial blood gas (ABG) results best correlates with this client's current clinical presentation?

  1. pH 7.52, PaCO2PaCO_2 48 mm Hg, HCO3−HCO_3^- 32 mEq/LAnswer
  2. B
    pH 7.28, PaCO2PaCO_2 55 mm Hg, HCO3−HCO_3^- 26 mEq/L
  3. C
    pH 7.31, PaCO2PaCO_2 38 mm Hg, HCO3−HCO_3^- 18 mEq/L
  4. D
    pH 7.49, PaCO2PaCO_2 28 mm Hg, HCO3−HCO_3^- 24 mEq/L

Answer

pH 7.52, PaCO2PaCO_2 48 mm Hg, HCO3−HCO_3^- 32 mEq/L
Continuous removal of gastric acid via nasogastric suctioning leads to metabolic alkalosis, evidenced by an elevated pH (7.52) and elevated bicarbonate (HCO3−HCO_3^- 32 mEq/L). The body attempts to compensate for this alkalosis by hypoventilating (shallow respirations) to retain carbon dioxide, which explains the elevated PaCO2PaCO_2 (48 mm Hg). Furthermore, the client's muscle twitching is a classic sign of associated hypocalcemia or hypokalemia, both of which are common complications of metabolic alkalosis.

Step-by-Step Solution

1
Identify the primary acid-base disturbance caused by prolonged nasogastric suctioning.
Loss of gastric acid (hydrochloric acid) leads to a primary metabolic alkalosis.
The stomach contains high levels of acid; removing it systematically increases the relative amount of circulating base (bicarbonate) in the blood.
2
Determine the expected compensatory physiological response to metabolic alkalosis.
The respiratory system compensates by decreasing the rate and depth of respirations (hypoventilation) to retain CO2CO_2.
Retaining carbon dioxide (an acid) helps lower the elevated blood pH back toward the normal physiological range. This explains the client's shallow respirations.
3
Analyze the ABG options to find the one matching metabolic alkalosis with partial respiratory compensation.
The correct ABG values will show an elevated pH, elevated HCO3−HCO_3^-, and elevated PaCO2PaCO_2.
A pH of 7.52 (alkalemia) with an HCO3−HCO_3^- of 32 mEq/L confirms the metabolic origin, while a PaCO2PaCO_2 of 48 mm Hg confirms respiratory compensation.

Key Concept

Metabolic Alkalosis and Respiratory Compensation
Estimated Time:1m 30s
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Topics

Physiological Adaptation

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