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Difficulty: MediumPhysiological Adaptation

A nurse is caring for a client who has been receiving continuous gastric suctioning via a nasogastric (NG) tube for the past 72 hours due to a mechanical bowel obstruction. During the morning assessment, the client reports muscle cramps and a tingling sensation in the fingertips. Based on the client's clinical presentation and current therapy, which of the following arterial blood gas (ABG) results should the nurse anticipate?

  1. pH 7.50, PaCO2 48 mm Hg, HCO3 32 mEq/LAnswer
  2. B
    pH 7.31, PaCO2 36 mm Hg, HCO3 16 mEq/L
  3. C
    pH 7.49, PaCO2 28 mm Hg, HCO3 24 mEq/L
  4. D
    pH 7.33, PaCO2 54 mm Hg, HCO3 28 mEq/L

Answer

The ABG values indicating metabolic alkalosis with partial respiratory compensation (elevated pH, elevated HCO3, and elevated PaCO2).
Prolonged nasogastric suctioning depletes the body of gastric secretions, which are rich in hydrochloric acid, potassium, and sodium. The loss of acid leads to a primary metabolic alkalosis, characterized by an elevated pH (> 7.45) and an elevated bicarbonate (HCO3 > 26 mEq/L). The body attempts to compensate by decreasing the respiratory rate to retain carbon dioxide, leading to an elevated PaCO2 (> 45 mm Hg). Furthermore, metabolic alkalosis decreases ionized calcium levels in the blood, which causes the neuromuscular excitability manifested as muscle cramps and tingling (paresthesia). The correct option presents the exact parameters of metabolic alkalosis with partial respiratory compensation.

Step-by-Step Solution

1
Identify the primary physiological impact of continuous nasogastric suctioning.
Gastric contents are highly acidic due to hydrochloric acid. Continuous removal leads to a significant loss of hydrogen ions.
Understanding the fluid being lost determines the resulting acid-base imbalance.
2
Determine the expected acid-base imbalance from the loss of stomach acid.
Loss of body acid results in an accumulation of base (bicarbonate), leading to metabolic alkalosis. This is characterized by an elevated pH (> 7.45) and elevated HCO3 (> 26 mEq/L).
Acid loss directly raises blood pH and increases the relative concentration of bicarbonate.
3
Analyze the client's symptoms of muscle cramps and tingling.
Alkalosis causes increased binding of calcium to albumin, reducing ionized calcium levels in the blood. Hypocalcemia causes neuromuscular excitability, explaining the cramps and tingling.
Correlating clinical signs with the anticipated physiological state confirms the metabolic disturbance.
4
Evaluate the ABG options to find the one representing metabolic alkalosis.
The option with pH 7.50 and HCO3 32 mEq/L represents metabolic alkalosis. The elevated PaCO2 of 48 mm Hg shows the lungs are attempting to compensate by retaining acid (CO2).
Selecting the specific laboratory values that match the deduced clinical condition.

Key Concept

Acid-Base Imbalances: Metabolic Alkalosis from Gastric Loss
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Topics

Physiological Adaptation

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