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Difficulty: HardPhysiological Adaptation

A client with an unresolved high small bowel obstruction has experienced severe, recurrent emesis for the past 72 hours. During the morning assessment, the nurse observes a respiratory rate of 10 breaths per minute, generalized muscle weakness, and new-onset prominent U waves on the telemetry monitor. Based on these physiological changes, which arterial blood gas (ABG) profile should the nurse identify as most consistent with this client's condition?

  1. pH 7.53, PaCO2 49 mm Hg, HCO3 35 mEq/LAnswer
  2. B
    pH 7.28, PaCO2 32 mm Hg, HCO3 16 mEq/L
  3. C
    pH 7.49, PaCO2 29 mm Hg, HCO3 23 mEq/L
  4. D
    pH 7.30, PaCO2 55 mm Hg, HCO3 25 mEq/L

Answer

pH 7.53, PaCO2 49 mm Hg, HCO3 35 mEq/L
The correct arterial blood gas profile shows a pH of 7.53, PaCO2 of 49 mm Hg, and HCO3 of 35 mEq/L, which indicates a partially compensated metabolic alkalosis. Severe emesis leads to a profound loss of gastric hydrochloric acid, resulting in a primary metabolic alkalosis characterized by a high pH and high bicarbonate. The body attempts to compensate by hypoventilating (evidenced by the respiratory rate of 10 breaths per minute) to retain carbon dioxide, which acts as an acid, thereby pushing the pH back toward normal. This raises the PaCO2 level. Furthermore, the presence of muscle weakness and prominent U waves strongly indicates hypokalemia, which is deeply interlinked with metabolic alkalosis as potassium shifts into cells in exchange for hydrogen ions.

Step-by-Step Solution

1
Analyze the primary pathophysiological event.
The client has experienced severe, recurrent emesis for 72 hours.
Vomiting causes a profound depletion of gastric acid (hydrochloric acid), leading directly to a primary metabolic alkalosis (elevated pH and elevated HCO3).
2
Evaluate the clinical signs for compensatory mechanisms and complications.
The client exhibits a slow respiratory rate (10 breaths/min), generalized muscle weakness, and prominent U waves.
Hypoventilation is the respiratory system's compensatory response to retain carbon dioxide (an acid) to lower the alkaline pH. Muscle weakness and U waves are classic manifestations of hypokalemia, a common complication of metabolic alkalosis due to transcellular shifts and renal potassium wasting.
3
Identify the expected ABG pattern.
The ABG must demonstrate a primary metabolic alkalosis with partial respiratory compensation.
This translates to an alkaline pH (> 7.45), an elevated bicarbonate level (> 26 mEq/L), and an elevated PaCO2 level (> 45 mm Hg).
4
Match the physiological pattern to the provided options.
The profile with pH 7.53, PaCO2 49 mm Hg, and HCO3 35 mEq/L is the only correct match.
This specific combination correctly reflects the primary alkaline state, the elevated bicarbonate from acid loss, and the elevated carbon dioxide resulting from compensatory hypoventilation.

Key Concept

Metabolic alkalosis secondary to severe emesis with compensatory hypoventilation
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Topics

Physiological Adaptation

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