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Difficulty: MediumPhysiological Adaptation

During a shift assessment, the nurse notes that a client with a severe intestinal infection has produced copious, watery stools for three consecutive days. The healthcare team suspects an acid-base derangement and draws an arterial blood gas (ABG) sample. Which of the following ABG parameters would confirm a diagnosis of uncompensated metabolic acidosis? Select all that apply.

  1. pH of 7.29Answer
  2. PaCO2PaCO_2 of 39 mm HgAnswer
  3. HCO3−HCO_3^- of 16 mEq/LAnswer
  4. D
    pH of 7.48
  5. E
    PaCO2PaCO_2 of 31 mm Hg
  6. F
    HCO3−HCO_3^- of 30 mEq/L

Answer

The expected parameters are a pH of 7.29, a PaCO2PaCO_2 of 39 mm Hg, and an HCO3−HCO_3^- of 16 mEq/L.
Severe diarrhea results in the loss of alkaline intestinal secretions (bicarbonate), leading to metabolic acidosis. This is indicated by a pH less than 7.35 and a primary decrease in HCO3−HCO_3^- to less than 22 mEq/L. Because the condition is uncompensated, the respiratory system has not yet altered the ventilation rate to normalize the pH; therefore, the PaCO2PaCO_2 remains within the normal range of 35-45 mm Hg.

Step-by-Step Solution

1
Identify the primary disturbance caused by the clinical scenario.
Severe diarrhea causes an excessive loss of bicarbonate from the lower gastrointestinal tract, leading to a state of metabolic acidosis.
Understanding the physiological effect of the fluid loss is necessary to determine the expected primary acid-base imbalance.
2
Determine the expected ABG parameters for the primary disturbance.
Metabolic acidosis is characterized by an acidic pH (less than 7.35) and a low bicarbonate level (less than 22 mEq/L).
This establishes the core laboratory findings required to diagnose the primary condition.
3
Evaluate the state of compensation.
The scenario specifies an 'uncompensated' state, meaning the compensatory mechanism (respiratory PaCO2PaCO_2) remains within the normal range of 35-45 mm Hg.
An abnormal PaCO2PaCO_2 would indicate that partial or full compensation had begun.

Key Concept

Uncompensated Metabolic Acidosis
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Topics

Physiological Adaptation

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