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Difficulty: MediumPhysiological Adaptation

A client with a recent diagnosis of Guillain-Barré syndrome is being closely monitored on the medical-surgical unit. The nurse observes that the client is becoming increasingly lethargic, and their respiratory rate has decreased to 8 breaths per minute with weak chest wall movement. Based on these clinical findings, which of the following arterial blood gas (ABG) results should the nurse most anticipate?

  1. pH 7.25, PaCO2PaCO_2 62 mm Hg, HCO3−HCO_3^- 24 mEq/LAnswer
  2. B
    pH 7.48, PaCO2PaCO_2 28 mm Hg, HCO3−HCO_3^- 23 mEq/L
  3. C
    pH 7.31, PaCO2PaCO_2 36 mm Hg, HCO3−HCO_3^- 16 mEq/L
  4. D
    pH 7.49, PaCO2PaCO_2 42 mm Hg, HCO3−HCO_3^- 32 mEq/L

Answer

The ABG result showing pH 7.25, PaCO2PaCO_2 62 mm Hg, and HCO3−HCO_3^- 24 mEq/L, indicating acute respiratory acidosis.
The correct answer displays uncompensated respiratory acidosis. Guillain-Barré syndrome can lead to progressive neuromuscular weakness, eventually affecting the muscles of respiration. A respiratory rate of 8 breaths per minute with weak chest excursions indicates severe hypoventilation, which causes the body to retain carbon dioxide. This rapid accumulation of carbon dioxide (PaCO2PaCO_2 > 45 mm Hg) drives the blood pH down into an acidotic state (pH < 7.35). Because this is an acute change, the kidneys have not yet retained bicarbonate (HCO3−HCO_3^-) to compensate, leaving it within the normal range (22-26 mEq/L).

Step-by-Step Solution

1
Analyze the client's clinical presentation.
The client has Guillain-Barré syndrome, is lethargic, and is hypoventilating with a respiratory rate of 8 breaths per minute and weak chest movement.
Understanding the physiological impact of the disease process helps predict the resulting acid-base imbalance.
2
Determine the physiological consequence of hypoventilation.
Inadequate ventilation leads to the retention of carbon dioxide (CO2CO_2) in the lungs and bloodstream.
CO2CO_2 acts as an acid in the body, so accumulating CO2CO_2 drives the blood pH lower.
3
Correlate the physiological change with expected ABG values.
The expected ABG will show a low pH (acidosis), an elevated PaCO2PaCO_2 (respiratory origin), and a normal HCO3−HCO_3^- since the kidneys have not had time to compensate.
This combination of values precisely defines uncompensated respiratory acidosis.

Key Concept

Arterial Blood Gas (ABG) Interpretation in Neuromuscular Respiratory Failure
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Topics

Physiological Adaptation

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