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Difficulty: EasyPhysiological Adaptation

A young adult client arrives at the emergency department lethargic and exhibiting shallow breathing at a rate of 77 breaths per minute following a suspected narcotic overdose. The laboratory reports the following arterial blood gas values: pH 7.267.26, PaCO2PaCO_2 5858 mm Hg, and HCO3−HCO_3^- 2424 mEq/L. Based on these findings, which acid-base imbalance is the client experiencing?

  1. Respiratory acidosisAnswer
  2. B
    Respiratory alkalosis
  3. C
    Metabolic acidosis
  4. D
    Metabolic alkalosis

Answer

Respiratory acidosis
The client's arterial blood gas results show a pH below 7.357.35, defining an acidotic state. The elevated PaCO2PaCO_2 (greater than 4545 mm Hg) aligns with the acidosis, indicating that the respiratory system is the source of the disturbance due to hypoventilation from the suspected narcotic overdose. The normal bicarbonate (HCO3−HCO_3^-) level confirms it is uncompensated respiratory acidosis.

Step-by-Step Solution

1
Analyze the pH value to determine the primary state of the blood.
The pH is 7.267.26, which is lower than the normal range of 7.357.35 to 7.457.45, indicating acidemia.
Determining whether the blood is acidic or alkalotic is the fundamental first step in interpreting arterial blood gases.
2
Evaluate the PaCO2PaCO_2 level to check for a respiratory component.
The PaCO2PaCO_2 is 5858 mm Hg, which is higher than the normal range of 3535 to 4545 mm Hg.
An elevated PaCO2PaCO_2 in the presence of an acidic pH indicates that the lungs are retaining carbon dioxide, pointing to a respiratory cause for the acidosis.
3
Examine the HCO3−HCO_3^- level to check for metabolic involvement or compensation.
The HCO3−HCO_3^- is 2424 mEq/L, which falls squarely within the normal range of 2222 to 2626 mEq/L.
A normal bicarbonate level confirms that the acidosis is strictly respiratory in origin and that the kidneys have not yet begun to compensate for the imbalance.

Key Concept

Interpretation of uncompensated respiratory acidosis resulting from hypoventilation.
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Physiological Adaptation

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