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Difficulty: MediumPhysiological Adaptation

A telemetry nurse is called to the room of a client who suffered a comminuted pelvic fracture seventy-two hours prior. The client is suddenly grasping their chest, expressing a severe feeling of doom, and sweating profusely. Assessment reveals a heart rate of 138138 beats per minute, a respiratory rate of 3434 breaths per minute, and a blood pressure of 98/76 mm Hg98/76 \text{ mm Hg}. Room air pulse oximetry displays an oxygen saturation of 85%85\%. The rapid arterial blood gas (ABG) results are as follows: pH=7.53\text{pH} = 7.53, PaCO2=29 mm Hg\text{PaCO}_2 = 29 \text{ mm Hg}, HCO3−=24 mEq/L\text{HCO}_3^- = 24 \text{ mEq/L}, and PaO2=56 mm Hg\text{PaO}_2 = 56 \text{ mm Hg}. Which of the following conclusions accurately reflects this client's current physiological derangement?

  1. Uncompensated respiratory alkalosis with severe hypoxemia, indicating a probable pulmonary embolism.Answer
  2. B
    Uncompensated respiratory acidosis with hypoxemia, indicating the rapid onset of acute respiratory failure.
  3. C
    Fully compensated metabolic alkalosis, reflecting the body's compensatory response to acute pain and anxiety.
  4. D
    Metabolic acidosis with a widened pulse pressure, indicating early hemorrhagic shock from the pelvic fracture.

Answer

The client is experiencing uncompensated respiratory alkalosis and severe hypoxemia, which strongly suggests a pulmonary embolism.
The arterial blood gas results demonstrate an elevated pH (alkalosis) driven by a decreased PaCO2 (respiratory origin). The normal bicarbonate level indicates there is no metabolic compensation yet. This state of uncompensated respiratory alkalosis, paired with profound hypoxemia (low PaO2), sudden feeling of doom, and severe tachycardia in a client with a recent pelvic fracture, is the classic clinical presentation of a pulmonary embolism causing dead-space ventilation and resultant hyperventilation.

Step-by-Step Solution

1
Evaluate the pH value to determine the primary acid-base status.
The pH\text{pH} is 7.537.53.
A pH greater than 7.45 indicates alkalosis.
2
Analyze the respiratory and metabolic components to find the cause.
The PaCO2\text{PaCO}_2 is low at 29 mm Hg29 \text{ mm Hg}, and the HCO3−\text{HCO}_3^- is normal at 24 mEq/L24 \text{ mEq/L}.
A low carbon dioxide level perfectly aligns with an alkaline pH, indicating a primary respiratory alkalosis. The normal bicarbonate level indicates the kidneys have not yet initiated compensation.
3
Analyze oxygenation and vital sign trends to determine the underlying pathology.
The PaO2\text{PaO}_2 is 56 mm Hg56 \text{ mm Hg}, accompanied by a narrowed pulse pressure (22 mm Hg22 \text{ mm Hg}), tachycardia, and tachypnea.
Severe hypoxemia combined with sudden chest pain, tachypnea, and a history of pelvic fracture points directly to a massive pulmonary embolism causing right ventricular strain and hyperventilation.

Key Concept

Arterial Blood Gas Interpretation and Pulmonary Embolism Recognition
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Topics

Physiological Adaptation

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