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Difficulty: MediumPhysiological Adaptation

A nurse is monitoring a client admitted with an acute upper gastrointestinal hemorrhage. The client is increasingly restless. Current vital signs are blood pressure 108/86 mm Hg, heart rate 116 beats/min, and respiratory rate 28 breaths/min. Which of the following arterial blood gas (ABG) results represents the expected physiological adaptation during this specific phase of the client's condition?

  1. pH 7.49, PaCO2 30 mm Hg, HCO3- 23 mEq/LAnswer
  2. B
    pH 7.28, PaCO2 36 mm Hg, HCO3- 16 mEq/L
  3. C
    pH 7.31, PaCO2 52 mm Hg, HCO3- 25 mEq/L
  4. D
    pH 7.42, PaCO2 40 mm Hg, HCO3- 24 mEq/L

Answer

The arterial blood gas result demonstrating respiratory alkalosis (elevated pH and decreased PaCO2).
The client's vital signs indicate the early, compensatory stage of hypovolemic shock. This is evidenced by a narrowing pulse pressure (normal is 30-50 mm Hg; the client's is 22 mm Hg), tachycardia, and tachypnea. The rapid respiratory rate (28 breaths/min) causes a 'washout' of carbon dioxide, resulting in a decreased PaCO2 and an appropriately elevated pH. This state of respiratory alkalosis is the body's initial physiological adaptation to maintain oxygenation during acute blood loss.

Step-by-Step Solution

1
Analyze the vital signs to determine the client's current physiological phase.
The pulse pressure is narrow (108 - 86 = 22 mm Hg), heart rate is elevated (116 bpm), and respiratory rate is fast (28/min), indicating the early, compensatory stage of hypovolemic shock.
Identifying the stage of shock is required to anticipate the body's physiological adaptations.
2
Determine the physiological effect of the altered vital signs on gas exchange.
The significant tachypnea (28 breaths/min) leads to excessive exhalation and 'washout' of carbon dioxide.
Carbon dioxide levels directly influence the acid-base balance in the blood.
3
Correlate the physiological change with expected arterial blood gas values.
Decreased carbon dioxide (PaCO2 < 35 mm Hg) results in an elevated pH (> 7.45), which is defined as respiratory alkalosis.
Matching the physiological state to the correct laboratory presentation confirms the primary adaptation.

Key Concept

Compensatory mechanisms in early shock and their direct effect on arterial blood gas values.
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Topics

Physiological Adaptation

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