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Difficulty: MediumPhysiological Adaptation

An adult client who missed three consecutive hemodialysis treatments is admitted to the medical unit with profound fatigue and deep, rapid breathing. An arterial blood gas (ABG) analysis yields the following results: pH 7.257.25, PaCO 2_2 2929 mm Hg, HCO 3−_3^- 1414 mEq/L, and PaO 2_2 9292 mm Hg. Which of the following physiological mechanisms best explains this client's respiratory pattern?

  1. The lungs are increasing ventilation to excrete carbon dioxide as a compensatory response to metabolic acidosis.Answer
  2. B
    The respiratory center is depressed by uremic toxins, causing carbon dioxide retention and primary respiratory acidosis.
  3. C
    The kidneys' failure to synthesize bicarbonate has resulted in a primary respiratory alkalosis.
  4. D
    The respiratory system is maximizing oxygen intake to reverse severe tissue hypoxia and prevent anaerobic metabolism.

Answer

The correct answer states that the lungs are increasing ventilation to excrete carbon dioxide as a compensatory response to metabolic acidosis.
The client's missed hemodialysis sessions have led to a buildup of metabolic acids, evident by the low pH (7.257.25) and low bicarbonate (1414 mEq/L), which signifies metabolic acidosis. The deep, rapid breathing (Kussmaul respirations) is the body's compensatory mechanism to excrete carbon dioxide (which acts as an acid in the body), thereby lowering the PaCO 2_2 to 2929 mm Hg in an attempt to normalize the blood pH.

Step-by-Step Solution

1
Analyze the client's clinical presentation and history.
Missing consecutive hemodialysis sessions leads to the retention of metabolic waste products and acids, causing metabolic acidosis. The deep, rapid breathing pattern represents Kussmaul respirations.
To identify the underlying pathophysiology causing the client's distress.
2
Interpret the arterial blood gas (ABG) values.
A pH of 7.25 indicates acidemia. A low HCO3- of 14 mEq/L confirms the primary disorder is metabolic acidosis.
To accurately diagnose the primary acid-base imbalance based on objective data.
3
Evaluate the respiratory ABG values in the context of the clinical signs.
The PaCO2 is low (29 mm Hg), indicating the lungs are hyperventilating to blow off carbon dioxide (an acid) to compensate for the metabolic acidosis. The PaO2 is normal (92 mm Hg), ruling out hypoxia as the driver.
To link the physiological mechanism of Kussmaul respirations to the specific ABG findings.

Key Concept

Metabolic Acidosis and Respiratory Compensation
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Topics

Physiological Adaptation

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