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Difficulty: MediumPhysiological Adaptation

A nurse on a medical-surgical unit is evaluating a client with end-stage renal disease who was admitted after missing multiple scheduled hemodialysis sessions. The client appears lethargic and exhibits deep, rapid respirations. Based on this clinical presentation, which of the following arterial blood gas (ABG) results is most expected?

  1. A
    pH=7.25\text{pH} = 7.25, PaCO2=55 mm Hg\text{PaCO}_2 = 55 \text{ mm Hg}, HCO3−=26 mEq/L\text{HCO}_3^- = 26 \text{ mEq/L}
  2. B
    pH=7.26\text{pH} = 7.26, PaCO2=42 mm Hg\text{PaCO}_2 = 42 \text{ mm Hg}, HCO3−=16 mEq/L\text{HCO}_3^- = 16 \text{ mEq/L}
  3. pH=7.28\text{pH} = 7.28, PaCO2=30 mm Hg\text{PaCO}_2 = 30 \text{ mm Hg}, HCO3−=15 mEq/L\text{HCO}_3^- = 15 \text{ mEq/L}Answer
  4. D
    pH=7.49\text{pH} = 7.49, PaCO2=44 mm Hg\text{PaCO}_2 = 44 \text{ mm Hg}, HCO3−=32 mEq/L\text{HCO}_3^- = 32 \text{ mEq/L}

Answer

The expected arterial blood gas result is pH=7.28\text{pH} = 7.28, PaCO2=30 mm Hg\text{PaCO}_2 = 30 \text{ mm Hg}, and HCO3−=15 mEq/L\text{HCO}_3^- = 15 \text{ mEq/L}.
Missing scheduled hemodialysis leads to an accumulation of metabolic waste products and acids, resulting in metabolic acidosis (characterized by a low pH and a low HCO3−\text{HCO}_3^-). In response to the acidic environment, the central chemoreceptors stimulate the respiratory center, causing the client to increase the depth and rate of respirations (Kussmaul respirations). This compensatory hyperventilation expels excess carbon dioxide (CO2\text{CO}_2), which lowers the PaCO2\text{PaCO}_2. The correct ABG reflects this exact physiological state: an acidemic pH (7.28), a low bicarbonate indicating the metabolic source (15 mEq/L), and a compensatory decrease in carbon dioxide (30 mm Hg).

Step-by-Step Solution

1
Identify the primary acid-base disturbance.
Missed hemodialysis causes retention of uremic waste and metabolic acids, leading to metabolic acidosis (decreased pH and decreased HCO3-).
The kidneys are unable to excrete hydrogen ions or regenerate bicarbonate.
2
Analyze the physical assessment findings.
The client is exhibiting deep, rapid respirations, known as Kussmaul respirations.
This is a classic symptom of severe metabolic acidosis.
3
Determine the physiological consequence of the symptoms.
Hyperventilation effectively blows off carbon dioxide (CO2), lowering the PaCO2 in the blood.
The respiratory system is attempting to compensate for the metabolic acidosis by inducing a mild respiratory alkalosis.
4
Select the matching ABG values.
The correct ABG must show low pH (< 7.35), low HCO3- (< 22 mEq/L), and low PaCO2 (< 35 mm Hg).
These values collectively indicate metabolic acidosis with partial respiratory compensation.

Key Concept

Clients with acute renal failure or missed dialysis develop high anion gap metabolic acidosis; the body compensates by hyperventilating (Kussmaul respirations) to lower PaCO2.
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Topics

Physiological Adaptation

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