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Difficulty: HardPhysiological Adaptation

A client is admitted to the intensive care unit with urosepsis. During the initial assessment, the client is restless with a temperature of 38.9°C (102°F), a heart rate of 115/min, a respiratory rate of 30/min, and a blood pressure of 118/68 mm Hg. Which arterial blood gas (ABG) result should the nurse anticipate as the most likely early physiological adaptation in this client?

  1. pH 7.50, PaCO2 28 mm Hg, HCO3- 24 mEq/LAnswer
  2. B
    pH 7.31, PaCO2 36 mm Hg, HCO3- 15 mEq/L
  3. C
    pH 7.28, PaCO2 54 mm Hg, HCO3- 25 mEq/L
  4. D
    pH 7.48, PaCO2 42 mm Hg, HCO3- 31 mEq/L

Answer

The ABG result showing pH 7.50, PaCO2 28 mm Hg, HCO3- 24 mEq/L.
The correct answer reflects uncompensated respiratory alkalosis. In the early, hyperdynamic phase of sepsis, systemic inflammation and fever stimulate the respiratory center, leading to tachypnea (in this case, 30 breaths/min). This hyperventilation causes excessive exhalation of carbon dioxide (CO2). Because CO2 acts as an acid in the blood, its depletion leads to an elevated pH (alkalosis). The bicarbonate (HCO3-) remains normal initially because renal compensation takes days to occur.

Step-by-Step Solution

1
Analyze the client's vital signs and clinical presentation.
The client has urosepsis and is exhibiting signs of early systemic inflammatory response: restlessness, fever, tachycardia, and tachypnea (respiratory rate 30/min), with a stable blood pressure.
Identifying the clinical phase of sepsis determines the expected physiological responses.
2
Determine the physiological consequence of the client's tachypnea.
An elevated respiratory rate causes excessive elimination of carbon dioxide (CO2) from the lungs.
CO2 acts as an acid in the blood; losing it rapidly shifts the blood pH toward alkalosis.
3
Correlate the physiological change with expected ABG values.
The expected ABG pattern is uncompensated respiratory alkalosis, characterized by an elevated pH (>7.45), a decreased PaCO2 (<35 mm Hg), and a normal HCO3- level (22-26 mEq/L).
This matches the body's initial compensatory response before severe tissue hypoperfusion causes cellular anaerobic metabolism and lactic acidosis.

Key Concept

Early sepsis typically presents with hyperventilation, leading to respiratory alkalosis. Metabolic (lactic) acidosis develops later as tissue perfusion decreases.
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Physiological Adaptation

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