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Difficulty: HardPhysiological Adaptation

A nurse is assessing a client admitted with a severe kidney infection and suspected urosepsis. The client is restless but oriented. Current vital signs are: blood pressure 112/64112/64 mm Hg, heart rate 118118 beats/min with bounding pulses, respiratory rate 2828 breaths/min, and temperature 39.2∘39.2^\circ C (102.6∘102.6^\circ F). The client's skin is warm and flushed. Based on this physiological presentation, which of the following arterial blood gas (ABG) results should the nurse anticipate?

  1. pH 7.487.48, PaCO2\text{PaCO}_2 3030 mm Hg, HCO3−\text{HCO}_3^- 2323 mEq/LAnswer
  2. B
    pH 7.257.25, PaCO2\text{PaCO}_2 3636 mm Hg, HCO3−\text{HCO}_3^- 1515 mEq/L
  3. C
    pH 7.317.31, PaCO2\text{PaCO}_2 5050 mm Hg, HCO3−\text{HCO}_3^- 2424 mEq/L
  4. D
    pH 7.437.43, PaCO2\text{PaCO}_2 2929 mm Hg, HCO3−\text{HCO}_3^- 1818 mEq/L

Answer

pH 7.48, PaCO2 30 mm Hg, HCO3- 23 mEq/L
The correct result shows uncompensated respiratory alkalosis. In the early (hyperdynamic) phase of septic shock, inflammatory mediators and circulating endotoxins directly stimulate the respiratory center, leading to tachypnea (hyperventilation). This causes the client to exhale excessive amounts of carbon dioxide, decreasing the partial pressure of arterial carbon dioxide (PaCO2) and increasing the pH. Because this is an acute physiological change, the kidneys have not yet had the 24 to 48 hours required to compensate, leaving the bicarbonate (HCO3-) level within the normal range.

Step-by-Step Solution

1
Analyze the client's clinical presentation to determine the specific phase of sepsis.
Warm flushed skin, bounding pulses, a normal blood pressure, and high fever indicate the early (hyperdynamic or 'warm') phase of septic shock.
In early sepsis, massive vasodilation occurs, but cardiac output increases compensatorily, maintaining blood pressure and producing warm skin.
2
Identify the primary physiological adaptation affecting the respiratory system.
The client is hyperventilating with a respiratory rate of 28 breaths/min.
Systemic inflammation and bacterial endotoxins directly stimulate the respiratory center in the medulla, causing tachypnea even before hypoxia occurs.
3
Determine the expected acid-base imbalance resulting from this respiratory pattern.
Hyperventilation causes excessive exhalation of carbon dioxide, leading to an acute decrease in PaCO2 and a rise in pH (respiratory alkalosis).
Carbon dioxide acts as an acid in the body; losing it rapidly shifts the blood pH toward alkalosis.
4
Evaluate the timeline for expected metabolic compensation.
An uncompensated state (normal HCO3-) is expected.
Renal compensation (excreting bicarbonate to lower the pH) takes 24 to 48 hours to become fully effective. An acute presentation will show normal bicarbonate levels.

Key Concept

Early Septic Shock Pathophysiology and Acid-Base Imbalances
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Topics

Physiological Adaptation

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