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Difficulty: Very hardPhysiological Adaptation

An adolescent client is brought to the emergency department after ingesting a toxic amount of acetylsalicylic acid (aspirin) 6 hours ago. The client is confused, diaphoretic, and reports tinnitus. Vital signs are: heart rate 124 beats/min, respiratory rate 34 breaths/min and deep, and blood pressure 102/64 mm Hg. Arterial blood gas (ABG) analysis reveals: pH 7.31, PaCO2 24 mm Hg, HCO3 12 mEq/L, and PaO2 96 mm Hg. Which physiological interpretation and corresponding priority action is most appropriate for this client?

  1. Partially compensated metabolic acidosis; prepare to administer an intravenous sodium bicarbonate infusion.Answer
  2. B
    Uncompensated respiratory alkalosis; initiate rebreathing techniques using a paper bag to increase carbon dioxide retention.
  3. C
    Partially compensated respiratory acidosis; prepare for immediate endotracheal intubation to support failing respiratory drive.
  4. D
    Progressive hypovolemic shock with lactic acidosis; administer a rapid isotonic intravenous fluid bolus.

Answer

The correct interpretation is partially compensated metabolic acidosis, and the priority action is to prepare an intravenous sodium bicarbonate infusion.
The ABG results demonstrate a partially compensated metabolic acidosis. The pH is acidic (less than 7.35), which matches the low bicarbonate level (metabolic origin). The low carbon dioxide level indicates the respiratory system is attempting to compensate by hyperventilating. In acetylsalicylic acid (aspirin) toxicity, the priority intervention is alkalinizing the blood and urine with intravenous sodium bicarbonate. This treatment converts the toxic salicylate into an ionized form that cannot cross back into the tissues, trapping it in the renal tubules and rapidly accelerating its excretion from the body.

Step-by-Step Solution

1
Analyze the arterial blood gas (ABG) pH value to determine the primary acid-base status.
The pH is 7.31, which is below the normal range of 7.35-7.45, indicating acidemia.
Establishing the pH direction is the first step in identifying the primary physiological disturbance.
2
Evaluate the PaCO2 and HCO3 values to determine the origin of the acidosis.
The HCO3 is low (12 mEq/L), which matches the acidic pH, confirming a metabolic origin. The PaCO2 is also low (24 mm Hg).
Matching the abnormal parameter to the pH direction identifies whether the primary cause is respiratory or metabolic.
3
Determine the level of compensation based on the opposite parameter and the pH.
The low PaCO2 indicates the respiratory system is blowing off acid to compensate, but because the pH (7.31) is not yet back to normal, the condition is only partially compensated.
Assessing the opposite system reveals if physiological adaptation is occurring to restore homeostasis.
4
Identify the primary pharmacological intervention for the specific toxidrome (salicylate poisoning) causing the metabolic acidosis.
Intravenous sodium bicarbonate is required to alkalinize the urine and trap the salicylate ions for rapid renal excretion.
Treating the underlying toxicological cause is essential to reverse the severe, life-threatening metabolic derangement.

Key Concept

In severe salicylate (aspirin) toxicity, clients develop a profound high anion gap metabolic acidosis. The physiological adaptation is compensatory hyperventilation (Kussmaul respirations), and the priority pharmacological intervention is urinary alkalinization using intravenous sodium bicarbonate to trap and excrete the toxin.
Estimated Time:2m 0s
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Physiological Adaptation

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