A client's ABG report indicates PH is 7.52, PCO₂ is 30 mmHg and HCO₃ is 24 mEq/L. What does the nurse identify as a possible cause for this result?

Appeared in: SCTIMST Staff Nurse - 2016

Explanation

The client's ABG values (high pH, low PCO₂, normal HCO₃) are classic indicators of uncompensated respiratory alkalosis.
Excessive mechanical ventilation is a common cause of iatrogenic (medically-induced) hyperventilation.
Hyperventilation leads to an excessive loss of carbon dioxide (an acid), which raises the blood pH, resulting in respiratory alkalosis.
The ventilator settings, such as a high respiratory rate or tidal volume, are likely causing the client to blow off too much CO₂.

Option A: Airway obstruction impairs ventilation, leading to CO₂ retention (hypercapnia) and causing respiratory acidosis (low pH, high PCO₂), which is the opposite of the client's condition.
Option B: Inadequate nutrition or starvation can lead to the breakdown of fats for energy, producing ketones and causing metabolic acidosis (low pH, low HCO₃).
Option C: Prolonged gastric suction removes large amounts of stomach acid (HCl). The loss of acid leads to an excess of bicarbonate, causing metabolic alkalosis (high pH, high HCO₃).

Clinical Relevance

Nursing practice connection: Knowing ABG Interpretation and Causes of Respiratory Alkalosis helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
A nurse's primary responsibility is to recognize abnormal ABG values, identify the potential cause, and notify the healthcare provider promptly.
For a patient on a ventilator, recognizing respiratory alkalosis is critical. The nurse should assess the patient for signs of anxiety or pain (which can cause hyperventilation) and verify that the ventilator settings match the prescribed orders.
The nurse should anticipate orders to decrease the ventilator's respiratory rate or tidal volume to allow CO₂ levels to return to normal.

How to Approach the Question

First, analyze the pH. A value of 7.52 is above the normal 7.45, indicating alkalosis.
Next, determine if the cause is respiratory or metabolic. Look at the PCO₂ (respiratory) and HCO₃ (metabolic). The ROME mnemonic (Respiratory Opposite, Metabolic Equal) can be helpful.
In this case, the pH is high (alkalosis) and the PCO₂ (30 mmHg) is low (opposite direction). This points to a respiratory cause.
Check the HCO₃ to see if compensation has occurred. The HCO₃ (24 mEq/L) is normal, so the condition is uncompensated.
The diagnosis is Uncompensated Respiratory Alkalosis. Now, evaluate the options to find the one that causes hyperventilation and loss of CO₂.
Eliminate options that cause other imbalances: airway obstruction (respiratory acidosis), gastric suction (metabolic alkalosis), and poor nutrition (metabolic acidosis). This leaves excessive mechanical ventilation as the correct cause.

Concept Tested & Keywords

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E6 Nursing Fundamentals Potter Perry 12e Part 5 p. 56-58

E6 Medicine Harrison 22e Part 1 p. 417-419

E6 Textbook of Biochemistry for medical StudentsDM Vasudevan Part 2 — Subpart A (pp 1-239 of 478) p. 82-84

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