Nasogastric suction causes which type of acid-base imbalance?

Appeared in: NORCET 1 - 2020

Explanation

Nasogastric (NG) suction removes gastric contents, which are highly acidic due to hydrochloric acid (HCl).
The removal of acid (H+ ions) from the body leads to a relative excess of bicarbonate (a base) in the blood.
This shift results in an increase in blood pH, a condition known as metabolic alkalosis.
It is considered 'metabolic' because the primary cause is the loss of acid from the gastrointestinal system, not a change in respiratory function.

Option A: Metabolic acidosis involves a loss of base or gain of acid. NG suction causes a loss of acid, which is the opposite.
Option C: Respiratory acidosis is caused by the lungs retaining too much carbon dioxide (CO₂), a problem of ventilation, not a metabolic issue related to the GI tract.
Option D: Respiratory alkalosis is caused by the lungs eliminating too much CO₂ through hyperventilation. The cause in the question is metabolic.

Visual 1: Flowchart: Illustrating the pathway from nasogastric suction → loss of HCl → decreased H+ ions → increased blood pH → metabolic alkalosis.
Visual 2: Infographic: A summary table of the four main acid-base imbalances (Metabolic/Respiratory Acidosis/Alkalosis), including their primary causes, pH, PaCO₂, and HCO₃⁻ changes.

Clinical Relevance

Nursing practice connection: Knowing Acid-base imbalance caused by nasogastric suction helps nurses interpret findings accurately and avoid errors in routine assessment, medication administration, and patient teaching.
Nurses must monitor patients with NG suction for signs of metabolic alkalosis, such as confusion, muscle cramps, and tingling in the extremities.
It is crucial to monitor serum electrolyte levels, particularly potassium (K⁺), as hypokalemia often accompanies metabolic alkalosis.
What if? If the patient had an intestinal fistula instead of NG suction, the primary risk would shift to metabolic acidosis due to the loss of bicarbonate-rich intestinal fluid.

How to Approach the Question

First, identify the procedure in the question: Nasogastric suction.
Next, determine what substance is being removed from the body. NG suction removes contents from the stomach.
Recall the nature of stomach contents. They are highly acidic due to the presence of hydrochloric acid (HCl).
Analyze the effect of removing acid from the body. Losing acid makes the blood more alkaline (basic).
Differentiate between metabolic and respiratory causes. Since the cause is related to the gastrointestinal system (a metabolic organ system) and not the lungs, the imbalance is metabolic.
Combine these points: A metabolic process is causing an alkaline state. This leads to the correct answer: Metabolic alkalosis.

Concept Tested & Keywords

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