The patient in the gastroenterology ward is on nasogastric tube with continuous low-pressure suction. The acid-base disorder you anticipate in this setting is:

Appeared in: GMCH - 2016

Explanation

Continuous nasogastric (NG) suction removes gastric contents, which are highly acidic due to hydrochloric acid (HCl).
The removal of acid (hydrogen ions, H⁺) from the body leads to a relative excess of bicarbonate (HCO₃⁻), which is a base.
This shift increases the blood's pH, causing a state of metabolic alkalosis.
This condition is often described as hypochloremic, hypokalemic metabolic alkalosis because chloride and potassium are also lost along with the gastric acid.

Option A: Metabolic acidosis results from a gain of acid or loss of base. NG suction causes a loss of acid.
Option C: Respiratory acidosis is caused by hypoventilation and CO₂ retention, a pulmonary issue, not a gastrointestinal one.
Option D: Respiratory alkalosis is caused by hyperventilation and excessive loss of CO₂, a pulmonary issue.

Clinical Relevance

Nursing practice connection: Use the key finding related to Acid-base imbalance caused by gastrointestinal fluid loss to guide bedside assessment, documentation, and the next nursing action.
Nurses caring for patients with NG suction must diligently monitor for signs and symptoms of metabolic alkalosis, which include confusion, muscle twitching, tingling in extremities, and potentially cardiac arrhythmias.
It is crucial to monitor the patient's serum electrolyte levels (especially potassium and chloride) and arterial blood gas (ABG) results to detect and manage the imbalance promptly.
Nursing interventions include administering IV fluids and electrolyte replacements as prescribed to correct the deficit and prevent complications.

How to Approach the Question

First, identify the key procedure in the question: 'nasogastric tube with continuous low-pressure suction.'
Next, recall the nature of the fluid being removed. Gastric fluid from the stomach is highly acidic due to hydrochloric acid (HCl).
Analyze the effect of removing this fluid. Removing a large amount of acid from the body will cause the blood's pH to rise, making it more alkaline (basic).
Determine if the cause is metabolic or respiratory. Since the origin of the problem is the gastrointestinal system (a metabolic organ system) and not the lungs, the disorder is metabolic.
Combine these two deductions: a metabolic cause leading to an alkaline state is 'metabolic alkalosis.'
Finally, review the options and select the one that matches your conclusion.

Concept Tested & Keywords

Concept Tested: Acid-base imbalance caused by gastrointestinal fluid loss.
Stem keywords: nasogastric tube, continuous low-pressure suction, acid-base disorder, gastroenterology
Lead-in keywords: anticipate
Clinical cues: The clinical intervention of continuous nasogastric suction is the key detail pointing to the specific type of fluid and electrolyte loss.

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

E6 Nelson Textbook of Pediatrics(2024) — Volume 1 p. 564-566

Practise the full GMCH - 2016

Attempt every question from this paper in a timed mock, then review the full solution for each one.