A nurse is caring for an infant who has intractable vomiting. The MOST important likely complication is:

Appeared in: BHU NO-2019

Explanation

Intractable vomiting causes the loss of large amounts of gastric fluid, which is rich in hydrochloric acid (HCl).
The loss of hydrogen ions (H⁺), an acid, leads to a relative excess of bicarbonate (HCO₃⁻), a base, in the bloodstream.
This imbalance raises the body's pH, resulting in metabolic alkalosis.
Volume depletion from vomiting also stimulates the kidneys to retain sodium and bicarbonate, which further maintains the alkalotic state.

Option A: Acidosis is incorrect. It is caused by a loss of bicarbonate (a base) or an accumulation of acid from other sources, not the loss of gastric acid.
Option B: Hyperkalemia (high potassium) is incorrect. Vomiting leads to the loss of potassium both in the vomitus and through increased renal excretion due to dehydration, causing hypokalemia (low potassium).
Option C: Hypernatremia (high sodium) is incorrect. Vomiting causes the loss of both water and sodium. This typically leads to hyponatremia (low sodium) or isonatremic (normal sodium) dehydration.

Clinical Relevance

Nursing practice connection: Use the key finding related to Acid-Base Imbalances: Metabolic Alkalosis to guide bedside assessment, documentation, and the next nursing action.
Nurses must recognize that intractable vomiting in an infant is a serious condition that requires prompt intervention to prevent severe dehydration and life-threatening electrolyte and acid-base imbalances.
Key nursing assessments include monitoring vital signs for tachycardia (an early sign of dehydration), checking skin turgor and fontanelles, and strictly measuring urine output (less than 1 mL/kg/hr is a red flag).
What if? If the question stated the infant had pyloric stenosis, the answer would still be metabolic alkalosis. Pyloric stenosis is a classic cause of non-bilious, projectile vomiting in infants, leading to the same loss of gastric acid.

How to Approach the Question

First, identify the core physiological process described in the question: intractable vomiting in an infant.
Next, consider the composition of the fluid being lost. Vomitus contains gastric fluid, which is primarily hydrochloric acid (HCl).
Analyze the effect of losing this fluid on the body's acid-base balance. Losing a strong acid (H⁺) will make the blood more basic (alkaline).
This directly points to alkalosis as the correct answer.
Briefly evaluate the other options. Vomiting also causes loss of potassium and sodium, so 'hyper-' states (hyperkalemia, hypernatremia) are unlikely. Acidosis is the opposite of alkalosis and is associated with diarrhea.

Concept Tested & Keywords

Concept Tested: Acid-Base Imbalances: Metabolic Alkalosis
Stem keywords: infant, intractable vomiting, complication
Lead-in keywords: MOST important, likely
Clinical cues: Intractable vomiting is a key cue indicating significant loss of gastric contents.

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E6 Nelson Textbook of Pediatrics(2024) — Volume 1 pp. 563-565, 576-578

Practise the full BHU NO-2019

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