A 4-month-old infant is brought to the emergency department by parents who report that the child has been vomiting forcefully after feedings for the past week. What is the most important initial assessment the nurse should perform?
1Measure the infant's head circumference
2Check the infant's temperature and heart rate
3Assess the infant's bowel sounds in all four quadrants
4Evaluate the infant's hydration status and skin turgor✓ 정답
해설
Evaluating hydration status is the priority for an infant with persistent vomiting, as dehydration can develop rapidly and become life-threatening. Other assessments like head circumference or bowel sounds are less urgent.
The infant in this scenario is presenting with a classic history for infantile hypertrophic pyloric stenosis (IHPS), an acquired condition where the pyloric muscle undergoes progressive hypertrophy, leading to gastric outlet obstruction. The hallmark symptom is projectile, non-bilious vomiting that typically begins around 3 to 6 weeks of age but can present up to 4 months. Because the obstruction is proximal to the duodenum, bile is not present in the emesis. As the obstruction worsens, the infant cannot retain gastric contents, including hydrochloric acid, leading to a predictable sequence of fluid and electrolyte losses.
Pathophysiology and Rationale for Priority Assessment
The most immediate threat to life in a patient with prolonged, forceful vomiting is hypovolemic shock secondary to severe dehydration. In IHPS, the persistent loss of gastric secretions results in a unique metabolic disturbance: hypochloremic, hypokalemic metabolic alkalosis. The stomach secretes hydrochloric acid (HCl); when this is lost through vomiting, hydrogen ions (H⁺) and chloride ions (Cl⁻) are depleted. The kidneys initially attempt to compensate for the alkalosis by excreting bicarbonate, but as volume depletion worsens, the renal tubules prioritize sodium reabsorption in exchange for potassium and hydrogen ions, a process driven by aldosterone. This paradoxical aciduria worsens the hypokalemia and perpetuates the alkalosis.
Therefore, the most important initial nursing assessment is to determine the severity of the fluid volume deficit. Evaluating hydration status and skin turgor provides immediate, non-invasive data on the infant's hemodynamic stability. Key findings in significant dehydration include a depressed anterior fontanelle, absence of tears when crying, dry mucous membranes, prolonged capillary refill time, and the classic "tenting" of skin when turgor is assessed over the abdomen or thigh. These clinical signs guide the urgency of fluid resuscitation, which is the first step in stabilizing the infant before any surgical intervention is considered [1].
Analysis of Incorrect Options
- Option 1: Measure the infant's head circumference. While a baseline head circumference is a routine part of any infant assessment, it is not the priority in the context of acute projectile vomiting. Increased head circumference would be more indicative of increased intracranial pressure, which can cause vomiting, but the forceful, post-prandial nature of the vomiting here strongly points to a gastrointestinal obstruction rather than a neurological etiology.
- Option 2: Check the infant's temperature and heart rate. Vital signs are a critical component of the assessment. However, the question asks for the most important initial assessment. Tachycardia is a compensatory mechanism and a late sign of hypovolemia. Directly assessing skin turgor, mucous membranes, and fontanelles gives a more direct picture of the fluid deficit that is driving the heart rate change. The assessment of hydration status encompasses the interpretation of vital signs but requires a hands-on evaluation of the physical markers of dehydration.
- Option 3: Assess the infant's bowel sounds in all four quadrants. Auscultation of bowel sounds is a standard part of an abdominal assessment. In IHPS, bowel sounds may initially be hyperactive as the stomach attempts to overcome the obstruction, but this finding is neither specific nor the most critical indicator of the patient's immediate physiologic stability. The life-threatening consequence of the obstruction is the fluid and electrolyte loss, not the alteration in peristalsis itself.
Clinical Reasoning and Diagnostic Correlation
The nursing priority follows the ABCs (Airway, Breathing, Circulation) and the concept of "treat the patient, not the diagnosis." While the history is highly suggestive of IHPS, the nurse's first action is to gauge the impact of the vomiting on the infant's circulatory volume. A severely dehydrated infant may present with lethargy, cool extremities, and a delayed capillary refill, indicating that compensatory mechanisms are failing. This assessment data is essential for the healthcare team to determine the type and rate of intravenous fluid resuscitation needed to correct the hypovolemia and electrolyte imbalances before a diagnostic ultrasound is performed. Ultrasonography is the diagnostic modality of choice for confirming IHPS by measuring pyloric muscle thickness and canal length, but imaging is deferred until the patient is hemodynamically stable [1].
References (research sources)
[1]
Hypertrophic Pyloric Stenosis in a Four-Week-Old Infant: Radiological Diagnosis and Pitfalls.Research articlePokhrel B, Bhatta A, Basnet A, Pokhrel N, Regmi D. (2025) · DOI: 10.7759/cureus.98606
Clinical Priority: Infant with Projectile Vomiting
An infant presenting with a one-week history of forceful, postprandial vomiting is a classic presentation for infantile hypertrophic pyloric stenosis (IHPS) until proven otherwise. The most immediate threat to life is not the anatomical obstruction itself, but the resulting severe dehydration and electrolyte derangement leading to hypovolemic shock.
Nursing Assessment Priority
Primary Survey (ABCs): The initial assessment must focus on circulatory status. Evaluate hydration status by checking skin turgor (e.g., on the abdomen or thigh), moisture of mucous membranes, presence of tears, and anterior fontanelle status. Capillary refill time and heart rate are critical adjuncts.
Recognize the Electrolyte Pattern: Persistent vomiting of gastric contents leads to loss of hydrochloric acid. This results in a hypochloremic, hypokalemic metabolic alkalosis. The nurse must anticipate this specific imbalance when reviewing lab results.
Secondary Assessment: After stabilizing the immediate threat, a focused abdominal assessment can be performed. An "olive-shaped" mass may be palpable in the right upper quadrant, and visible gastric peristaltic waves may be observed moving from left to right across the epigastrium just before emesis.
Clinical Management Guide
Fluid Resuscitation: Medical management takes priority over immediate surgical intervention. The infant must be hemodynamically stable with corrected electrolyte imbalances before undergoing pyloromyotomy. This typically involves intravenous normal saline boluses followed by maintenance fluids with potassium supplementation once urine output is established.
Preoperative Care: Maintain NPO status and place the infant in a prone or right-side-lying position with the head of the bed elevated to facilitate gastric emptying and reduce aspiration risk. Continuously monitor intake and output, daily weights, and vital signs.
Postoperative Feeding: After a pyloromyotomy, feedings are typically resumed within 4-6 hours. Start with small volumes of clear liquids (e.g., Pedialyte) and advance to full-strength formula or breast milk as tolerated. Parents should be educated that some post-operative vomiting can be normal initially.
Infantile Hypertrophic Pyloric Stenosis (IHPS) — An acquired condition causing progressive hypertrophy of the pyloric muscle, leading to gastric outlet obstruction and projectile non-bilious vomiting in infants typically 3-6 weeks old.
Hypochloremic Hypokalemic Metabolic Alkalosis — A classic electrolyte imbalance in IHPS caused by loss of hydrochloric acid from vomiting, leading to depleted chloride and potassium levels and elevated blood pH.
Skin Turgor — A measure of skin elasticity used to assess hydration status; tenting of the skin indicates moderate to severe dehydration.
Projectile Vomiting — Forceful expulsion of stomach contents, a hallmark symptom of pyloric stenosis as the hypertrophied muscle obstructs the passage of food.