Pyloric Stenosis

A 3-week-old first-born male infant had projectile vomiting, which contained the ingested formula but no bile. His body weight was 2.5 kg; serum electrolytes: K⁺ 2.2 mEq per L, Cl^– 86 mEq per L; and blood pH 7.68. This infant was also noted to have a systolic murmur heard best at the second intercostal space along the left sternal border, which was assessed by a cardiologist and diagnosed as a ventricular septal defect (VSD).

A. Medical Disease and Differential Diagnosis

What is the diagnosis in this patient?
What is the differential diagnosis of pyloric stenosis?
What are the metabolic problems in this newborn secondary to his disease?
What are the adverse effects of metabolic alkalosis?
How would you treat this infant?
How would you determine fluid replacement in a newborn, and what fluids would you use?
How would you correct the metabolic alkalosis in this patient?
What causes a cardiac murmur?

B. Preoperative Evaluation and Preparation

How would you evaluate this patient preoperatively?
How would you evaluate a heart murmur?
How would you differentiate between functional versus organic murmur?
What are the types of VSD? What type of shunt do they cause?
What are the risks of surgery and anesthesia in a patient with VSD?
How would you prepare this patient rapidly for emergency surgery? Is surgical intervention an acute emergency in this case?
How would you prepare this patient for anesthesia?

C. Intraoperative Management

What induction-intubation sequence would you use?
What are the anatomic characteristics of the airway in the newborn and how do they differ from those in the adult?
How do you determine the size of an endotracheal tube in a pediatric patient?
What anesthesia system would you use and why?
What are the advantages and the disadvantages of commonly employed nonrebreathing systems?
How would you monitor this patient intraoperatively?
How does the pulse oximeter function?
What factors affect the measurement of oxygen saturation by the pulse oximeter?

D. Postoperative Management

What are the complications that can occur in the postanesthesia recovery period?
How would you treat postextubation “croup” in this infant?

A. Medical Disease and Differential Diagnosis

A.1. What is the diagnosis in this patient?

The most likely diagnosis in this patient is pyloric stenosis. The factors that favor the diagnosis are as follows:

Age—3 weeks (average age at onset; range 5 days to 5 months)
Boy child (boy-to-girl ratio = 4:1)
Projectile vomiting (characteristic)
Contents—ingested formula, no bile

The resultant biochemical abnormality in this patient is a hypokalemic, hypochloremic, metabolic alkalosis.

Pyloric stenosis occurs in 3 of 1,000 infants born in the United States; its incidence may be increasing. It is more common in Whites of Northern European ancestry, less common in Blacks, and rare in Asians. Reduced nitric oxide in pyloric tissue may contribute to the pathogenesis of pyloric stenosis.

Kliegman RM, Stanton BF, St Geme JW, et al, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier Saunders; 2015.

A.2. What is the differential diagnosis of pyloric stenosis?

Pyloric stenosis can be distinguished from other congenital anomalies that cause obstruction of the alimentary tract in the newborn. These other anomalies include chalasia of the esophagus, hiatus hernia, duodenal atresia, jejunal atresia, ileal atresia, pancreatic annulus, malrotation of the gut, intra-abdominal hernias, and Meckel’s diverticulum. Pathognomonic features of pyloric stenosis include absence of bile staining of the vomitus and visible gastric peristaltic waves on abdominal examination along with the palpable pyloric mass. The diagnosis is commonly made clinically. An “olive” is sometimes palpated in the epigastrium just to the right of the midline. The diagnosis can be confirmed by abdominal ultrasound. Occasionally, an upper gastrointestinal (GI) series with barium may be necessary.

Kliegman RM, Stanton BF, St Geme JW, et al, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier Saunders; 2015.

A.3. What are the metabolic problems in this newborn secondary to his disease?

Metabolic changes occur secondary to protracted vomiting and characteristically include a hypokalemic, hypochloremic alkalosis, as evident in this infant. Hyponatremia, although present, may not be manifested in serum value determinations because of severe dehydration. Compensatory respiratory acidosis is a frequent finding; it results from hypoventilation that may be marked and associated with periods of apnea. In severe dehydration leading to circulatory shock, the lack of adequate perfusion coupled with impaired renal and hepatic function may produce an entirely different picture of metabolic acidosis with hyperventilation, resulting in respiratory alkalosis. Therefore, depending on the severity and duration of vomiting and the type of fluid replenishment, one can encounter wide variations in arterial blood gas and electrolyte determinations. However, the most frequent findings are hypokalemia, hyponatremia, hypochloremia, and primary metabolic alkalosis with secondary respiratory acidosis. The renal response to vomiting is twofold. Initially, serum pH is maintained by the excretion of alkaline urine with sodium and potassium loss.
Then, after the depletion of these electrolytes, the kidneys secrete acidic urine (paradoxic acidosis), which exacerbates the metabolic alkalosis. These findings are summarized in Table 40.1.

TABLE 40.1 Metabolic Findings in the Newborn Secondary to Pyloric Stenosis

SEVERITY OF DEHYDRATION	ARTERIAL BLOOD GASES				SERUM ELECTROLYTES
SEVERITY OF DEHYDRATION	pH	PCO₂	CO₂	PO₂	NA	K	CL	HCO₃
Mild	↑	↑	↑	↔	↓ ↔	↓	↓↓	↑
Moderate	↑↑	↑↑	↑↑	↔	↓	↓↓	↓↓↓	↑↑
Severe	↓↓	↓	↓↓	↓	↓	↓↓	↓↓↓	↓↓
↔, no change; ↑/↓, slight change; ↑↑/↓↓, moderate change; ↑↑↑/↓↓↓, marked change.

Davis PJ, Cladis FP, Motoyama EK, eds. Smith’s Anesthesia for Infants and Children. 8th ed. Philadelphia, PA: Mosby Elsevier; 2011:750-751.

Kliegman RM, Stanton BF, St Geme JW, et al, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier Saunders; 2015.

A.4. What are the adverse effects of metabolic alkalosis?

An increase in pH results in shifting of the oxygen-dissociation curve to the left, thereby binding more oxygen to the hemoglobin and unloading less oxygen at the tissue level. This phenomenon assumes even more importance in newborns because at 3 weeks they still have up to 70% fetal hemoglobin with an already low value of P50 (i.e., 20 to 22 mm Hg).
Respiratory compensation is affected by hypoventilation with increased potential for atelectasis as well as periods of apnea
Decrease in ionized calcium
Increased potential for seizures

Kliegman RM, Stanton BF, St Geme JW, et al, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier Saunders; 2015.

A.5. How would you treat this infant?

Medical management of this infant with pyloric stenosis is acutely urgent. The principles of management can be grouped under the following three categories: supportive therapy, to stabilize the patient; diagnostic tests, to confirm the diagnosis and to monitor therapy; and surgery as the corrective therapy.

Supportive Therapy

Circulatory support
Correction of electrolyte imbalance
Prevention of aspiration

Fluids

The infant with pyloric stenosis is hypovolemic and dehydrated secondary to persistent vomiting. Dehydration severity can vary from mild hypovolemia to circulatory shock. The following parameters are good indicators of dehydration severity:

Physical appearance—skin turgor, parched mucous membranes, sunken fontanels, sunken eyeballs
Blood pressure—decreased
Pulse—increased
Urine output—decreased
Weight (birth and present) and weight loss

Quantitative assessment of these parameters gives a fair estimate of the amount of total body fluid depletion. A wide-bore intravenous cannula should be placed and an infusion started immediately to correct the deficits and provide maintenance fluids.

Electrolytes

The patient is alkalotic, hypokalemic, hypochloremic, and hyponatremic and must be provided with necessary ions to replenish the deficit. Albumin or Ringer’s lactate may be used to treat the shock first. Next, the deficit should be corrected, 0.45% to 0.9% saline in 5% to 10% dextrose. Potassium (usually 40 mEq per L) must be added to this to correct hypokalemia and aid in the correction of alkalosis. However, potassium infusion should be withheld until satisfactory renal function is established. Fluid therapy should be continued until the infant is rehydrated and serum bicarbonate concentration is less than 30 mEq per dL, which implies that the alkalosis has been corrected.

Prevention of Aspiration

A nasogastric tube should be inserted to thoroughly empty the stomach, and the upper airway reflexes should be preserved.

Diagnostic Tests

To assess the severity of fluid and electrolyte derangement and to monitor therapy, the following should be evaluated: complete blood count, serum electrolytes, blood gases, blood urea nitrogen (BUN), electrocardiogram (ECG) (for marked hypokalemia).
To confirm the diagnosis: barium swallow, ultrasound imaging

Surgery

Pyloromyotomy is the definitive treatment for these infants. Ramstedt pyloromyotomy through a right upper quadrant transverse incision has been the traditional treatment for hypertrophic pyloric stenosis. Recently, laparoscopic and circumumbilical approaches have been introduced as alternative methods to improve cosmesis, but concerns about greater operative times, costs, and complications remain. Surgery should be carried out early but only after the patient has been stabilized satisfactorily.

Blatnik JA, Ponsky TA. Advances in minimally invasive surgery in pediatrics. Curr Gastroenterol Rep. 2010;12(3):211-214.

Kliegman RM, Stanton BF, St Geme JW, et al, eds. Nelson Textbook of Pediatrics. 20th ed. Philadelphia, PA: Elsevier Saunders; 2015.

A.6. How would you determine fluid replacement in a newborn, and what fluids would you use?

The general principles of fluid therapy are based on fluid maintenance, correction of deficits, and replacement of losses.

Maintenance Fluids

In the newborn, maintenance fluids are as follows:

First 48 hours of life—75 mL/kg/day or 3 mL/kg/hr
2 days to 1 month—150 mL/kg/day or 6 mL/kg/hr
1 month onward (up to 10 kg)—100 mL/kg/day or 4 mL/kg/hr

Estimation of the degree of dehydration in a newborn is shown in Table 40.2.

The maintenance fluids take into account the fluid losses occurring normally through the kidney, bowel, skin, and lungs. At birth, the kidney is still undergoing maturation, and what may be called “a glomerular imbalance” exists. What it implies is that some mature glomeruli may be connected to the immature tubules and vice versa. Hence, the kidney is functionally limited at birth but undergoes rapid maturation during the first week of life.

Electrolytes

The newborn is an obligate sodium loser as well as a poor tolerator of excessive sodium overload. The maintenance electrolytes are as follows: