UBP 4.6 (Short Form): Pediatrics – Pyloric Stenosis

Question 1

What is the likely diagnosis for this neonate? How do you confirm this?

(A 4 kg female infant, delivered 13 days ago at 35 weeks of gestation is scheduled for surgery. The neonate has a 2-day history of nonbilious projectile vomiting and appears lethargic. There is a small abdominal mass 3 cm below the right costal margin. Her vital signs are as follows: BP = 74/48, HR = 113, RR = 31, T = 37 C, Hct = 51.)

Answer 1

The nonbilious projectile vomiting combined with the small abdominal mass below the right costal margin is consistent with – pyloric stenosis.

The baby’s lethargy would be consistent with the presence of a metabolic derangement associated with pyloric stenosis, namely, a –

hypokalemic, hypochloremic, hyponatremic metabolic alkalosis.

Ultrasonography or upper gastrointestinal x-rays with barium could be used to confirm the diagnosis.

Question 2

Would you proceed with surgery?

(A 4 kg female infant, delivered 13 days ago at 35 weeks of gestation is scheduled for surgery. The neonate has a 2-day history of nonbilious projectile vomiting and appears lethargic. There is a small abdominal mass 3 cm below the right costal margin. Her vital signs are as follows: BP = 74/48, HR = 113, RR = 31, T = 37 C, Hct = 51.)

Answer 2

Since the lethargy of the baby is suggestive of an electrolyte and/or metabolic derangement,

I would NOT immediatley proceed with surgery.

While pyloric stenosis can be a medical emergency, it is not a surgical emergency and surgical correction should be postponed until the infant appears clinically hydrated, has good urine output, and all electrolyte and metabolic derangements are corrected.

Specifically, I would like to see –

• a pH of 7.3-7.5,
• a sodium level of at least 130 mEq/L,
• a potassium level of at least 3 mEq/L,
• a chloride level of at least 85 mEq/L,
• a bicarbonate level less than 30 mmol/L, and
• urine output of at least 1-2 ml/kg/hr.

Question 3

What electrolyte abnormalities would you expect to see in this patient?

(A 4 kg female infant, delivered 13 days ago at 35 weeks of gestation is scheduled for surgery. The neonate has a 2-day history of nonbilious projectile vomiting and appears lethargic. There is a small abdominal mass 3 cm below the right costal margin. Her vital signs are as follows: BP = 74/48, HR = 113, RR = 31, T = 37 C, Hct = 51.)

Answer 3

Since pyloric stenosis results in vomiting of stomach contents,

which are high in sodium, potassium, chloride, and hydrogen ions,

I would expect to see a hypokalemic, hypochloremic, hyponatremic metabolic alkalosis.

I would also expect the kidneys compensatory response to alkalosis to result in a lower bicarbonate level (bicarbonate is excreted).

Question 4

Why is rehydration important in correcting the metabolic alkalosis?

(A 4 kg female infant, delivered 13 days ago at 35 weeks of gestation is scheduled for surgery. The neonate has a 2-day history of nonbilious projectile vomiting and appears lethargic. There is a small abdominal mass 3 cm below the right costal margin. Her vital signs are as follows: BP = 74/48, HR = 113, RR = 31, T = 37 C, Hct = 51.)

Answer 4

Rehydration with a sodium chloride solution supplemented with potassium is important because dehydration, and the sodium loss from vomiting, inteferes with the kidney’s compensatory mechanism for metabolic alkalosis.

Initially, the kidneys excrete bicarbonate to compensate for the metabolic alkalosis.

However, as dehydration and hyponatremia worsen, the kidneys must conserve sodium.

The conservation of sodium results in reabsorption of bicarbonate, further excretion of hydrogen, and increased bicarbonate formation.

Therefore, the renal compensatory mechanisms for dehydration lead to worsening metabolic alkalosis, making hydration an important initial step in treatment.

Question 5

What fluids would you choose for hydration during medical optimization?

(A 4 kg female infant, delivered 13 days ago at 35 weeks of gestation is scheduled for surgery. The neonate has a 2-day history of nonbilious projectile vomiting and appears lethargic. There is a small abdominal mass 3 cm below the right costal margin. Her vital signs are as follows: BP = 74/48, HR = 113, RR = 31, T = 37 C, Hct = 51.)

Answer 5

I would use normal saline to replace volume and electrolyte deficits, and,

after urine output is established, I would supplement with potassium.

If the infant’s blood sugar was low, I would consider using a glucose containing solution.

Given the likely metabolic alkalosis, lactated ringers should probably be avoided since lactate is converted to bicarbonate.

Question 6

How would you evaluate this neonate’s volume status?

(A 4 kg female infant, delivered 13 days ago at 35 weeks of gestation is scheduled for surgery. The neonate has a 2-day history of nonbilious projectile vomiting and appears lethargic. There is a small abdominal mass 3 cm below the right costal margin. Her vital signs are as follows: BP = 74/48, HR = 113, RR = 31, T = 37 C, Hct = 51.)

Answer 6

I would evaluate the patient carefully for physical signs that aid in estimating the degree of dehydration such as sunken fontanelles, skin turgor, capillary refill, heart rate, blood pressure, and mental status.

I would also ask the mother about the frequency and volume of vomiting and wet diapers.

Depending on my findings, I would start with a fluid bolus of 10-20 ml/kg of normal saline and then titrate to urine output and normalization of hemodynamic variables.

Question 7

Is this a normal hematocrit for a newborn?

(A 4 kg female infant, delivered 13 days ago at 35 weeks of gestation is scheduled for surgery. The neonate has a 2-day history of nonbilious projectile vomiting and appears lethargic. There is a small abdominal mass 3 cm below the right costal margin. Her vital signs are as follows: BP = 74/48, HR = 113, RR = 31, T = 37 C, Hct = 51.)

Answer 7

This hematocrit may be high normal for a two-week old baby as term neonates usually have a hematocrit around 55%, which then gradually declines to around 30% at 3 months of age.

This patient’s high normal hematocrit is most likely due to the dehydration that accompanies pyloric stenosis.