Study guide
Pediatrics on Step 2 CK spans neonatal care, common acute childhood illnesses, congenital conditions, and developmental/preventive screening. This chapter emphasizes recognizing time-sensitive neonatal conditions (hyperbilirubinemia, pyloric stenosis), applying current guideline-based thresholds for treatment and prevention, and correctly sequencing developmental and immunization screening at specific well-child visits.
Neonatal Hyperbilirubinemia and Phototherapy
Neonatal jaundice is common and requires distinguishing physiologic jaundice from pathologic causes (hemolytic disease, sepsis, biliary atresia) based on timing (jaundice in the first 24 hours of life is always pathologic and warrants urgent workup) and bilirubin trajectory. Management decisions for phototherapy and exchange transfusion are guided by nomograms that plot total serum bilirubin against the infant's age in hours and risk factors (gestational age, presence of hemolysis, other neurotoxicity risk factors), per the 2022 AAP guideline, rather than a single fixed bilirubin number applying to all infants. This means the same bilirubin level may warrant treatment in a preterm or hemolytic infant but only observation in a healthy term infant at a later postnatal hour. Vignettes test correctly using the infant's risk category and age in hours to decide whether phototherapy is indicated, and recognizing red flags (very early onset jaundice, rapidly rising bilirubin, direct/conjugated hyperbilirubinemia) that suggest a pathologic cause requiring further workup beyond simple phototherapy. Kernicterus (bilirubin-induced neurologic dysfunction) is the feared complication being prevented, which is why age-and-risk-adjusted thresholds matter more than an absolute cutoff.
Hypertrophic Pyloric Stenosis
Hypertrophic pyloric stenosis classically presents in an infant around 2-8 weeks of age with progressive, non-bilious, projectile vomiting after feeds, persistent hunger after vomiting, and a palpable 'olive-shaped' mass, typically in the right upper quadrant/epigastrium, on exam; ultrasound showing a thickened and elongated pylorus confirms the diagnosis. The critical teaching point tested on Step 2 CK is that pyloric stenosis is a medical emergency requiring stabilization before it is a surgical one: the vomiting causes a hypochloremic, hypokalemic metabolic alkalosis from loss of gastric acid and volume depletion, and this electrolyte and fluid derangement must be corrected with IV fluid resuscitation and electrolyte repletion before proceeding to surgery (pyloromyotomy). Operating on a dehydrated, alkalotic infant risks anesthesia complications including post-operative apnea from the alkalosis suppressing respiratory drive. Once the infant is adequately resuscitated and electrolytes normalized, pyloromyotomy is curative. Vignettes test recognizing the classic presentation and lab pattern, and specifically choosing IV fluid/electrolyte correction as the immediate next step rather than proceeding directly to surgery.
Bronchiolitis and RSV Prevention
Bronchiolitis, most commonly caused by respiratory syncytial virus (RSV), presents in infants and young children with upper respiratory symptoms progressing to wheezing, tachypnea, and increased work of breathing, typically peaking around day 3-5 of illness. Management is largely supportive: nasal suctioning, ensuring adequate hydration and oxygenation, with supplemental oxygen for hypoxemia; bronchodilators, corticosteroids, and antibiotics are not routinely recommended since bronchiolitis is viral and does not reliably respond to bronchodilator therapy despite the wheezing. Hospitalization is reserved for infants with significant respiratory distress, hypoxemia, inability to maintain hydration, or apnea, with particular caution in young infants and those with underlying cardiopulmonary disease or prematurity. RSV prevention has evolved with nirsevimab, a long-acting monoclonal antibody, now recommended for infants entering their first RSV season (particularly when the mother did not receive the maternal RSVpreF vaccine during pregnancy) to reduce the risk of severe RSV lower respiratory tract disease, representing a shift from the older palivizumab prophylaxis, which required monthly dosing and has been phased out. Step 2 CK tests recognizing bronchiolitis as a supportive-care diagnosis (avoiding the distractor of reflexively prescribing bronchodilators or antibiotics) and knowing which infants qualify for RSV immunoprophylaxis.
Developmental Screening and Adolescent Preventive Care
Developmental surveillance is built into well-child visits, and universal autism-specific screening is recommended at the 18-month (and again at the 24-month) well-child visit using a validated standardized screening tool such as the M-CHAT-R/F, regardless of whether parents or the pediatrician have specific concerns, reflecting a shift toward universal rather than concern-triggered screening. Positive screens prompt referral for formal developmental/autism evaluation and early intervention services, since early intervention improves outcomes. Separately, adolescent preventive care at the 11-12-year well visit includes a bundle of routine immunizations: the first dose of the HPV vaccine series (ideally started at 11-12 years for maximal effectiveness before likely exposure), a meningococcal conjugate (MenACWY) vaccine dose, and a Tdap booster. Step 2 CK tests knowing which vaccines are due at this specific visit and the rationale for HPV vaccine timing (started well before the onset of sexual activity to maximize immunogenicity and prevent HPV-related cancers). These preventive care vignettes reward precise recall of the specific ages tied to each screening or immunization intervention rather than general familiarity with the guideline's existence.
Key terms
- Bilirubin nomogram (age-in-hours based)
- — A risk-stratified chart used to decide phototherapy or exchange transfusion thresholds for neonatal hyperbilirubinemia based on the infant's age in hours and risk factors, not a single fixed number.
- Kernicterus
- — Bilirubin-induced neurologic damage, the feared complication that age/risk-adjusted phototherapy thresholds are designed to prevent.
- Hypochloremic, hypokalemic metabolic alkalosis
- — The classic electrolyte derangement in pyloric stenosis from prolonged vomiting of gastric contents, which must be corrected before surgery.
- Pyloromyotomy
- — The curative surgical procedure for hypertrophic pyloric stenosis, performed only after fluid and electrolyte resuscitation.
- Nirsevimab
- — A long-acting monoclonal antibody given to infants for passive RSV immunoprophylaxis, reducing risk of severe RSV lower respiratory tract disease; it has replaced monthly palivizumab as the standard approach.
- Universal autism screening
- — Standardized autism-specific screening (e.g., M-CHAT-R/F) recommended for all children at the 18-month (and 24-month) well-child visit, regardless of parental concern.
- 11-12-year adolescent well visit vaccines
- — Routine bundle including HPV vaccine series initiation, meningococcal conjugate (MenACWY) vaccine, and Tdap booster.
- Non-bilious projectile vomiting
- — The classic vomiting pattern of hypertrophic pyloric stenosis, distinguishing it from bilious vomiting concerning for intestinal obstruction/malrotation.
Exam tips
- In pyloric stenosis vignettes, choose IV fluid and electrolyte correction as the immediate next step, not the surgery, even though pyloromyotomy is curative.
- For neonatal jaundice, jaundice appearing in the first 24 hours of life is never physiologic — treat it as pathologic and investigate immediately.
- Don't select bronchodilators or antibiotics for classic bronchiolitis — supportive care (suction, oxygen, hydration) is the tested answer.
- Know that autism screening is universal at 18 months regardless of parental concern — a stem saying 'parents have no concerns' should not change your answer.
- Match the 11-12-year well visit to its specific vaccine bundle (HPV, MenACWY, Tdap) when a vignette asks what's due at that visit.
- Use bilirubin nomograms mentally as 'age in hours plus risk factors,' not a flat number — the same bilirubin level can be normal or actionable depending on the infant's age and risk category.