Emergencies in the Neonate and Young Infant

Young infants who present to the emergency department (ED) warrant timely triage and evaluation. In this patient group, nonspecific concerns — including increased sleepiness, irritability, pallor, and poor feeding — can herald serious systemic illness.

The following emergencies in neonates and infants are addressed in this section:

• The Ill or Lethargic Infant

• Fever in Young Infants

• Neonatal Herpes Simplex Virus (HSV)

• Pyloric Stenosis

The Ill or Lethargic Infant

Differential Diagnosis

The differential diagnosis for the ill-appearing infant is broad and includes pathologies originating from a multitude of organ systems. The most common cause of ill appearance in a young infant is infection, either bacterial or viral, but some less-common etiologies can also be life-threatening if left unrecognized. In this section, we cover herpes simplex virus, sepsis, and pyloric stenosis. Other diagnoses will be covered in the respective guides.

Assessment

The evaluation of the ill-appearing infant begins with rapid assessment of airway, breathing, and circulation and includes a thorough history and physical examination.

History: Key information to elicit during the history includes:

• gestational age, perinatal history (including maternal infections treated prenatally and/or intrapartum), family history of childhood diseases, events leading to presentation

• feeding, weight gain, sweating or cyanosis with feeds, repeated emesis

• fever, hypothermia, tachypnea, irritability, bruising or other skin changes

• toxins, environmental exposures, sick contacts, immunization status of close contacts (especially pertussis and influenza)

• history of trauma

• newborn screen results

Physical exam: The physical exam is subtle in young infants and neonates. Physical findings that merit specific attention in this age group include:

• fontanelle: bulging, flat, or sunken

• eyes: scleral icterus or subconjunctival hemorrhages; persistent downward gaze

• heart: murmur, gallop, symmetry of brachial and femoral pulses, four extremity blood pressures, capillary refill time

• lungs: accessory muscle use, stridor, wheeze, Kussmaul respiration

• abdomen: masses, organomegaly

• genitourinary: ambiguous genitalia

• skin: bruises, petechiae, vesicles, mottling, cyanosis, pallor

• neurological: tone, primitive reflexes

Diagnostic tests: In most cases, if there is not a clear history indicating an alternative diagnosis, the workup for an ill-appearing infant starts with a screen for sepsis and/or meningitis. Common tests to consider as indicated by history and/or physical exam findings include:

• blood and (catheterized) urine cultures

• cerebrospinal fluid (CSF) cell count and culture

• labs:

  • glucose, electrolytes, liver-function tests, complete blood count (CBC) with differential, ammonia, conjugated and unconjugated bilirubin, coagulation studies, urine and serum drug screens, inflammatory markers (C-reactive protein [CRP], erythrocyte sedimentation rate [ESR], procalcitonin), herpes simplex virus (HSV) polymerase chain reaction (PCR), venous or arterial blood gas

• EKG and/or echocardiogram

• imaging

  • chest radiograph

  • head CT

  • abdominal ultrasound

  • skeletal survey

  • electroencephalogram (EEG)

Fever in Young Infants

Fever is a common presenting symptom in infants younger than 2 months of age. Due to their immature immune systems, these infants are at high risk for serious bacterial illnesses (SBIs). Among febrile infants <60 days old, the prevalence of urinary tract infection (UTI) is >10%, bacteremia is <2%; and bacterial meningitis is <1%. Given the potentially catastrophic consequences of missed SBI in young infants, the standard of care is to rule out sepsis. Currently, the most common pathogens identified in febrile young infants with bacteremia are Escherichia coli and group B streptococcus (Streptococcus agalactiae).

Screening Criteria

For many decades, it was standard to perform full sepsis evaluations (including lumbar puncture) on all febrile infants <60 days of age, followed by hospitalization for parenteral antibiotics. However, in recent decades, research has identified criteria for infants at low risk for SBIs to reduce both unnecessary hospitalizations and antibiotic exposure. To date, there is no single universally accepted definition or set of screening criteria for “low risk.” Multiple data-driven guidelines have been published, and ED providers tend to practice according to the guideline of choice at their institution.

The three most common criteria for low risk originated from studies conducted in Boston, Philadelphia, and Rochester. Although each group defined “low risk” slightly differently, all three created algorithms that successfully predict which infants are unlikely to have bacterial meningitis.

In the last decade, many prediction rules for febrile young infants have evolved to include newer biomarkers that are more sensitive or more specific for SBI, mainly C-reactive protein and procalcitonin.

In 2016, Gomez et al. proposed a stepwise algorithm for determining risk among febrile young infants that was prospectively validated in 2185 febrile infants ≤90 days of age at 11 European pediatric EDs (4% had an invasive bacterial infection [IBI]). In the low-risk subgroup (991 infants), the prevalence of IBI was 0.7% and none of these infants had bacterial meningitis. The algorithm has a sensitivity of 92% and a negative predictive value of 99.3% for ruling out an IBI.

In 2019, Kuppermann et al. derived and prospectively validated a new clinical prediction rule to identify febrile infants younger than 60 days at low risk for SBIs using urinalysis, absolute neutrophil count (ANC), and procalcitonin levels at 26 US emergency departments. The prediction rule's sensitivity was 97.7%, specificity was 60.0% and negative predictive value was 99.6%. One infant with bacteremia and two infants with UTIs were misclassified and no infants with bacterial meningitis were missed. Once further validated, this rule can help reduce unnecessary lumbar punctures, antibiotic use, and hospitalizations even more.

In 2021, the American Academy of Pediatrics published clinical practice guidelines for the evaluation and management of well-appearing, full-term febrile infants 8 to 60 days of age. This guideline provides three age-based algorithms to help guide clinicians approach fever diagnostic evaluation and management for infants 8 to 21 days of age, 22 to 28 days of age, and 29 to 60 days of age.

Outcomes

In a 2010 review of 21 studies (8540 infants) published between 1985 and 2010, only 2 of 3984 infants who met low-risk criteria were diagnosed with bacterial meningitis. Both infants were younger than 29 days. No infant between 29 and 56 days of age who otherwise met low-risk criteria had bacterial meningitis. The results suggested that lumbar puncture (LP) may be safely excluded in infants between 29 and 56 days of age if they meet all other low-risk criteria.

Current literature suggests that the risk of meningitis in infants aged 22 to 28 days is lower than the risk in infants <22 days. Therefore, the 2021 AAP guidelines include an algorithm specifically for infants 22 to 28 days indicating that in some circumstances clinicians may elect to defer lumbar puncture.

Neonatal Herpes Simplex Virus (HSV)

Most neonates with HSV are born to mothers with asymptomatic genital herpes infection at delivery, and about one-third of neonates with HSV lack skin vesicles. As a result, practitioners should consider empiric HSV testing and treatment with acyclovir for any neonate who meets the following criteria:

• all infants <21 days old with fever or hypothermia

• any young infant with:

  • a mother with active primary HSV infection at delivery

  • skin vesicles on examination

  • seizure

  • CSF pleocytosis

  • increased liver enzymes

Treatment

For infants at high risk of serious bacterial infection (SBI), antimicrobial therapy is based on age and tailored to most common pathogens.

Pyloric Stenosis

Hypertrophic pyloric stenosis (HPS) refers to an idiopathic hypertrophy of the pylorus muscle that leads to obstruction of gastric outflow. The incidence of HPS is highest between 2 and 8 weeks of life, and is four times more common in male than female infants. Risk factors include postnatal macrolide exposure and family history of pyloric stenosis.

Clinical Presentation

• normal feeding in the first few weeks of life followed by development of worsening nonbilious emesis

• emesis gradually becomes forceful (often referred to as “projectile”) and can lead to dehydration

• soft, nondistended abdomen on physical exam (while classically described, you are rarely able to palpate an “olive” mass in mid-epigastrium)

• electrolyte imbalance (hypochloremia, hypokalemia, metabolic alkalosis)

Diagnosis

• ultrasound of the pylorus (increased diameter, thickness, and length)

Management

• nothing by mouth (NPO)

• rehydration with intravenous (IV) fluids

• surgical pyloromyotomy