Полезные материалы за все 6 курсов / Учебники, методички, pdf / Kaplan Pediatrics USMLE 2CK 2021

Chapter 1 λ The Newborn

Hearing Loss

Pediatric hearing loss is more prevalent than diabetes mellitus and all childhood cancers. A ­universal newborn hearing screening is recommended prior to newborn discharge, with the goal of evaluating all hearing loss by age 3 months. Usually the otoacoustic emissions test (OAE) is used, where a small earphone/microphone is placed in the ear and sounds are played.

•If hearing is normal, an echo is reflected back into the ear canal and is measured by the microphone.

•If hearing is not normal (patient does not pass), newborns are given the auditory brainstem response test (ABR) (most accurate hearing measure through age 6 months). Sounds are presented through a small earphone, measured with head electrodes, and analyzed by a computer.

•Normal OAE: intact hearing through the cochlea

•Normal ABR: also establishes the integrity of the auditory nerve

As for the causes of hearing loss, up to 60% prelingual is genetic (>60 gene loci, >500 syndromes with hearing loss); 70-80% is autosomal recessive, with 50% having a defect in connexin 26 (a gap junction protein). Examples include Waardenburg syndrome (most common autosomal dominant condition with hearing loss), neurofibromatosis-2 (AD), Alport syndrome (AR).

Up to 25% are nongenetic and up to 25% are idiopathic. Examples include CMV (most common congenital cause; then other congenital infections); otitis media with effusion (OME) (most common childhood cause); bacterial meningitis, especially pneumococcus (occurs early and in >30%); trauma, especially to temporal bone; medication (aminoglycosides, loop diuretics, cisplatin); acoustic (loud music, especially with earbuds/phones; audiograms show high-frequency loss at 4,000 Hz).

FETAL GROWTH AND MATURITY

Table 1-5. Intrauterine Growth Restriction (IUGR)

Chapter 1 λ The Newborn

–Renal vein thrombosis (flank mass, hematuria, thrombocytopenia) from polycythemia

–Increased incidence of congenital anomalies

°Cardiac—especially VSD, ASD, transposition

°Small left colon syndrome (transient delay in development of left side of colon; presents with abdominal distention)

°Caudal regression syndrome: spectrum of structural neurologic defects of the caudal region of spinal cord which may result in neurologic impairment (hypo, aplasia of pelvis & LE)

•Prognosis—Infants of diabetic mothers are more predisposed to diabetes and LGA infants are at increased risk of childhood obesity.

•Treatment—careful monitoring and glucose control during pregnancy + close monitoring of infant after delivery; early frequent feeds (oral, NG if hypoglycemia continues) followed by IV dextrose if euglycemia has not resulted

Clinical Recall

Which of the following is commonly seen in infants of diabetic mothers?

A.Microsomia

B.Small heart size

C.Polycythemia

D.Renal artery thrombosis

E.Slow respiratory rate

Answer: C

RESPIRATORY DISORDERS

Respiratory Distress

Pneumonia

Diaphragmatic hernia

Choanal atresia

Figure 1-1. Respiratory Distress

Chapter 1 λ The Newborn

•Prevention—endotracheal intubation and airway suction of depressed infants with thick meconium

•Treatment—positive pressure ventilation and other complex NICU therapies

Diaphragmatic Hernia

•Failure of the diaphragm to close → abdominal contents enter into chest, causing pulmonary hypoplasia.

•Born with respiratory distress and scaphoid abdomen

•Bowel sounds may be heard in chest

•Diagnosis—prenatal ultrasound; postnatal x-ray (best test) reveals bowel in chest

•Best initial treatment—immediate intubation in delivery room for known or suspected CDH, followed by surgical correction when stable (usually days)

GASTROINTESTINAL AND HEPATOBILIARY DISORDERS

See also GI chapter on this topic.

Umbilical Hernia

•Failure of the umbilical ring closure, weakness of abdominal muscles

•Most are small and resolve in 1-2 years without any treatment

•Surgery if getting larger after 1-2 years, symptoms (strangulation, incarceration), and/or persistent after age 4

Omphalocele

•Failure of intestines to return to abdominal cavity with gut through umbilicus at 11 weeks’ gestation

•Covered in a sac (protection)

•Associated with other major malformations and possible genetic disorders (trisomy)

•Large defects need a staged reduction (use of a surgical Silo), otherwise respiratory failure and ischemia

Gastroschisis

•Defect in abdominal wall lateral to umbilicus (vascular accident; typically not associated with other malformations)

•Any part of the GI tract may protrude

•Not covered by a sac

•Major problem with the intestines: atresia, stenosis, ischemia, short gut

•Surgery based on condition of gut; if no ischemia, large lesions need a staged reduction as with omphalocele

USMLE Step 2 CK λ Pediatrics

10

Chapter 1 λ The Newborn

The causes of hyperbilirubinemia with respect to bilirubin metabolism are as follows:

•RBC metabolism

––Increased RBCs

°° Physiologic jaundice (healthy newborn [normal Hct 42−65]) °° Polycythemia (Hct >65)

i.Increased RBC production: Chronic hypoxia, IUGR, post-mature; IODM, Beckwith-Wiedemann syndrome (insulin effect); trisomies (unknown mechanism)

ii.Extra RBCs entering the circulation: delayed cord clamping, twin-twin transfusion

iii.Treatment: partial exchange transfusion with normal saline (dilutional)

––Increased hemolysis

°° Immune-mediated (labs: high unconjugated bilirubin, may be anemia, increased reticulocyte count, positive direct Coombs test)

i.Rh negative mother/Rh positive baby: classic hemolytic disease of the newborn (erythroblastosis fetalis)

ii.ABO incompatibility (almost all are type O mother and either type A or B baby): most common reason for hemolysis in the newborn

iii.Minor blood group incompatibility (Kell is very antigenic; Kell negative mother), uncommon

°° Non-immune mediated: same as above but Coombs is negative; need to see blood smear

i.Smear shows characteristic-looking RBCs: membrane defect (most are either spherocytosis or elliptocytosis)

ii.Smear shows normal-looking RBCs: enzyme defect (most are G6PD deficiency then pyruvate kinase deficiency)

iii.Extravascular: excessive bruising, cephalohematoma

•Bilirubin is then bound to albumin and carried in the blood; bilirubin may be uncoupled­ from albumin in the bloodstream to yield free bilirubin, e.g. neonatal sepsis, certain drugs (ceftriaxone), hypoxia, acidosis.

•Bilirubin is transported to the hepatocytes: within the hepatocytes is the conversion of unconjugated (laboratory indirect-acting) fat-soluble bilirubin to conjugated (glucuronide) water-soluble bilirubin (laboratory direct-acting) by the action of hepatic glucuronyl transferase (GT).

––Decreased enzymatic activity of GT

°° Normal newborn first week of life

°° Primary liver disease of systemic disease affecting the liver (sepsis, TORCH, metabolic diseases)

°° No GT activity: Crigler-Najjar syndrome (type I)

USMLE Step 2 CK λ Pediatrics

•Transport through the intrahepatic biliary system to the porta hepatis for excretion into the duodenum; abnormalities of transport and excretion cause a conjugated (direct) hyperbilirubinemia (>2 mg/dL direct-acting bilirubin in the blood in the newborn).

–– Biliary atresia (progressive obliterative cholangiopathy): obstruction at birth due to fibrosis and atresia of the extrahepatic ducts (and so no gall bladder); then variable severity and speed of inflammation and fibrosis of the intrahepatic system which ultimately leads to cirrhosis

°° Most accurate test (next step): percutaneous liver biopsy (is pathognomonic for this process)

°° Best initial treatment (palliative): hepatic portojejunostomy (Kasai procedure)

°° Best long-term management: liver transplant

––Liver disease (primary or secondary to systemic disease): cholestasis (sepsis, perinatal infections, metabolic disease, neonatal hepatitis, severe hypothyroidism and others)

•Intestinal transport and excretion: most bilirubin is eliminated in the stool with final products synthesized with help of colonic bacteria; some bilirubin is eliminated in the urine, some is reprocessed in the liver due to enterohepatic circulation (along with bile acids); intestinal beta-glucuronidase hydrolyzes glucuronide-bilirubin bonds to yield some unconjugated bilirubin, which is absorbed into the portal circulation and transported back to the liver to be acted upon by hepatic glucuronyl transferase

––Increased enterohepatic circulation

°° Intestinal obstruction

°° Decreased colonic bacteria (first week of life, prolonged antibiotics, severe diarrhea)

°° Breastfeeding jaundice (due to decreased intestinal peristalsis)

°° Breast-milk jaundice (due to excessive concentration of glucuronidase in breast milk)

Clinical Recall

Which of the following is not a cause of hyperbilirubinemia?

A.Increased red blood cell production

B.ABO incompatibility

C.Biliary atresia

D.Increased activity of hepatic glucuronyl transferase

E.Decreased enterohepatic circulation

Answer: D

12

Chapter 1 λ The Newborn

Breastfeeding Jaundice Versus Breast-Milk Jaundice

Breastfeeding jaundice means a baby is not getting enough calories through nursing. It occurs in the first few days of life and is common in first-time breastfeeding mothers. While the infant may become dehydrated, lack of calories is what causes the jaundice. In the absence of food in the

intestines, peristalsis decreases significantly, allowing much more time for intestinal beta-glucuronidase to hydrolyze the glucuronide bonds and produce more unconjugated (indirect-acting) bilirubin. This enters the portal circulation and is transported back to the liver for further action by hepatic glucuronyl transferase. The result is increased unconjugated bilirubin and increased enterohepatic circulation. Treatment is to obtain a lactation consultation and rehydrate the baby.

Breast-milk jaundice (week 2 of life) is caused by increased glucuronidase in breast milk. More glucuronides are hydrolyzed in the intestine, producing more indirect bilirubin and again increasing enterohepatic circulation. The problem is temporary, because the activity of this enzyme decreases steadily over the first 2–3 months of life and then ceases. Treatment is phototherapy if needed. Bilirubin may rise again, but not to the previous level. The baby may then be safely breastfed.