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<< The Nightmare Neonate: Life -Threatening Events In The First Month Of Life
Diagnostic Studies
During the initial ED stabilization and evaluation of any critically ill or comatose infant, many of the laboratory and radiological studies will be the same. Other, more individualized tests will depend on an evolving understanding of the patient’s history, physical examination, and response to resuscitative measures.
Bedside Tests
A bedside glucose should be obtained on all critically ill newborns. In one study, nearly 20% of children resuscitated for altered consciousness, status epilepticus, respiratory failure, cardiac failure, or cardiopulmonary arrest were hypoglycemic.65
A bedside hemoglobin test may aid in the rapid management of a patient with frank bleeding or pallor. A urine dipstick will detect the presence of ketones (which is associated with diabetic ketoacidosis and some inborn errors of metabolism) and leukocyte esterase and nitrites (associated with urinary tract infections). Specific gravity may not be as helpful in the neonatal period, as young infants are less able to concentrate their urine when dehydrated.
Obtain an ECG in newborns with extremes in heart rate, abnormal rhythms on the cardiac monitor, unexplained respiratory distress, shock, or heart murmurs. An upright T wave in V1 is normal until four days of life; beyond this period, consider underlying heart disorders and right ventricular hypertrophy.
In patients with suspected congenital heart disease, the hyperoxia test may assist in making the diagnosis. After obtaining a room air arterial blood gas or pulse oximeter reading, the cyanotic infant should be placed on 100% oxygen. If the oxygen saturation increases by more than 10% or the PO2 rises by more than 20%-30%, then the infant most likely has pulmonary pathology. If the oxygen saturation does not increase, then consider a congenital heart disorder.66 The hyperoxia test is not 100% sensitive or specific, as patients with large left-to-right shunts and hypoxia or mixing lesions with no pulmonary flow obstruction (such as total anomalous pulmonary venous return) may show large increases in oxygen saturations due to pulmonary arteriolar vasodilation.66
Laboratory Tests Sepsis Evaluation
Laboratory tests in febrile infants generally include a CBC, blood culture, urinalysis, and urine culture. A recent study of over 5000 infants evaluated for sepsis showed that the peripheral WBC count is unreliable and may be normal in the majority of infants with bacterial meningitis.67 A urinalysis should be obtained by catheterization or suprapubic aspiration (although this is being used less frequently), as bag urine is easily contaminated.68 If performing a sepsis work-up on an infant, perform a urine culture even if the urinalysis is completely normal. Some young children with a urinary tract infection have culture-proven infection despite lack of pyuria, nitrites, or a Gram’s stain demonstrating bacteria.69
The dictum to perform a lumbar puncture (LP) in all febrile children less than 28 days old has been called into question if the child is considered “low risk” by clinical and laboratory criteria.70 However, due to the higher propensity for meningitis, many authorities believe that an LP should be obtained in all of these patients. Due to the rapid clearance of recoverable organisms from the spinal fluid, an LP should be performed, if possible, prior to administration of antibiotics. However, if the patient is unstable or the LP is technically difficult to perform, then antibiotics should still be rapidly administered and the tap attempted later. Do not delay antibiotics in the ill-appearing child because you are unable to obtain spinal fluid.
Coagulation And Bleeding Studies
Several studies are useful in the case of the bleeding neonate. If the child is bleeding from the rectum and if ingested blood from a bleeding nipple is suspected, consider performing the Apt test, which differentiates maternal from fetal hemoglobin.71,72 This test is performed by adding one part of gastric contents or stool with five parts of water. After centrifuging, 0.1 mL of 0.2N sodium hydroxide is then added to the supernatant. A pink color is indicative of fetal hemoglobin, while a brown color suggests adult hemoglobin.
If a neonate presents with bruising or bleeding, order a CBC (including platelets), hepatic panel, prothrombin time, and partial thromboplastin time. Obtain a type and crossmatch in infants with significant bleeding
or hypotension.
Electrolytes
Electrolytes can be helpful in the management of patients with dehydration, shock, inborn errors of metabolism, congenital heart disease, and seizures. Farrar et al discovered that in infants less than 6 months old, prolonged seizures and temperatures lower than 36.5ºC were often associated with hyponatremia.73 Furthermore, hyponatremia was identified as the source of the seizure in 70% of infants younger than 6 months of age who lacked other causes.
Metabolic Studies
If congenital adrenal hyperplasia is suspected, draw a red top for 17-hydroxyprogesterone, dehydroepiandrosterone, androstenedione, and testosterone prior to administering hydrocortisone (or, if you can’t remember these tests in the heat of battle, draw and hold a red-top tube). If the child has signs of a hypermetabolic state, consider measurement of free T4 and thyroid-stimulating hormone levels.
Diagnostic evaluation for inborn errors of metabolism includes electrolytes, glucose, lactic acid, ammonia levels, and blood gas.74 Draw extra red- and green-top tubes of blood in case additional studies are ordered by the consultant. An anion gap of greater than 20 mmol/L is an important clue to an organic acidemia. Urinalysis may show spindle-shaped orotic acid crystals in urea cycle defects, and a urine pH of less than 5.5 suggests organic acidemia. Ask the lab to assess the urine for organic acids.
Tests For Jaundice
Well-appearing jaundiced neonates in the first few days of life require a fractionated bilirubin to determine the
need for admission. Ill-appearing neonates, those who develop jaundice more than a few days after birth, and those with high levels of total bilirubin also require a CBC for anemia, a peripheral blood smear for hemolysis, a reticulocyte count, and a Coomb’s test at the minimum. Many authorities would also recommend a sepsis work-up in this circumstance.
Additional Tests
A toxicology screen occasionally may be useful in the child with unexplained seizures.
Radiology Tests
A head CT or ultrasound should be obtained in newborns with seizures or change in mental status that is not obviously due to sepsis or metabolic causes. The results of these tests may be the first indication of child abuse, as infants often will not have any external evidence of trauma. An abdominal CT may also be indicated in newborns with unexplained vomiting. Solid organ injury may be associated with inflicted injuries.
A chest radiograph can identify cardiomegaly, pneumonia, pulmonary edema, rib fractures, and pneumothoraces. Posterior rib fractures are nearly pathognomonic for child abuse.75
Causes of cardiomegaly include congestive heart failure, myocarditis, over-hydration, pericardial effusion, and metabolic disturbances such as acidosis or hypoglycemia. The cyanotic infant with decreased vascular markings on the chest radiograph may have tetralogy of Fallot, pulmonary atresia, or tricuspid atresia; the cyanotic infant with increased markings may have transposition of the great arteries, total anomalous pulmonary venous return, or truncus arteriosus. The practitioner should suspect an endocardial cushion defect, ventricular septal defect, or patent ductus arteriosus in the acyanotic infant with increased pulmonary vascular markings.
The thymus may confound radiographic interpretation. This organ is large in neonates but is not typically seen after the age of 2 years.76 Radiographically, the enlarged thymus can obscure the right upper and middle lobes of the lung with a triangular, sail-shaped shadow projecting laterally from the anterior mediastinum. On a lateral radiograph, it occupies the anterior, superior mediastinal region. A film taken during inspiration can diminish its shadow and is useful when evaluating a possible infiltrate in this area. It is important to remember that the trachea is not displaced by a normal thymus.76
Abdominal films may yield signs of obstruction such as air fluid levels or paucity of gas throughout the intestines. Abdominal radiographs can also demonstrate the classic finding of tiny bubbles present in the gut wall (pneumatosis intestinalis) in necrotizing enterocolitis. In patients with Hirschsprung’s disease, abdominal radiographs may reveal signs of obstruction, and a barium enema will show a cone-shaped transition zone with a dilated segment of proximal colon.
Children with malrotation and midgut volvulus will often demonstrate a “double-bubble sign,” with an overall paucity of gas with two air bubbles, one in the duodenum and one in the stomach (also seen with gastric atresia). (See Figure 2.) The upper gastrointestinal series, which is currently the gold standard for diagnosis, shows right-sided small intestinal rotation with narrowing of the contrast at the site of obstruction. “Cork-screwing” is the spiraling of the small intestine around the superior mesenteric artery. An ultrasound may confirm a distended, fluid-filled duodenum and dilated loops of small bowel to the right of the spinal column.
An abdominal ultrasound can also assist with the diagnosis of pyloric stenosis by demonstrating a pyloric wall greater than 4 mm and a canal length of greater than 14 mm. An upper gastrointestinal series reveals the “string sign,” which consists of contrast going through the stenotic and elongated channel.
A complete skeletal survey should be performed in patients suspected of being abused.28
“It didn’t take elaborate experiments to deduce that an infant would die from want of food. But it took centuries to figure out that infants can and do perish from want of love.” —Louise J. Kaplan, in “No Voice Is Ever Wholly Lost,” 1995
Bedside Tests
A bedside glucose should be obtained on all critically ill newborns. In one study, nearly 20% of children resuscitated for altered consciousness, status epilepticus, respiratory failure, cardiac failure, or cardiopulmonary arrest were hypoglycemic.65
A bedside hemoglobin test may aid in the rapid management of a patient with frank bleeding or pallor. A urine dipstick will detect the presence of ketones (which is associated with diabetic ketoacidosis and some inborn errors of metabolism) and leukocyte esterase and nitrites (associated with urinary tract infections). Specific gravity may not be as helpful in the neonatal period, as young infants are less able to concentrate their urine when dehydrated.
Obtain an ECG in newborns with extremes in heart rate, abnormal rhythms on the cardiac monitor, unexplained respiratory distress, shock, or heart murmurs. An upright T wave in V1 is normal until four days of life; beyond this period, consider underlying heart disorders and right ventricular hypertrophy.
In patients with suspected congenital heart disease, the hyperoxia test may assist in making the diagnosis. After obtaining a room air arterial blood gas or pulse oximeter reading, the cyanotic infant should be placed on 100% oxygen. If the oxygen saturation increases by more than 10% or the PO2 rises by more than 20%-30%, then the infant most likely has pulmonary pathology. If the oxygen saturation does not increase, then consider a congenital heart disorder.66 The hyperoxia test is not 100% sensitive or specific, as patients with large left-to-right shunts and hypoxia or mixing lesions with no pulmonary flow obstruction (such as total anomalous pulmonary venous return) may show large increases in oxygen saturations due to pulmonary arteriolar vasodilation.66
Laboratory Tests Sepsis Evaluation
Laboratory tests in febrile infants generally include a CBC, blood culture, urinalysis, and urine culture. A recent study of over 5000 infants evaluated for sepsis showed that the peripheral WBC count is unreliable and may be normal in the majority of infants with bacterial meningitis.67 A urinalysis should be obtained by catheterization or suprapubic aspiration (although this is being used less frequently), as bag urine is easily contaminated.68 If performing a sepsis work-up on an infant, perform a urine culture even if the urinalysis is completely normal. Some young children with a urinary tract infection have culture-proven infection despite lack of pyuria, nitrites, or a Gram’s stain demonstrating bacteria.69
The dictum to perform a lumbar puncture (LP) in all febrile children less than 28 days old has been called into question if the child is considered “low risk” by clinical and laboratory criteria.70 However, due to the higher propensity for meningitis, many authorities believe that an LP should be obtained in all of these patients. Due to the rapid clearance of recoverable organisms from the spinal fluid, an LP should be performed, if possible, prior to administration of antibiotics. However, if the patient is unstable or the LP is technically difficult to perform, then antibiotics should still be rapidly administered and the tap attempted later. Do not delay antibiotics in the ill-appearing child because you are unable to obtain spinal fluid.
Coagulation And Bleeding Studies
Several studies are useful in the case of the bleeding neonate. If the child is bleeding from the rectum and if ingested blood from a bleeding nipple is suspected, consider performing the Apt test, which differentiates maternal from fetal hemoglobin.71,72 This test is performed by adding one part of gastric contents or stool with five parts of water. After centrifuging, 0.1 mL of 0.2N sodium hydroxide is then added to the supernatant. A pink color is indicative of fetal hemoglobin, while a brown color suggests adult hemoglobin.
If a neonate presents with bruising or bleeding, order a CBC (including platelets), hepatic panel, prothrombin time, and partial thromboplastin time. Obtain a type and crossmatch in infants with significant bleeding
or hypotension.
Electrolytes
Electrolytes can be helpful in the management of patients with dehydration, shock, inborn errors of metabolism, congenital heart disease, and seizures. Farrar et al discovered that in infants less than 6 months old, prolonged seizures and temperatures lower than 36.5ºC were often associated with hyponatremia.73 Furthermore, hyponatremia was identified as the source of the seizure in 70% of infants younger than 6 months of age who lacked other causes.
Metabolic Studies
If congenital adrenal hyperplasia is suspected, draw a red top for 17-hydroxyprogesterone, dehydroepiandrosterone, androstenedione, and testosterone prior to administering hydrocortisone (or, if you can’t remember these tests in the heat of battle, draw and hold a red-top tube). If the child has signs of a hypermetabolic state, consider measurement of free T4 and thyroid-stimulating hormone levels.
Diagnostic evaluation for inborn errors of metabolism includes electrolytes, glucose, lactic acid, ammonia levels, and blood gas.74 Draw extra red- and green-top tubes of blood in case additional studies are ordered by the consultant. An anion gap of greater than 20 mmol/L is an important clue to an organic acidemia. Urinalysis may show spindle-shaped orotic acid crystals in urea cycle defects, and a urine pH of less than 5.5 suggests organic acidemia. Ask the lab to assess the urine for organic acids.
Tests For Jaundice
Well-appearing jaundiced neonates in the first few days of life require a fractionated bilirubin to determine the
need for admission. Ill-appearing neonates, those who develop jaundice more than a few days after birth, and those with high levels of total bilirubin also require a CBC for anemia, a peripheral blood smear for hemolysis, a reticulocyte count, and a Coomb’s test at the minimum. Many authorities would also recommend a sepsis work-up in this circumstance.
Additional Tests
A toxicology screen occasionally may be useful in the child with unexplained seizures.
Radiology Tests
A head CT or ultrasound should be obtained in newborns with seizures or change in mental status that is not obviously due to sepsis or metabolic causes. The results of these tests may be the first indication of child abuse, as infants often will not have any external evidence of trauma. An abdominal CT may also be indicated in newborns with unexplained vomiting. Solid organ injury may be associated with inflicted injuries.
A chest radiograph can identify cardiomegaly, pneumonia, pulmonary edema, rib fractures, and pneumothoraces. Posterior rib fractures are nearly pathognomonic for child abuse.75
Causes of cardiomegaly include congestive heart failure, myocarditis, over-hydration, pericardial effusion, and metabolic disturbances such as acidosis or hypoglycemia. The cyanotic infant with decreased vascular markings on the chest radiograph may have tetralogy of Fallot, pulmonary atresia, or tricuspid atresia; the cyanotic infant with increased markings may have transposition of the great arteries, total anomalous pulmonary venous return, or truncus arteriosus. The practitioner should suspect an endocardial cushion defect, ventricular septal defect, or patent ductus arteriosus in the acyanotic infant with increased pulmonary vascular markings.
The thymus may confound radiographic interpretation. This organ is large in neonates but is not typically seen after the age of 2 years.76 Radiographically, the enlarged thymus can obscure the right upper and middle lobes of the lung with a triangular, sail-shaped shadow projecting laterally from the anterior mediastinum. On a lateral radiograph, it occupies the anterior, superior mediastinal region. A film taken during inspiration can diminish its shadow and is useful when evaluating a possible infiltrate in this area. It is important to remember that the trachea is not displaced by a normal thymus.76
Abdominal films may yield signs of obstruction such as air fluid levels or paucity of gas throughout the intestines. Abdominal radiographs can also demonstrate the classic finding of tiny bubbles present in the gut wall (pneumatosis intestinalis) in necrotizing enterocolitis. In patients with Hirschsprung’s disease, abdominal radiographs may reveal signs of obstruction, and a barium enema will show a cone-shaped transition zone with a dilated segment of proximal colon.
Children with malrotation and midgut volvulus will often demonstrate a “double-bubble sign,” with an overall paucity of gas with two air bubbles, one in the duodenum and one in the stomach (also seen with gastric atresia). (See Figure 2.) The upper gastrointestinal series, which is currently the gold standard for diagnosis, shows right-sided small intestinal rotation with narrowing of the contrast at the site of obstruction. “Cork-screwing” is the spiraling of the small intestine around the superior mesenteric artery. An ultrasound may confirm a distended, fluid-filled duodenum and dilated loops of small bowel to the right of the spinal column.
An abdominal ultrasound can also assist with the diagnosis of pyloric stenosis by demonstrating a pyloric wall greater than 4 mm and a canal length of greater than 14 mm. An upper gastrointestinal series reveals the “string sign,” which consists of contrast going through the stenotic and elongated channel.
A complete skeletal survey should be performed in patients suspected of being abused.28
“It didn’t take elaborate experiments to deduce that an infant would die from want of food. But it took centuries to figure out that infants can and do perish from want of love.” —Louise J. Kaplan, in “No Voice Is Ever Wholly Lost,” 1995
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