NPS Exam :
Neonatal Pediatric Pathology Review

<BACK: Prepare for the Neonatal Pediatric Specialty Exam

One of the more challenging aspects of the neonatal pediatric specialty exam is the vast array of pathologies that the NPS test taker must be familiar with to be successful. While these pathologies and situations can be challenging, understanding a few basic generalities about the array of diseases found on the exam can be extremely helpful. Namely, recognizing that all pathologies and ailments can be categorized into two distinct areas – pulmonary problems and congenital defects or abnormalities.

While congenital defects among infants are far less common than are pulmonary issues during the first months after birth of a neonate, there are far more questions on the NPS exam addressing the congenital side of issues than there are pulmonary conditions. This focus makes it necessary for NPS exam candidates to gain a through understanding of nearly 15 congenital defects found among newborns.

Two Types of Neonatal Congenital Defects: Cardiac and Non-Cardiac related.

Cardiac Defects
When an infant is born with a cardiac defect, regardless of the kind of cardiac abnormality, the end result is improper directional blood flow. In normal conditions, within a few minutes after birth, the directional blood flow of the infant should change from directing blood through the mother’s placenta, to following the normal self-sustaining pathway of the infant’s own circulatory system. The conditions that cause these changes include a change in atmospheric pressure as the infant is suddenly exposed to normal atmospheric pressures, rather than the fluid-filled environment to which the fetus is accustomed. Additionally, the presence of oxygen in the atmosphere also encourages certain fetal blood passageways to close and redirect blood to the normal physiological pathways found in all mature human bodies.

However, sometimes these forces (atmospheric pressures and oxygen) fail to produce the desired anatomical closures and directional blood flow changes, resulting in failure of the infant to oxygenate tissues properly.

Generally speaking, whatever the abnormality, these kinds of directional blood flow concerns can the categorized into two types: Right-to-Left shunts and Left-to Right shunts. Each kind has its own set of clinical signs and physiologic challenges.

RIGHT-to-LEFT Shunting
In a normal neonate, blood is pumped from the right heart into the pulmonary system (the lungs) and then to the left heart for distribution to the systemic tissues of the body. However, in some neonatal congenital defects, blood bypasses the lungs and enters the left heart directly. The outcome is a severe lack of oxygenated blood in the systemic circulatory system and corresponding oxygen starvation of the tissues of the body. The reigning clinical characteristic that will be manifested by the neonate is central and peripheral cyanosis. This cyanotic condition will persist, regardless of changes in delivered FIO2 (fractional inspired oxygen percentage).

While neonatal pediatric specialists (respiratory therapist who have the special NPS designation), may not initially be aware of the congenital defect brewing inside, the condition becomes highly suspected when the infant fails to improve in color. Often, NPS therapists raise the delivered oxygen percentage only to discover it makes no difference in color of the newborn.

This response alone, the persistent cyanosis regardless of FIO2, is enough to suspect a congenital heart abnormality. Confirming examinations include chest radiography (X-rays) and other radiological and ultrasound procedures. Perhaps the best, most confirming exam is an echocardiogram. This ultrasound procedure offers a quick, affordable, non-invasive way to peer into the chest cavity to inspect the anatomical layout. With color-coded mapping, venous and arterial blood flow though the various chambers of the heart and corresponding vessels can be observed directly. Issues such as regurgitation, anatomical abnormalities, and misdirected blood flow can usually be spotted and diagnosed immediately.

The variety of diseases that include a RIGHT-to-LEFT shunt in neonates, and those that may be found on the neonatal pediatric specialty exam, include conditions such as atrial and ventricular septal defects, tetralogy of fallot.

LEFT-to-RIGHT Shunting
LEFT-to-RIGHT shunts present their own set of negative clinical circumstances but are often ultimately diagnosed in the same manner – echocardiography. However, in L-to-R shunts, the blood does not skip the lungs and, therefore, may be well oxygenated. Consequently, the presence of central cyanosis may not be as profound of a finding, compared to the R-to-L shunting cases.

In a L-to-R shunt, blood travels through the right heart normally and then is pumped into the pulmonary vascular bed. After receiving oxygen from the lungs, blood enters the left heart as part of normal circulatory function. However, it’s at this point that things go terribly wrong. Some congenital abnormalities consist of open pathways from the left heart directly back to the right heart, where the blood, once again, enters the lungs. The problems that stem from this circulatory pathway are largely two-fold: 1) Tissues of the body are deprived of adequate oxygenated blood and 2) the right heart begins to suffer from receiving blood volume from two sources – the normal blood through the vena cava and the extra blood from the left heart.

The general outcome related to L-to-R cardiac shunting in neonates is massive oxygen deprivation at the tissue level and right heart hypertension and failure.

There are a variety of conditions found in newborns that can cause L-to-R cardiac shunting but most involve septal defects between the ventricles of the heart. While a hole in the wall between atria or ventricles can cause either a R-to-L or a L-to-R shunting, the latter is more common among defects found the septal wall between the ventricles. Whether the blood shunts from the right to the left, or in the opposing direction, the blood’s movement between atria or ventricles is largely related to the strength of the contraction of the right vs. the left heart. In most cases, because the left heart is larger, and therefore stronger, the left ventricle overpowers the right ventricle and blood more naturally flows from L-to-R.

Transposition of the Great Vessels: A unique defect

One of the most consistently presented diseases on the neonatal pediatric specialist test (NPS exam) is that of Transposition of the Great Vessels. This very deadly congenital defect consists of an unexplainable anatomical change where the aorta and vent cava are switched. This causes the blood from the right heart to be pumped into a vessel that feeds directly back into the right heart, both drastically increasing pressure in the right heart and depriving the blood of oxygen. On the left side of the heart, blood is received from the pulmonary vascular bed into the left heart, only to be pumped right back into the pulmonary system. Essentially, transposition of the great vessels causes the formation of two independent loops of blood and two distinct problems: right heart failure and pulmonary hypertension.

The condition would almost always be deadly, were it not for the fact that most TGV conditions are also accompanied by a patent ductus arteriosis (PDA). This patent duct, a natural passageway that is supposed to close immediately on birth, allows some oxygenated blood to slip directly into the systemic vasculature, allowing for some tissue oxygenation, although still severely reduced and compromised.

The treatment, of course, is immediate surgery. But until the surgery can take place, the front-line defense is to keep the PDA from closing, as it naturally tries to do. Since the duct closes normally from its exposure to normal atmospheric oxygen when the infant is delivered, efforts are directed at decreasing the fraction of inspired oxygen (FIO2) to below the normal 21% that is found the natural atmosphere. Special devices are used to deliver oxygen percentages that approach 18% or further still, 16%.

Additionally, the PDA is encouraged to stay open by administering prostaglandins. If the chemical approach becomes ineffective, the duct may be opened or widened by a quick surgical procedure called the Rashkind Procedure. These strategies are employed until the more complex surgical correction of the problem may be planned and performed.

 

Pulmonary Pathologies found on the NPS exam

One of the most significant challenges on the Neonatal/Pediatric Specialty Exam (NPS exam) is the array of both pulmonary pathologies and congenital defects about which the would-be CRT or RRT NPS must demonstrate their knowledge. The author will focus on the pulmonary issues in this article. For more information on the array of congenital diseases, check out Neonatal Pediatric Specialty Exam Pathology Review: Congenital Pathologies.

Key NPS test Pulmonary Pathologies or Conditions:

Meconium Aspiration
Meconium is essentially fetal fecal matter. As the fetus develops in the mother’s womb, so does the intestinal tract of the fetus, along with it beginning stages of digestions. Consequently, fecal matter often develops in the bowels of the fetus prior to birth, but is retained until after birth, when the neonates experiences his or first bowel movement.

In some cases, however, this fecal matter is discharged by the infant in the amniotic sac prior to birth and begins to float around the amniotic fluid. While the infant does to respirate (breath) the amniotic fluid, the material, along with the fecal matter, does sometimes enter the fetal mouth. Upon birth, the fecal matter (meconium) can then sometimes be inadvertently inhaled by the neonate. When this happens, immediate action to clear the upper airway and lungs of the infant.

The early signs of the potential for meconium aspiration can be found first by visually assessing the amniotic fluid for the presence of meconium. This fecal material can often be visualized easily as small or large particulate matter in the fluid.

Perhaps more often than discovering the risk for meconium aspiration by evaluating the meconium, is the observed staining of the infant’s facial skin upon presentation. Meconium is often a dark green, tar like substance that, when it comes in contact with the skin, can stain the skin a light greenish-yellow. Health care team members to observe this perinatal sign are sure to take extra measure to clear the airway before the complete delivery of the infant. Delivering the infant, without regard to obvious meconium staining, can cause the infant in deeply aspirate the fecal matter upon the infant’s initial inspiration.

Once a meconium aspiration infant is born, diligent oral pharyngeal and bronchial hygiene is of paramount importance. During suction, because meconium can be thick and sticky, the endotracheal tube and/or suction catheters may become clogged. When this happens the preferred response on the neonatal pediatric specialty exam (NPS test) is to remove and discard clogged ET tubes or suction catheters. It is not prudent to attempt to clear these devices as time is of essence during meconium clearing attempts.

Premature birth seems to increase the incidence of meconium aspiration cases.

Bronchopulmonary Dysplasia
Also called Hyaline Membrane Disease, this condition usually results from long-term mechanical ventilation of the newborn. Most often, circumstances the lead to mechanical ventilation among BPD patients, include premature birth and infant respiratory distress syndrome.

The exact ideology is unknown but BPD often results in multiple system failure in the body. This is largely due to the negative impact of positive pressure on the hemodynamics of the patient as well as the implication of other osmotic changes that can occur when normal pressure gradients are disrupted.

Treatment usually includes a whole gamut of treatment, including diuretics, bronchodilators, corticosteroids, etc.

Other pulmonary conditions, common to the neonatal pediatric specialty exam, include pulmonary interstitial emphysema (PIE), pneumothracies, pneumonia, IRDS, to name a few.

Non-Cardiac Related Congenital Defects

Diaphragmatic Hernia
In rare cases, the diaphragm of a fetus fails to grow completely. Because the diaphragm serves as border between the chest and abdominal cavities, the incomplete development of the diaphragm allows abdominal contents to shift into the chest cavity, where bowels complete with the lungs for space.

The overall outcome of diaphragmatic hernia, and those issues observed on the neonatal pediatric specialty test, include:

• Consolidation in the low lung fields (from bowels in the chest cavity)
  
  
• Scaphoid abdomen (also called a sunken abdomen)
  
  
• Mediastinal shift
  
  
• More pronounced breath sounds on one side
  
  
• Diminished breath sounds overall

Resolution of diaphragmatic hernia requires surgical intervention, which should be schedule within a few days after its discovery. Until surgery can be performed, mitigating treatment includes use of lower ventilator pressure and constant evacuation of the stomach.

Esophageal Atresia
After birth, infants sometimes demonstrate an immediately complication during initial feeding attempts. The esophagus, which normally connects to the stomach, ends in a blind pouch just a few centimeters beyond the oral pharynx. Consequently, food, oral salivary secretions, and pulmonary secretions cannot be swallowed, as with normal infants.

The problem is most often discovered during initial feeding attempts, as bottle or breast feeding leads to immediate regurgitation and expectoration of the feeding material. A chest radiograph provides conclusive evidence and surgery is required to resolve the problem.

Prior to corrective surgery, the dead-end esophageal pouch must be kept clear of secretions and food material. To facilitate constant evacuation, a special device called a Replogle Tube is used. Inserted into the pouch, this device allows for the connection to suction, which keeps the pouch free of organic debris until corrective surgery can be performed.

Because the esophagus does not provide a pathway to the stomach, alternative routes of feeding must be used, such as enteral feeding, etc.

< Back: Prepare for the Neonatal Pediatric Specialty Exam