LECTURE FIVE
RESPIRATORY TRACT DISORDERSRespiratory disorders are the most frequent cause of admission for neonatal intensive care in both term and preterm infants . signs and symptoms of respiratory distress include cyanosis , grunting , nasal flaring retraction, tachypnea , decreased breath sounds with or without rales and pallor .
The first breath :
Initiation of the first breath is caused by a decline in Pao2 and PH and a rise in Paco2 as a result of interruption of the placental circulation , a redistribution of cardiac output , a decrease in body temperature and various tactile and sensory inputs .Hyaline membrane disease (respiratory distress syndrome of newborn )
Is a respiratory disorder that primarily affects preterm infants who are born before the biochemical maturation of their lungs .Biochemical development : the most important prenatal event is the production of surfactant by type II alveolar cells .
The major function of surfactant is to decrease alveolar surface tension and increasing lung compliance . surfactant prevent alveolar collapse at the end of expiration and allows for opening of the alveoli at a low intra-thoracic pressure . the ratio of lecithin to sphingomyelin in the aminiotic fluid is areflection of the amount of intrapulmonary surfactant and lung maturity .an L/S ratio of 2:1 or greater usually indicates biochemical lung maturity .
Surfactant increase by ( steroid administration , prolonged membrane rupture ,preeclampsia , placental insufficiency , thyroide hormone , theophyline ).
Surfactant decreased by ( maternal diabetes , acute asphyxia ) .
Pathophysiology . the lungs are poorly compliant owing to deficiency of surfactant resulting in classic complex of progressive atelectasis , intrapulmonary shunting , hypoxemia ,and cyanosis .the hyaline membrane that forms and lines the alevioli is composed of protein and sloughed epithelium – the result of oxygen exposure , alveolar capillary leakage and the forces generated by the mechanical ventilation of these infants .
Clinical features: affected infants characteristically present with tachypnea , grunting , nasal flaring , chest retraction ,and cyanosis , in first three hours of life . there is decrease air entry on auscultation .apnea and irregular respiration are ominous sign requiring immediate action .respiratory failure may occur in severe course
Clinical course : the natural course is a progressive worsening over the first 48- 72 hrs of life .
After the initial insult to the airway lining , the epithelium is repopulated with type II alveolar cells .
Subsequently , there is increase production and release of surfactant , so that there are sufficient quantities in the air spaces by 72 hrs of life .this result in improvement in lung compliance and resolution of the respiratory distress .
Diagnosis :is confirmed by a chest radiograph that reveals a uniform ground-glass pattern and an air bronchogram that is consistent with a defuse atelectasis , clinical manifestation and gas analysis .
RDS should be differentiated from ( early onset sepsis , pneumonia , cyanotic heart diseases , aspiration syndromes , spontaneous pneumothorax , transient tachypenia of newborn .) .
Therapy and prognosis :
Conventional therapy for the affected premature infant include supportive care as well as the administration of oxygen . it also necessary to increase the main airway pressure by use of continuous positive airway pressure , intermittent assisted ventilation , or a high frequency oscillation . outcome with conventional therapy is good .
Exogenous surfactant replacement therapy with artificial or bovine surfactant has become an important intervention for those infants with severe surfactant deficiency . alveolar opening and improvement in oxygenation and ventilation occur almost immediately .
Prevention . when amniotic fluid assessment reveals fetal lung immaturity and preterm delivery can not be prevented , administration of corticosteroid to the mother 48 hrs before delivery can induce or accelerate the production of fetal lung surfactant .
Complications :common complications and associated findings include pneumothorax , patent ductus arteriosus , intraventricular hemorrhage , necrotizing enterocolitis , bronchopulmonary dysplasia and retinopathy of prematurity .
Transient tachypnea of newborn :
Is thought to result from decreased lymphatic absorption of fetal lung fluid It most commonly occurs in the infant born near term by cesarean section ,without preceding labor ( the catecholamine surge associated with labor and delivery which is thought to enhance pulmonary lymphatic drainage does not occur in this setting )
(1)- clinical features . the tachypnea is quiet or mild and usually not associated
with retraction . the infant appears comfortable and rarely cyanotic .
(2)- diagnosis : is based on the delivery and chest radiograph ,which
characterized by fluid in the major fissure , prominent vascular marking ,
increased interstitial markings and hyperinflation . auscultation may
reveal rales .
(3)- therapy is supportive . the tachypnea resolves in a few days .low doses of
supplemental oxygen may be required .
persistent of the fetal circulation( persistent pulmonary hypertension ).
Usually a disease of term infants who are experience acute or chronic in utero hypoxia .it is seen frequently in infant with meconium aspiration syndrome .Pathophysiology . the primary abnormality is a failure of the pulmonary vascular resistance to fall with postnatal lung expansion and oxygenation .
Normally at birth the systemic vascular resistance rises as a result of cessation of blood flow through the placenta , and pulmonary vascular resistance falls with the first breath .
With persistence of the fetal circulation , the pulmonary vascular resistant continues to be high and may in fact be higher than the systemic resistance .this result in shunting of the deoxygenated blood which is returning to the right side of the heart away from the lungs. The right to left shunt can occur at both the atrial level(foramen of ovale ) and through the ductus arteriosus .because the lung are bypassed the blood is not oxygenated and hypoxemia ensues.
Clinical features . these infants have rapidly progressive cyanosis associated with mild to severe respiratory distress . there is a varied response to oxygen administration depending on the size of the shunt .
Diagnosis :
The diagnosis is suggested by a history of perinatal asphyxia and clinical cyanosis at birth combined with a negative cardiovascular examination and negative chest radiograph , although parenchymal disease may coexist ( MAS,RDS ) .
Echocardiography should be used to establish the diagnosis and should demonstrate :
(!) the absence of cyanotic heart disease .
(!!) an increased pulmonary vascular resistance .
(!!!) the presence of right to left shunt at the foramen of ovale ductus
arteriosus , or both .
Therapy : include supplemental oxygen , mechanical ventilation , hyperventilation ,support of systemic blood pressure and administration of sodium bicarbonate and pulmonary vasodilators .
Prognosis : the overall mortality rate associated with this disease is high .extra-corporeal membrane oxygenation may improve the outcome .
Apnea
Apnea is cessation of breathing for longer than 20 seconds . apnea often occurs in preterm infants ( apnea of prematurity ) and reflect immaturity of the respiratory control mechanism in the brain stem .
(1)- clinical features ,bradycardia ( HR less than 80beats/min ) often associated with apnea .apnea of prematurity is characterized by periodic breathing and intermittent hypoxia , which further diminish respiratory derive .
(2)- diagnosis . of apnea of prematurity is made after excluding other reason for the apnea like :
Respiratory ( pneumonia , airway obstruction, hypoxia , pneumothorax ).
CNS ( intracranial hemorrhage , seizure , drugs ,hypoxic injury ).
Infections ( sepsis , meningitis ).
Metabolic ( hypoglycemia , hypocalcemia , decrease or increase sodium , hypothermia ).
Cardiovascular ( heart failure , hypotension , ).
Gasrtointestinal ( necrotizing enterocolitis , ).
(3)- therapy : therapy of apnea of prematurity include one of the following :
a- tactile stimulation
b--maintain body temperature .
supplemental oxygen .
administration of respiratory stimulant ( theophyline , caffeine )
use continuous positive air way or intermittent assisted ventilation ) .
treatment of underling cause .
prognosis : apnea of prematurity does not alter prognosis unless it severe , recurrent and refractory to therapy ).
Choanal atresia : is a unilateral or bilateral obstruction of the posterior nasal airway by a membrane or bony septum .this life threatening anomaly result from failure of the bucconasal mucosa to rupture .
Clinical features : because most newborn are obligate nose breathers , bilateral atresia usually presents in the delivery room as airway obstruction , apnea and cyanosis .distressed neonate then cry which relieve the cyanosis . unilateral obstruction may be asymptomatic .
Diagnosis : is confirmed either by inability to pass a suction catheter through the nostril into the oropharynx or by radiography using radioopaque dye to show the area of nasal obstruction .
Therapy : emergency management consists of establishing an airway either with an oral airway or by endotracheal intubation . definitive therapy is surgical reconstruction performing in neonatal period .
Diaphragmatic hernia :
Diaphragmatic hernia is a displacement of the abdominal content into the thoracic cavity through a defect in the diaphragm .Types :
hernias through the foramen of bochdalek are by far the most commonly seen diaphragmatic hernia . the defect , which almost always is on the left occurs in the posteriolateral portion of the diaphragm . it results from failure of the pleuroperitoneal canal to close , which normally occurs between 6-8 wks gestation.
Herians through the foramen of morgagni are somewhat rare , the hernia usually on the right .frequently the hernia contain only omentum and the affected newborn is asymptomatic .
Pathophysiology : ipsilateral pulmonary hypoplasia results from compression of the affected lung by the displaced gastrointestinal organs a shift of the mediastinal structures resulting in compression of the contralateral lung may cause hypoplasia of the lung to a lesser degree .
Diagnosis : is confirmed by a chest radiograph demonstrating air-filled bowel in the hemithorax .
Therapy : includes intubation , vigorous oxygenation and mechanical ventilation , decompression of the intestinal tract with a nasogastric tube , correction of metabolic acidosis , and surgical removal of the abdominal contents from the thorax with repair of the hernia .
Mask and bag ventilation should be avoided or minimized because it results in distension of the bowel and further compromises the pulmonary function of the affected newborn .
Pulmonary hypertension frequently complicates the preoperative and postoperative course .
Extracorporeal membrane oxygenation may be helpful in selected infants .
Prognosis : survival rates depend on the degree of the lung hypoplasia and the presence of other anomalies ,symptoms before 24 hrs of age , herniation to the contralateral lung and need for ECMO . with conventional therapy , survival rates are approximately 67% , however the use of extracorporeal membrane oxygenation may improve survival .
Meconium aspiration syndrome (MAS)
MAS is a multiorgan disorder with perinatal asphyxia as the underlying cause . it is most commonly occurs in post term infants and in infants who are small for gestational age due to intrauterine growth retardation . both have placental insufficiency as a common for fetal hypoxia .
Pathophysiology . the fetal hypoxia triggers via a vagal reflex , the passage of thick meconium into the amniotic fluid .the contaminated amniotic fluid is swallowed into the oropharynx and aspirated at birth with the initiation of breathing . with severe fetal asphyxia and acidosis , the meconium may be aspirated prenatally because of fetal gasping .other organ affected by the perinatal hypoxia include the brain ,heart gastrointestinal tract and kidneys .
Diagnosis : is established by the presence of mecomium in the tracheal or amniotic fluid combined with symptoms of respiratory distress and a chest radiograph that reveals a pattern of diffuse infiltrate with hyperinflation .
Therapy : because most episodes of aspiration occur with the initiation of respiration , the most effective therapy is prevention . this consist of removal of the meconium before the initiation of ventilation . the meconium is removed from the infant airway as follows:
The oropharynx is suctioned before both delivery of the thorax and initiation of breathing ,and again when the infant is on the warmer bed .
The vocal cords are visualized using a laryngoscope , and a large endotracheal tube or DeLee catheter is inserted .
Direct wall-unit suction is applied to the tube or catheter as it is removed . this procedure is repeated if significant meconium is removed . only after the trachea is cleared of any meconium should spontaneous or artificial ventilation be initiated .
If aspiration has occurred and the infant is in distress , therapy consists of administration of oxygen and mechanical ventilation .
Persistent pulmonary hypertension also may coexist and should be vigorously treated .
Pneumothorax :
Pneumothorax is presence of free air in the pleural space . the air often is under pressure and in this setting is referred to as tension pneumothorax .Incidence and etiology . asymptomatic , spontaneous pneumothorax occurs in 1-2% of otherwise healthy newborn at birth . symptomatic pneumothorax more commonly occurs in the infant who is receiving mechanical ventilation or who has underling lung disease ( RDS, MAS) .
Clinical manifestations . symptoms and signs include cyanosis , tachypnea ,and elevation of the affected hemithorax . auscultation reveals diminished breath sounds on the affected side .
Diagnosis :
The diagnosis made by a chest radiograph that demonstrate a dense partially collapsed lung surrounded by a large area of radiolucent air within the hemithotax . depending on the degree of tension and lung compliance , the mediastinal structures are shifted toward the opposite side of the chest .
Transillumination of the thorax may aid in the diagnosis of the pneumothrax in the emergencies , positive evidence is the transmission of light through the affected side .
Therapy :varies with the severity of the symptoms .
If no other lung disease exists and there is minimal respiratory distress , supplemental 100% oxygen ( nitrogen wash out technique ) for several hours usually is sufficient .
If a significant degree of tension , respiratory distress ,or some other lung disease exist the air should be evacuated by aspiration with a syringe and needle or by a chest tube if a continuous air leak exists .