Presentation on theme: "Objectives : Definition of MAS Background Epidemiology Pathophysiology How MAS induce hypoxia ? Remember Physical examination. Air leak syndromes - pulmonary."— Presentation transcript:
Defintion : mixture of meconium and amniotic fluid Meconium aspiration syndrome is a serious condition in which a newborn breathes a mixture of meconium and amniotic fluid into the lungs around the time of delivery.
Background The first intestinal discharge from newborns is meconium. Meconium is a viscous, dark-green substance composed of intestinal epithelial cells, lanugo, mucus, and intestinal secretions (eg, bile). the 3 major solid constituents of meconium : - Intestinal secretions. - mucosal cells. - and solid elements of swallowed amniotic fluid.
Conti.. Water is the major liquid constituent, comprising 85- 95% of meconium. Meconium is sterile and does not contain bacteria, the primary factor that differentiates it from stool. Intrauterine distress can cause passage into the amniotic fluid.
Conti.. Factors that promote the passage in utero include : 1- placental insufficiency 2- maternal hypertension 3- preeclampsia 4- oligohydramnios, and 5-maternal drug abuse, especially of tobacco and cocaine 6-Maternal infection/chorioamnionitischorioamnionitis 7-Fetal hypoxia
Conti.. Meconium-stained amniotic fluid may be aspirated before or during labor and delivery. Because meconium is rarely found in the amniotic fluid prior to 34 weeks' gestation, meconium aspiration chiefly affects infants at term and postterm.
Epidemiology Incidence : In developing countries with less availability of prenatal care and where home births are common, incidence of meconium aspiration syndrome is thought to be higher and is associated with a greater mortality rate.
Epidemiology cont.. Mortality/Morbidity : The mortality rate for meconium aspiration syndrome resulting from severe parenchymal pulmonary disease and pulmonary hypertension is as high as 20%. Other complications include air leak syndromes (eg, pneumothorax, pneumomediastinum, pneumopericardium) which occur in 10-30% of infants with meconium aspiration syndrome.
Pathophysiology fetal hypoxic stress in utero meconium passage results from neural stimulation of a mature GI tract and usually results from fetal hypoxic stress. As the fetus approaches term, the GI tract matures, and vagal stimulation from head or cord compression may cause peristalsis and relaxation of the rectal sphincter leading to meconium passage.
Conti.. Meconium directly alters the amniotic fluid, reducing antibacterial activity and subsequently increasing the risk of perinatal bacterial infection. Additionally, meconium is irritating to fetal skin, thus increasing the incidence of erythema toxicum.
However, the most severe complication of meconium passage in utero is aspiration of stained amniotic fluid before, during, and after birth. Aspiration induces hypoxia via 4 major pulmonary effects: 1 - airway obstruction 2 - surfactant dysfunction 3 - chemical pneumonitis 4 - pulmonary hypertension
1- Airway obstruction Complete obstruction of the airways by meconium results in atelectasis. Partial obstruction causes air trapping and hyperdistention of the alveoli, commonly termed the ball-valve effect. The gas that is trapped (hyperinflating the lung) may rupture into : 1- the pleura ( pneumothorax ), 2- mediastinum ( pneumomediastinum ), or 3- pericardium ( pneumopericardium ).
2- Surfactant dysfunction Meconium deactivates surfactant and may also inhibit surfactant synthesis.
3- Chemical pneumonitis Enzymes, bile salts, and fats in meconium irritate the airways and parenchyma, causing a release of cytokines (including tumor necrosis factor (TNF)-α, interleukin (IL)-1ß, I-L6, IL-8, IL-13) and resulting in a diffuse pneumonitis that may begin within a few hours of aspiration.
4- Persistent pulmonary hypertension of the newborn (PPHN) as a result of chronic in utero stress and thickening of the pulmonary vessels. PPHN further contributes to the hypoxemia caused by meconium aspiration syndrome.
although meconium is sterile, its presence in the air passages can predispose the infant to pulmonary infection.
Presence of meconium in amniotic fluid is required to cause meconium aspiration syndrome (MAS), but not all neonates with meconium-stained fluid develop meconium aspiration syndrome
Inadequate removal of meconium from the airway prior to the first breath and use of positive pressure ventilation (PPV) prior to clearing the airway of meconium increase the likelihood of a neonate developing meconium aspiration syndrome.
Green urine may be observed in newborns with meconium aspiration syndrome less than 24 hours after birth.
Meconium pigments can be absorbed by the lung and can be excreted in urine.
Physical examination : Severe respiratory distress may be present. - Symptoms include the following: * Cyanosis * End-expiratory grunting * Alar flaring * Intercostal retractions * Tachypnea - Barrel chest in the presence of air trapping - Auscultated rales and rhonchi (in some cases) - Yellow-green staining of fingernails, umbilical cord, and skin may be observed.
Objectives : Definition of MAS Background Epidemiology Pathophysiology How MAS induce hypoxia ? Remember Physical examination. Air leak syndromes - pulmonary interstitial emphysema, - pneumomediastinum, - pneumothorax, - pneumopericardium, - pneumoperitoneum, and
Air leak syndrome Air-leak syndromes include : - pulmonary interstitial emphysema, - pneumomediastinum, - pneumothorax, - pneumopericardium, - pneumoperitoneum, and - subcutaneous emphysema. Pneumothorax and pneumomediastinum occur in 1 to 2% of normal neonates. Pulmonary air-leak syndromes involve dissection of air out of the normal pulmonary airspaces.
Air leak is more common and severe among neonates with lung disease, who are at risk because of : poor lung compliance and the need for high airway pressures poor lung compliance and the need for high airway pressures (eg, in respiratory distress air trapping air trapping (eg, meconium aspiration syndrome), which leads to alveolar overdistention.
Diagnosis of air leak syndrome ( in general) Many affected neonates are asymptomatic. diagnosis is suspected clinically or because of deterioration in O 2 status and is confirmed by x-ray.
Treatment ( in general ) Treatment varies by type of air leak but in ventilated infants always involves lowering inspiratory pressures to lowest tolerated settings. High-frequency ventilators may be helpful but are of unproven benefit.
Pulmonary interstitial emphysema ( PIE ) is leakage of air from alveoli into the pulmonary interstitium, lymphatics, or subpleural space. It usually occurs in infants with poor lung compliance, such as those with respiratory distress syndrome who are being treated with mechanical ventilation, but it may occur spontaneously.
PIE Conti.. One or both lungs may be involved, and pathology may be focal or generalized within each lung. If dissection of air is widespread, respiratory status may acutely worsen because lung compliance suddenly is reduced.
Dx. Of PIE Chest x-ray shows a variable number of cystic or linear lucencies in the lung fields.
This radiograph, obtained from a 1-day-old premature infant at 24 weeks' gestation, shows bilateral pulmonary interstitial emphysema (PIE). Linear radiolucencies extending up to the lung periphery are visible.
Treatment Pulmonary interstitial emphysema may resolve dramatically over 1 or 2 days or persist on x-ray for weeks. Treatment is mainly supportive. If one lung is significantly more involved than the other, the infant may be laid down on the side of the lung with the more severe pulmonary interstitial emphysema; this will help to compress the lung with pulmonary interstitial emphysema, thereby decreasing air leakage and perhaps improving ventilation of the normal (elevated) lung.
Pneumomediastinum Pneumomediastinum is dissection of air into connective tissue of the mediastinum, the air may further dissect into the subcutaneous tissues of the neck and scalp. Pneumomediastinum usually causes no symptoms or signs, though subcutaneous air causes crepitus. No treatment is usually needed, and the condition resolves spontaneously.
This initial radiograph obtained shortly after birth shows patchy, coarse parenchymal opacities and severe hyperexpansion. In addition, pneumomediastinum is present on the right (arrows), outlining the right lobe of the thymus (T).
Pneumopericardium Pneumopericardium is dissection of air into the pericardial sac. It affects mechanically ventilated infants almost exclusively. Most cases are asymptomatic, but if sufficient air accumulates, it can cause cardiac tamponade. Treatment is pericardiocentesis followed by surgical insertion of a pericardial tube.
Pneumoperitoneum Pneumoperitoneum is dissection of air into the peritoneum. Diagnosis is made by abdominal x-ray and physical examination. clinical symptoms that include abdominal rigidity, absent bowel sounds, and signs of sepsis suggest abdominal viscus injury.
Pneumothorax Pneumothorax is the collection of air or gas in the space inside the chest around the lungs, which leads to a lung collapse. The most common cause of pneumothorax is respiratory distress syndrome, which occurs in premature babies. respiratory distress syndrome MAS is another cause of pneumothorax in newborn Pneumothorax is more common in boys than girls.
C/P Many infants with pneumothorax are asymptomatic. The symptoms include ( sgins of respiratory distress ) cyanosis Tachypnia Flaring ala nasi Grunting with breathing Irritability Restlessness Retractions of accessory muscles of respiration.
Dx. Diagnosis is confirmed by chest x-ray or, in the case of tension pneumothorax, return of air during thoracentesis.
Chest radiograph of a full-term infant with meconium aspiration showing coarse interstitial infiltrates and left pneumothorax
Treatment : Most small pneumothoraces resolve spontaneously, but larger and tension pneumothoraces require evacuation of the air in the pleural cavity. In tension pneumothorax, a scalp vein needle or an angiocatheter and syringe can be used to temporarily evacuate free air from the pleural space. Definitive treatment is insertion of an 8 or 10 French chest tube attached to continuous suction. Follow-up auscultation, transillumination, and x-ray confirm that the tube is functioning properly.