Meconum aspiration syndrome

Meconum aspiration syndrome is one of the common cause of respiratory distress of newborn

1. WELCOME TO SEMINAR

2. PRESENTED BY- DR. SYED KAMRUL HASAN IMO, DEPARTMENT OF NICU SWMCH, SYLHET Meconium Aspiration Syndrome (MAS)

3. Definition : Aspiration of meconium contaminated aminotic fluid by a fetus, or a term or post term newborn during birth is termed as meconium aspiration. The typical clinical manifestations produced by the meconium aspiration pneumonia is termed as meconium aspiration syndrome.

4. Epidemiology Meconium Stain Amniotic Fluid observed in (8-20)% of all births. The incidence of MSAF increase from 1.6% at 34-37 weeks to 30% at > 42 weeks Meconium Aspiration Syndrome occurs in 5% of newborns delivered through MSAF. MAS primarily affects Term or Post-term Infants.

5. Composition of meconium : Meconium is the first intestinal discharge of the newborn infants. Which is greenish black in colour & contains: Water (75%) Mucopolysaccharides Proteins Cholesterol, lipids Bile acids & salts Enzymes Vernix & squamous cells

6. Cause of MSAF : Fetal maturation : Usually term or post term (high motilin level) Vagal stimulation by cord or head compression in absence of fetal distress. In utero stress (hypoxia, acidosis) producing relaxation of anal sphincter.

7. Risk factors for MAS : Maternal risk factor includes all which induce fetal distress & hypoxia : Maternal Hypertension Maternal DM Maternal chronic respiratory or Cardiovascular disease Maternal infection Maternal drug use

8. Placental insufficiency Post term pregnancy Pre- eclampsia / eclampsia Oligohydramnios IUGR Abnormal fetal heart rate pattern

9. Pathophysiology Fetal meconium passage depends on hormonal & parasympathetic neural maturation. Fetal distress & vagal stimulation are 2 probable factors may stimulate intestinal peristalsis & relaxation of the anal sphincter to causes passage of meconium into the amniotic fluid leads to MSAF. Gasping by the fetus or newborn infants can cause aspiration of aminotic fluid contaminated with meconium and causes the following :

10. Mechanical obstruction of airways : Thick and viscous meconium lead to Complete or partial airway obstruction. With onset of respiration meconium migrates from central to peripheral airways. Complete obstruction may leads to atelectasis resulting in hypoxia & increase PVR. Partial obstruction may result in a Ball-valve phenomenon leading to air trapping & alveolar hyperexpansion . Increase risk of pneumothorax 15 – 33%.

11. Chemical pneumonitis : with distal progressing of meconium chemical pneumonitis develop resulting bronchiolar edema and narrowing of the small airways, all leading to increase hypercarbia & hypoxemia. Surfactant inactivation: Bilirubin , fattyacid , triglycerides, cholesterol content of meconium due to their higher surface tension, leads to surfactant dysfunction by stripping surfactant from the surface of the alveoli.

12. Pulmonary hypertension: meconium in lungs stimulate release of pro inflammatory cytokines and vasoactive substance which cause pulmonary vasoconstriction. Also hypoxia, acidosis, and hyperinflation contribute to pulmonary hypertension. The increase in pulmonary vescular resistant may lead to atrial & ductal right to left shunting.

13. Pathophysiology of MAS

14. CLINICAL FEATURES : History : Infants with MAS must have a history of MSAF. They often are Term or post-term Have a history of fetal distress Have a low APGAR score at birth Many are depressed at birth.

15. Physical examination : Infants with MAS often exhibit signs of postmaturity : peeling skin, long fingernails, abundant hair and decreased vernix . Affected patients typically have respiratory distress with marked tachypnea and cyanosis. Use of accessory muscles of respiration are evidenced by intercostal and subcostal retractions and abdominal (paradoxical) breathing, often with grunting and nasal flaring.

16. The skin, umbilical cord, and nails may be meconium -stained, depending upon how long the infant has been exposed to meconium & concentration of meconium . Umbilical cord begin to stain after 15 minute exposure to thick MSAF or 1 hour to lightly stained fluid. Nails will become stained after 4-6 hours vernix after 12 to 14 hours of exposure .

17. Umbilical cord stained with meconium

18. Significant perinatal asphyxia, poor respiratory effort, decrease muscle tone. The chest typically appears barrel-shaped, with an increased anterior-posterior diameter caused by hyperinflation. Auscultation reveals fine crepitations with rhonchi and reduced air entry immediately after birth.

19. Some patients are asymptomatic at birth and develop worsening signs of respiratory distress as the meconium moves from the large airways into the lower tracheobronchial tree. Most infants who develop symptoms will do so in the first 12 hours of life.

20. Differential Diagnosis : Perinatal Asphyxia Respiratory Distress Syndrome Transient Tachypnea Of Newborn Congenital Pneumonia Congenital Heart Disease

21. PNA RDS T TN / Wet Lungs CHD Congenital Pneumonia H/O delayed crying after birth or no cry Pale Gasping respiration or no respiration Bradycardia Hypotonia Convulsion Shock Immediate resuscitation & Post resuscitation management Respiratory distress with in 1 hr of life Due to deficiency of surfactant H/O preterm delivery, IDM, C/S CXR : ground glass appearance, air bronchogram , complete white out lungs. Specific treatment give surfactant. Mild self limited pulmonary disorder Due to delayed absorption of fetal lung fluid More in cesarean delivery CXR : Prominent vascular markings, fluid in the interlobar fissure, flat diaphragm Improve by 12-24 hours Respiratory distress with or without cyanosis Murmur on auscultation CXR : Cardiomegaly Echo. With color doppler is diagnostic Mother has a blood stream infection Mother may be febrile or have other sign of infection Crepitation on Auscultation CXR : Homogeneous or patchy opacity, pneumatocele , pleural effusion Treat with broad spectrum antibiotic

22. Diagnosis : MAS must be considered in any infant born through MSAF who develops symptoms of RD with typical chest x ray findings A chest radiographs shows hyperinflation of the lung field and flatten diaphragms. There are coarse irregular patchy infiltrates A pneumothorax and pneumomediastinum may be present .

23. Coarse irregular patchy infiltrate with emphysema

24. Areas of opacification due to atelectasis

25. CXR from an infant with severe MAS showing bilateral patchy areas of increased density

26. Arterial blood gas measurements typically show hypoxemia and hypercarbia.In mild cases hyperventilation may result in respiratory alkalosis. Infants with sever disease usually have a respiratory acidosis due to airway obstruction, atelectasis & pneumonitis . Echocardiography : Infants with pulmonary hypertension and right-to-left atrial & ductal shunt is frequently associated finding in infants with MAS.

27. Complication Chemical Pneumonitis Emphysema Pneumothorax Persistent pulmonary hypertension Respiratory failure

28. Development of a left pneumothorax in an infant with MAS

29. Management : Prevention : Prevention of passage of meconium in utero : Identification of high risk pregnancies and close monitoring. Pregnancy that continue past due date, induction as early as 41 weeks may help prevent meconium aspiration. If there is sign of fetal distress corrective measure should be undertaken or infant should be delivered in timely manner.

30. Transcervical amnioinfusion with normal saline solution in case of thick meconium & oligohydramnios may reduce the incidence of fetal distress & meconium aspiration.

31. Prevention of meconium aspiration : Baby born through thick particulate mecomium : At delivery suction the oropharynx before the shoulders are delivered. Intubation & suction under direct laryngoscopy is mandatory before triggering the first breath by drying & stimulating the infant. Intubation & suction should be continued until the meconium has been cleared. Baby born through thin meconium : suction of the mouth first who have effective respiration at the time of delivery.

32. Treatment Apparently well child born through MSAF, most of them do not require any interventions besides close monitoring for respiratory distress. Some may be depressed at birth & require resuscitation. Oxygen by mask should be administered as soon as the trachea has been cleared. Oropharyngeal suction should be provided to assist pulmonary toileting.

33. Broad spectrum antibiotic should be started if a radiological infiltrate or documented infection. Monitor temperature , blood gas level, fluid & electrolyte balance. Hypoxia & acidosis may lead to persistent pulmonary hypertension & should be treated promptly. Mechanical ventilation may be required. Those who fail to improve conventional treatment may benefit from surfactant therapy, nitrous oxide or ECMO.

34. Approach to the ill newborns: Transfer to NICU. Monitor closely. Full range of respiratory support should be given .

35. Treatment in NICU Goals: Increased oxygenation while minimizing the barotrauma (may lead to air leak). Prevent pulmonary hypertension . Prevent secondary infection.

36. Ventilatory support depends on the amount of respiratory distress: O2 hood Continuous positive airway pressure (CPAP) Mechanical ventilation : High-frequency ventilation (HFV) should reduce air leaks & may slow the progression of meconium down the tracheobronchial tree and allow more time for meconium removal.

37. Surfactant therapy Surfactant therapy in MAS showed promising results with decrease in the number of infants requiring ECMO and Possible reduction of pneumothorax .

38. Inhaled Nitric oxide (NO) Selective pulmonary vasodilation . Activate guanylate cyclase and increases cyclic GMP and acting directly on the vascular smooth muscle. Use of iNO reduces the need for ECMO by 40%. Pretreatment with surfactant improves in delivery of inhaled NO to the alveoli.

39. Extracorporal membrane oxygenation( ECMO) ECMO is a form of cardiopulmonary bypass that augments systemic perfusion & provide gas exchange. Most common venoarterial bypass, which required carotid artery ligation & placement of large catheter in the right internal jugular vein & carotid artery.

40. ECMO works by removing blood from the person’s body & artificially removing the CO2 & oxygenating RBC.

41. ECMO required complete heparinization to prevent clotting in the circuit, so can’t be use in patient with or at risk of IVH. 40% of infants with MAS treated with inhaled NO fail to respond and require ECMO. 35% of ECMO patients are with MAS. Survival rate after ECMO 93-100%.

42. Progonosis : Infants of MAS who do not require ventilation recover within 7- 10 days. Mortality reduced to <5% with new modalities of therapy such as administration of surfactant, HFV, iNO , ECMO. Chronic lung disease may result from prolong mechanical ventilation Those with significant asphyxia insult may demonstrate neurologic sequele .

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