Meconium aspiration syndrome

meconium aspiration syndrome

1. RAKHI DAS I YR MSc NURSING, JMCON, THRISSUR

2. Introduction Meconium aspiration syndrome (MAS) is one of the most common causes of severe respiratory failure in term and post term infants caused by inhalation of meconium before, during or immediately after delivery. It may be present with varying degrees of severity, ranging from mild respiratory compromise to severe forms that may result in perinatal death.

3. Incidence In western countries, MSAF incidence rate is reported to range from 5.6 to 24.6% and MAS develops in 35.8% infants born through MSAF An Indian study from Maharashtra 2000, found MSAF 16.5 with MAS developing in 18.7% live birth. Other studies reported evident increase in the incidence.

4. Definition Cleary & Wiswell ; Respiratory distress in infant born through meconium stained amniotic fluid whose symptoms cannot be otherwise explained. National neonatal- perinatal database of India; MAS should be diagnosed if any two of the following three criteria are present Meconium staining of liquor or straining of umbilical cord or skin or nails Respiratory distress soon after birth within one hour Radiological evidence of aspiration pneumonitis

5. Meconium pathogenesis Meconium is a viscous, dark green substance which has bile, lanugo , shed intestinal epithelial cells and water. Intrauterine distress causes passage of meconium into amniotic fluid. Liquor can be aspirated into the lungs during labour and delivery.

6. Mechanism of passage of meconium There are two controls operating the fetal meconium passage: Hormonal control dependent upon " motilin "- intestinal peptide responsible for bowel peristalsis and defecation Neural control dependent upon maturation and myelination of neural plexus of gastrointestinal tract In utero passage of meconium is commonly not occurring before 34 weeks of gestation because of Relative lack of strong peristalsis Good anal sphincter tone Present of a "cap" of particularly viscous meconium in rectum

7. Risk factors Fetal distress associated with fetal asphyxia and decreased umbilical venous blood PO2 Compression of umbilical cord eg : Olivgohydramnias Gut maturation in post term neonates Breech presentation and pressure over buttocks Listeriosis (representing fetal diarrhoea )

8. Classification of meconium passage Based on timing Early - noted on rupture of fetal membranes prior to, or during active stage of labour Late - MSAF passed in second stage of labour after clear fluid noted previously Based on content consistency Light meconium - lightly stained amniotic fluid, yellow or greenish colour Heavy meconium - darkly stained amniotic fluid, dark green or black in colour, usually thick and tenacious

9. Clinical features General appearance Baby usually term for post term Classic signs of postmaturity include dry and loose or peeling skin, overgrown nails, abundant scalp hair, visible palmar and sole crease, minimal fat deposits, green/ brown/ yellow colouring of skin from meconium staining

10. Clinical features contd … Respiratory features Tachypnea more than 120 beats per minute Marked sternal retraction Intercostal and subcostal recession Use of accessory muscles and flaring of nostrils Expiratory grunting maybe present Widespread crepitus and ronchi Air trapping due to Ball - valve effect Overdistension of chest with increased AP diameter Apnea in neurological involvement

11. Clinical features contd … Cardiovascular features In absence of asphyxial damage to myocardium, no specific cardiovascular features Myocardial damage manifest as hypotension or CHF If persistant pulmonary hypertension (PPHN), s2 may remain single along with Murmur of tricuspid Incompetence

12. Clinical features contd … Abdominal features Downward displacement of the diagram due to air trapping resulting in palpable liver and spleen In severe cases bowel sounds are absent and no further meconium may be passed If neurological involvement is there urinary retention makes bladder palpable

13. Clinical features contd … Central nervous system features Baby may be normal neurologically or may have features of Birth asphyxia which may vary from stage I to III hypoxemic ischemic encephalopathy (HIE)

14. Diagnostic evaluation History collection (antenatal history, gestational score, obstructive history, onset of labour , correct date of expected delivery, previous history in the family) Physical findings ( meconium stained amniotic fluid during first stage of labour , fetal distress or decrease movement at term, radiological changes and presence of meconium in trachea, staining of skin, nails or umbilical cord immediately after birth

15. Investigations - hematological changes (increased WBC, thrombocytopenia in PPHN, DIC secondary to severe birth asphyxia Chemical changes (decreased PO2, increased PCO2, pH changes) Urine analysis - usually normal output unless renal failure develops, greenish brown colour of urine due to absorbed meconium pigments across pulmonary epithelium and excretion

16. Electrocardiography or echocardiography Normal in uncomplicated cases, sub- endocardial ischemia in severe intrapartum asphyxia, reduced cardiac contractility Chest X Ray Helps in determining extent of intrathoracic Pathology Identify areas of atelectasis or air block syndromes Patchy infiltrate, coarse streaking of lung field, increased AP diameter, atelectasis , flat diaphragm, plural effusion, pneumothorax , pneumonitis

17. Management Initial management Observe closely for respiratory distress Monitor oxygen saturation Immediate neonatal resuscitation Avoid hypoxemia

18. Routine care Maintain hydration High flow oxygen to prevent hypoxia Peripheral perfusion to be maintained with ionotopic agents Chest physiotherapy and oropharyngeal suctioning as-needed Correction of metabolic acidosis monitoring of renal function of chemical pneumonitis and potential benefits Broad spectrum Antibiotics

19. Thermal environment Conservation of heat, warmer care Cling wrap to prevent heat loss to environment Minimal handling and disturbance to baby and provide sensory comfort Acid-base hemostasis Maintenance of PaO2 and PaCO2 monitor O2 saturation and provide adequate concentration of warmed humidified oxygen 80 to 90%

20. Ventilatory support Continuous positive Airway pressure (CPAP) Intermittent positive pressure ventilation (IPPV) rate of 60 to 80 per minute and low levels of PEEP Drug therapy Glucocorticoid - for treatment Broad spectrum antibiotics

21. Surfactant replacement therapy Intratracheal administration of surfactant ( Colfosceril Palmitate 108mg as lyphilised powder and supply with cetyl alcohol, tyloxapol and sodium chloride 5ml/kg body weight; no more than 3 doses Rescue treatment should be administered in two doses. Initial dose as soon as possible after diagnosis of respiratory distress syndrome. Saline lavage of surfactant Replacement and surfactant lavage with or without subsequent bolus to 'wash out' meconium in the Airways

22. Other management High frequency ventilation of high frequency nasal cannula (HFNC) Extracorporeal membrane oxygenation(ECMO)