syndrome

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syndrome

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• mekonionarion opium like (Aristotle)
• Meconium stained amniotic fluid 8-15 of all
  deliveries.
• 5 of them meconium aspiration syndrome
• 5 mortality

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Origin and composition

• Meconium is recognized 70-85 d of gestation
• Composition
• Water, Mucopolysaccharides, Cholesterol and
  sterol precursos, Protein, Lipid, Bile acids and
  salts, Enzymes, Blood group substances, Squamous
  cell, Vernix caseosa
• No bacteria!

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In utero passage

• Risk factors associated with in utero passage of
  meconium
• Postterm pregnancy
• Little/no amniotic fluid at amniotomy
• Oligohydramnion by US
• IUGR/ placental insufficiency
• Maternal HTN
• Preeclampsia
• Maternal drug abuse (tobacco, cocaine).
• Gestational age gt 34w increasingly present with
  advancing gestational age.

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Pathophysiology

• As the GI tract matures
• vagal stimulation ? peristalsis rectal
  sphincter relaxation ? meconium
• Etiology not well understood
• Fetal response to intra-uterine stress hypoxia ?
  increased vagal tone
• Transient compression of umbilical cord/head ?
  increased vagal tone
• Maturation of of fetal intestinal function

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Timing of the initial insult

• Traditional belief immediately after birth
• Several investigations Most cases occur in utero
  when fetal gasping is initiated before delivery.

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Effects of meconium

• Reduce antibacterial activity (perinatal
  bacterial infection)
• Irritating to fetal skin ( erythema toxicum)
• The most severe complication of meconium passage
  in utrro is aspiration of stained amniotic fluid
  before, during, and after birth

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Meconium aspiration syndrome - pathophysiology

• Airway obstruction
• Chemical pneumonitis
• Surfactant dysfunction
• Umbilical vessel damage
• Persistent pulmonary hypertension of the newborn

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Airway obstruction

• Immediate obstruction of large airways (volume
  dependent )
• hypoventilation gt hypoxemia, hypercapnea,
  acidosis
• Central clearing obstruction of small airways
• Complete ? athelectasis
• Partial ? air trapping (ball valve phenomenon) ?
  hyperdistention of alveoli ? increaesed lung
  resistance during exhalation
• pneumothorax, pneumomediastinum ,
  pneumopericardium.

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Chemical pneummonitis

• 50 of cases
• Enzemes, bile salts, fats irritants? PMN, MQ,
  inflammatory mediators.
• Chemical pneumonitis, edema (6h) ? inflamation
  (24h)
• Hyalin membranes, hemorrhage, vascular necrosis
  can occur.
• Bacterial superinfection.
• Activated Vasoactive mediators play a role in the
  develipment of PPHN.

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Surfactant dysfunction

• Free fatty acids (paimitic, stearic, oleic)
  higher minimal surface tention than surfactant
  (striping effect)
• decreased lung compliance
• concentration dependent

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Umbilical vessel damage

• Umbilical vessels exposed to meconium ? may cause
  severe focal inflammation injury.
• Spasm and necrosis ? fetal hypoperfusion
• 1 meconium induced umbilical vascular necrosis
  among meconium stained placentas.

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Persistent pulmonary hypertension of the newborn

• Final common pathway for the severe morbidity and
  mortality in infants with MAS.
• Hypoxia ? Pulmonary arterial vasoconstriction.
• Abnormal pulmonary arterial muscularization ? m/p
  chronic change
• Association between MAS and PPHN
• Direct pathogenic cause of lung damage
• Simple marker of chronic intrauterine hypoxia

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Risk factors of MAS developing into PPHN

• Risk factors of meconium aspiration syndrome
  developing into persistent pulmonary hypertension
  of newborn.Acta Paediatr Taiwan. 2004
  Jul-Aug45(4)203-7 362 cases of MAS (17 with
  PPHN).
• Pneumothorax, change in FHR base line, asphyxia ?
  most important risk factors

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Risk and severety of MAS

• Degree of contamination of the amniotic fluid and
  Presence of meconium in the airway at delivery ?
  is meconium itself a direct primary cause of
  morbidity mortality?
• MAS is commonly associated with chronic hypoxia?
  is meconium a marker of fetal maturation of
  chronic fetal hypoxia?
• Asphyxia, pneumothorax, PPHN the most important
  risk factors of mortality in MAS.

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Clinical presentation

• Depressed at birth
• Early onset of respiratory distress (within 2 h)
• Mild tachypnea
• cyanosis
• Dyspnea granting, ala nazi, intercostal
  retraction
• Barral chest (presence of air trapping)
• respiratory failure
• Auscultayion wet inspiratory crackles,
  occasional expiratory noises
• Severe Mas
• Hypoxemia R?L shant
• Persistant fetal circulation
• PPHN hypoxic pulmonary arterial
  vasoconstriction acidosis, hypercapnea,
  hypoxemia (prenatal perinatal maladaptation)
• Cardiopulmonary failure
• acidosis

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Complication

• PPHN
• AIR LEAK
• PULMONARY HEMORRAGE
• ASPHYXIA COMPLICATIONS

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Laboratory

• Hypoxemia (R?L shunt)
• Hypercarbia (in significant obstruction)
• Respiratory alkalosis (hyperventilation)
• Combined respiratory and metabolic acidosis
  (severe disease respiratory failure)

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Chest x-ray

• 73 - positive x-ray findings
• Global atelectasis early
• Patchy dense opacifications (decreased
  vantilation) accompanied by areas of
  hyperinflation
• Widespread infiltrates
• Consolidations
• Small pleural effusion (30)
• Pneumothorax/ pneumomediastinum (25)

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Prenatal diagnosis and prevention

• Diagnosis of fetus at risk monitoring fetal
  status.
• Thick VS thin meconium
• Meconium and FHR abnormalities
• Amnioinfusion during labor
• Nasopharyngeal suctioning

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Upon delivery intervention

• combined approach nasopharengeal suctioning
  neonatal trachea suction.
• Thick meconium depressed infant ? tracheal
  suction - marked reduction in morbidity and
  mortality.
• The American Academy of pediatrics Neonatal
  Resuscitation Program Steering Guidelines

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management

• Minimize agitation (prevent additional acidosis
  and hypoxemia) optimal thermal environment,
  minimal handling, muscle relaxation.
• NGT
• Respiratory care
• Maintain systemic blood pressure (R?L shunt)
• Antibiotics.

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MAS treatment ventilation support

• Main target oxigenation! PaO2 60-90mmHg
• difficulty with oxigenation? positive airway
  pressure (CPAP) improves ventilation,
  stabilizes small airways.
• Respiratory acidosis/severe respiratory distress
  ? mechanical ventilation sPO2gt 50 mm Hg with
  FiO2 100 pHlt 7.2 . sedation! Relaxation!
• Surfactant
• iNO
• failed conventional ventilation HFJV, HFO
• ECMO

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SURFACTANT

• Lung lavage using sufractant in MAS is currently
  being investigated
• Treatment of severe meconium aspiration syndrome
  with porcine surfactant a multicentre,
  randomized, controlled trialActa Paediatr. 2005
  Jul94(7)896-902.
• Pulmonary function after surfactant lung lavage
  followed by surfactant administration in infants
  with severe meconium aspiration syndrome.J
  Matern Fetal Neonatal Med. 2004 Aug16(2)125-30.
  

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Steroids

• Pathophysiology anti-infalammatory properties.
• Corticosteroid treatment, started early, show
  some improvement in oxigenation and pulmonary
  hemodynamics durind acute phase.
• Effect on morbidity and mortality ? Cochrane
  Database Syst Rev, 2003 ? insufficient evidence.
• Further research clinucal significant, optimal
  timing, dosing.

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