MECONIUM ASPIRATION SYNDROME

I. General

  1. Mec is mostly bile salts & epithelial cells
  2. 8-20% of all deliveries have mec staining of amniotic fluid
  1. Passage of mec us. occurs in SGA or post-term
  2. Almost never occurs before 34 weeks
  3. Mec is passed more easily (i.e. with less hypoxic insult) in post-term than f/t fetuses

II. Pathophysiology

  1. Not all mec passage is pathologic: can be due to vagal stim. from transient cord compr.
  2. In normal kids, reflex closing of glottis prevents aspiration
  3. Mec aspiration sd. (MAS) and its risk factors
  1. Occurs in about 6-10% of neonates exposed to mec-stained amniotic fluid
  2. More common with oligo & perinatal asphyxia
  3. Thick or mec-stained amniotic fluid definitely ass?d with higher incidence of MAS
  4. Risk for MAS is least when mec is seen not at ROM but later in labor
  1. May also increase mom's risk of postpartum endometritis

III. Clinical features

  1. Complications of MAS: peripheral & proximal airway occlusion; intrapulmonary shunting; cor pulmonale; pneumothorax; pneumonitis; acidosis; persistent fetal circulation
  2. Can present:
  1. At birth with neonatal depression
  2. 1-2h of age with respiratory distress (can occur as late as 24h of age)
  1. Tachypnea, grunting, flaring, retracting, cyanosis
  2. Prolonged exp. phase & barrel-shaped chect from air trapping
  3. May be confused with transient tachypnea of newborn
  1. CXR shows overexpansion, coarse irregular densities, patchy atelectasis
  1. May lag behind clinical severity
  2. 20-50% get PTX
  1. Hypoxemia, hypercapnia, resp. acidosis can occur

IV. Clinical management

  1. During labor and at delivery--see also Neonatal Resuscitation
  1. Recognize risk factors: post-dates, oligo, fetal distress
  2. Amnioinfusion (variable views on indications) to dilute the mec
  3. Controlled delivery of head with suction of upper airway before delivery of chest
  1. In a randomized trial of 2094 full-term infants, vigorous at birth (defined as HR > 100, spontaneous respirations, and "reasonable tone," i.e. spontaneous movements or "some degree of extremity flexion"--degree of vigor assessed within the first 10-15 sec after delivery), with mec noted during labor, randomized to intubation & intratracheal suctioning vs. "expectant therapy"; there was no difference in MAS incidence or incidence of other respiratory disorders, including in the subgroup with thick mec; intubation babies sig. more likely to have 1-minute Apgars < 7 (17% vs. 6%) (Peds 105:1, 2000)
  2. 2,514 full-term newborns with meconium-stained amniotic fluid randomized to suctioning of oropharynx & nasopharynx before delivery of shoulders (vs. no suctioning); no sig. diff. in incidence of MAS (4% in both groups), or incidence of severe MAS, overall mortality, length of hospital stay, or need for O2 tx or mechanical ventilation (Lancet 364:597, 2004--JW)
  1. Post-delivery: Rapidly hand baby to Peds for visualization of cords & intubation prior to first breath or any positive pressure ventilation
  1. Preferred method is intubation with 3.0 or 3.5 tube (larger is better) attached to meconium aspirator & wall suction at 80-100 mmHg
  1. Alternative is suction catheter in ET tube (us. too small for effective suction)
  2. Last resort is mouth suction to ET tube
  1. Assistant should be checking baby's heart rate
  2. If severely depressed infant & you're not skilled in rapid intubation, need for resuscitation takes priority
  3. With meconium in trachea, repeated visualization/intubation with chest PT may be beneficial
  4. Risks of laryngoscopy: 2% get intubation, & tracheal suctioning: physical injury, apnea, arrhythmias, epiglottitis
  5. Put on 100%O2, CR monitor, check VS, HCT, glucose, ABG, CXR
  6. Neonatology consultation with further intervention PRN
  1. Some may need ventilator support or ECMO