Medical Care
The American College of Obstetricians and Gynecologists (ACOG) continues to provide guidance regarding the appropriate indications for delivery to prevent neonatal complications of a prolonged pregnancy, as well as for avoiding the unnecessary delivery of a preterm baby. [16, 17]
In patients with meconium aspiration syndrome (MAS), a thorough cardiac examination and echocardiography are necessary to evaluate for congenital heart disease and persistent pulmonary hypertension of the newborn (PPHN).
Quantifying the degree of pulmonary hypertension, prior to instituting therapy, is essential.
Prevention of MAS
Prevention of MAS is paramount. Obstetricians should closely monitor fetal status in an attempt to identify fetal distress.
When meconium is detected, amnioinfusion with warm, sterile saline is theoretically beneficial to dilute the meconium in the amniotic fluid, thereby minimizing the severity of the aspiration. Whether amnioinfusion is beneficial in practice remains debatable. Several studies have concluded that the evidence does not support routine amnioinfusion to prevent MAS. [18, 19, 20] One large, multicenter study determined that amnioinfusion did not reduce the risk of moderate or severe MAS or MAS-related death. [21] However, a recent meta-analysis favors amnioinfusion to prevent MAS and their data found that amnioinfusion has helped reduce the incidence of MAS by 67%. [22]
As noted earlier in the Presentation section, current recommendations no longer advise routine intrapartum suctioning for infants born to mothers with meconium staining of the amniotic fluid. [10, 11, 23, 24, 25]
No clinical trials justify suctioning on the basis of the meconium consistency. Do NOT perform the following harmful techniques in an attempt to prevent aspiration of meconium-stained amniotic fluid:
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Squeezing the chest of the baby
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Inserting a finger into the mouth of the baby
The American Academy of Pediatrics (AAP) Neonatal Resuscitation Program Steering Committee and the American Heart Association (AHA) have promulgated guidelines for management of babies exposed to meconium. [10] The guidelines are under continuous review and are revised as new evidence-based research becomes available. The seventh edition of the Neonatal Resuscitation Program modified its previous recommendations regarding endotracheal suctioning for the nonvigorous infant. The most recent guidelines are as follows [10, 11] :
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If the baby is vigorous (defined as having a normal respiratory effort and normal muscle tone), the baby may stay with the mother to receive the initial steps of newborn care. A bulb syringe can be used to gently clear secretions from the nose and mouth.
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If the baby is not vigorous (defined as having a depressed respiratory effort or poor muscle tone), place the baby on a radiant warmer, clear the secretions with a bulb syringe, and proceed with the normal steps of newborn resuscitation (ie, warming, repositioning the head, drying, and stimulating). If, after these initial steps are taken, the baby is still not breathing or the heart rate is below 100 beats per minute (bpm), administer positive pressure ventilation.
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Resuscitation should follow the same principles for infants with meconium-stained fluid as for those with clear fluid.
Continued care in the neonatal intensive care unit (NICU)
Maintain an optimal thermal environment to minimize oxygen consumption.
Minimal handling is essential because these infants are easily agitated. Agitation can increase pulmonary hypertension and right-to-left shunting, leading to additional hypoxia and acidosis. Sedation may be necessary to reduce agitation.
An umbilical artery catheter should be inserted to monitor blood pH and blood gases without agitating the infant.
Continued respiratory care includes oxygen therapy via hood or positive pressure, and it is crucial in maintaining adequate arterial oxygenation. Mechanical ventilation is required by approximately 30% of infants with MAS. [4] Make concerted efforts to minimize the mean airway pressure and to use as short an inspiratory time as possible. Oxygen saturations should be maintained at 90-95%.
Surfactant therapy is commonly used to replace displaced or inactivated surfactant and as a detergent to remove meconium. [26, 27, 28] Although surfactant use does not appear to affect mortality rates, it may reduce the severity of disease, progression to extracorporeal membrane oxygenation (ECMO) utilization, [29] and decrease the length of hospital stay.
Although conventional ventilation is commonly used as initial management, high-frequency oscillation and jet ventilation are alternative effective therapies. Hyperventilation to induce hypocapnia and compensate for metabolic acidosis is no longer a primary therapy for pulmonary hypertension, because hypocarbia often results in decreased cerebral perfusion (partial pressure of carbon dioxide [PaCO2] < 30 mm Hg). Prolonged alkalosis has been shown to cause neuronal injury in animals and humans, providing another reason to avoid alkalosis in these patients. [30]
Jet ventilator therapy aimed at minimizing mean airway pressure and tidal volume should be used if pulmonary interstitial emphysema or a pneumothorax is present.
For treatment of persistent pulmonary hypertension of the newborn (PPHN), inhaled nitric oxide is the pulmonary vasodilator of choice. [31] Oxygen is also a potent pulmonary vasculature vasodilator. Phosphodiesterase inhibitors, including sildenafil and milrinone, are being increasingly used as adjunctive therapies for PPHN.
Pay careful attention to systemic blood volume and blood pressure. Volume expansion, transfusion therapy, and systemic vasopressors are critical in maintaining systemic blood pressure greater than pulmonary blood pressure, thereby decreasing the right-to-left shunt through the patent ductus arteriosus. Dopamine is often the first-line vasopressor for neonates with MAS requiring vasopressor support.
Ensure adequate oxygen carrying capacity by maintaining the hemoglobin concentration at a minimum of 13 g/dL.
Corticosteroids are not recommended. Evidence supporting the use of steroids in the management of MAS is insufficient. [32]
Neonates with MAS have historically been routinely treated with empiric broad-spectrum antibiotics, but this practice is being increasingly called into question. No studies have shown prophylactic antibiotics to reduce the incidence of sepsis in neonates born through meconium-stained amniotic fluid; thus, antibiotic use may be reserved for suspected or documented infections.
ECMO is used if all other therapeutic options have been exhausted. Although it is effective in treating MAS and is associated with a very low mortality rate, [33] note that ECMO is associated with a high incidence of poor neurologic outcomes. [34]
Consultations
Evaluation by a pediatric cardiologist is necessary for echocardiographic assessment of the cardiac structures and to assess the severity of pulmonary hypertension and right-to-left shunting.
Evaluation by a pediatric neurologist is helpful in the presence of neonatal encephalopathy or seizure activity.
Transfer
Although initial stabilization is necessary at community hospitals, infants with MAS frequently require high-frequency ventilation, inhaled nitric oxide (NO), or ECMO. Therefore, infants with a significant aspiration should be transferred to a regional NICU as soon as possible.
Diet
Perinatal distress and severe respiratory distress preclude feeding at the early stages of the disease.
Intravenous fluid therapy begins with adequate dextrose infusion to prevent hypoglycemia. Intravenous fluids should be provided at mildly restricted rates (60-70 mL/kg/day).
Progressively add electrolytes, protein, lipids, and vitamins to ensure adequate nutrition and to prevent deficiencies of essential amino acids and essential fatty acids.
Outpatient care
Infants with MAS are at increased risk for adverse developmental outcomes and should be referred for developmental assessment as an outpatient.
Surgical Care
Although primary management of air leak syndromes (pneumothorax or pneumopericardium) is achieved by thoracic drainage tubes inserted by a neonatologist, a pediatric surgical consultation may be necessary in severe cases. Therapy with fibrin glue has been shown to be effective in patients with a persistent air leak. [35]
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Air trapping and hyperexpansion from airway obstruction.
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Acute atelectasis.
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Pneumomediastinum from gas trapping and air leak.
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Left pneumothorax with depressed diaphragm and minimal mediastinal shift because of noncompliant lungs.
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Diffuse chemical pneumonitis from constituents of meconium.
