Meconium aspiration in labor

Meconium aspiration during labor may cause chemical pneumonitis and mechanical bronchial obstruction, resulting in respiratory failure. Examination reveals tachypnea, wheezing, cyanosis, or desaturation.

The diagnosis is suspected if the baby develops respiratory distress after birth in the presence of meconium-stained amniotic fluid, and the diagnosis is confirmed by chest radiography. Treatment of intrapartum meconium aspiration involves suctioning the contents of the mouth and nose immediately after birth before the baby takes his first breath, followed by respiratory support if necessary. Prognosis depends on the underlying physiological stress mechanisms.

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Causes of meconium aspiration during labor

Physiologic stress during labor and delivery (due to hypoxia caused by umbilical cord compression or placental insufficiency or infection) may cause meconium to pass into the amniotic fluid before birth; meconium passage occurs in approximately 10–15% of births. During delivery, approximately 5% of infants who pass meconium aspirate the meconium, causing lung injury and respiratory failure, called meconium aspiration syndrome.

Postterm infants born with oligohydramnios are at risk for more severe forms of the disease because the less dilute meconium is more likely to cause airway obstruction.

Predisposing factors:

• preeclampsia, eclampsia;
• arterial hypertension;
• post-term pregnancy;
• diabetes mellitus in the mother;
• decreased fetal motor activity;
• intrauterine growth retardation;
• mother's smoking;
• chronic lung diseases, cardiovascular system.

The mechanisms by which aspiration induces the clinical syndrome probably involve cytokine release, airway obstruction, surfactant inactivation, and/or chemical pneumonitis; underlying physiologic stressors may also be involved. If complete bronchial obstruction occurs, atelectasis results; partial obstruction leads to air trapping, where air enters
the alveoli on inspiration but cannot escape on expiration, leading to lung overinflation and possible pneumothorax with pneumomediastinum. Continued hypoxia may lead to persistent pulmonary hypertension of the newborn.

Also during labor, infants may aspirate vernix caseosa, amniotic fluid, or maternal or fetal blood, which may result in respiratory distress and signs of aspiration pneumonia on chest X-ray.

Treatment is supportive; if bacterial infection is suspected, cultures should be taken and antibacterial therapy initiated.

Pathogenesis

Hypoxia and other forms of intrauterine stress of the fetus provoke increased intestinal peristalsis, relaxation of the external anal sphincter and passage of meconium. With increasing gestational age, this effect increases. That is why, when staining the OPV with meconium in the case of the birth of a premature baby, it should be considered that he suffered more severe hypoxia than a post-term newborn.

The occurrence of convulsive inhalations in the fetus during hypoxia in the ante- or intranatal periods can lead to aspiration of meconium fluid. Penetration of meconium into the distal parts of the respiratory tract causes their complete or partial obstruction. In areas of the lungs with complete obstruction, atelectasis is formed, with partial obstruction, the formation of "air traps" and overstretching of the lungs (valve mechanism) occurs, which increases the risk of air leakage to 10-20%.

Two factors play a role in the development of aspiration pneumonia: bacterial - due to the low bactericidal effect of mechanical OPV - and chemical - due to mechanical action on the mucous membrane of the bronchial tree (pneumonitis). Edema of the bronchioles occurs, the lumen of the small bronchi narrows. Uneven ventilation of the lungs due to the formation of areas with partial obstruction of the airways and the accompanying pneumonia cause severe hypercapnia and hypoxemia. Hypoxia, acidosis and pulmonary distension cause an increase in vascular resistance in the lungs. This leads to right-left shunting of blood at the level of the atria and arterial duct and further deterioration of blood oxygen saturation.

Symptoms of meconium aspiration during labor

Symptoms of meconium aspiration may vary, depending on the severity of hypoxia, the amount and viscosity of the aspirated amniotic fluid. As a rule, children are born with a low score on the Apgar scale. In the first minutes and hours of life, depression of the central nervous system functions associated with perinatal hypoxia is noted.

Aspiration of large amounts of amniotic fluid in a newborn causes acute airway obstruction, which manifests itself as deep, gasping breaths, cyanosis, and impaired gas exchange.

When amniotic fluid is aspirated into the distal airways without complete obstruction, meconium aspiration syndrome develops due to increased airway resistance and the formation of "air traps" in the lungs. The main symptoms of this condition are tachypnea, nasal flaring, intercostal retractions, and cyanosis. In some children without acute airway obstruction, clinical manifestations of meconium aspiration may appear later. In such cases, mild meconium aspiration syndrome is observed immediately after birth, the manifestations of which increase over several hours as the inflammatory process develops. When "air traps" form in the lungs, the anteroposterior size of the chest increases significantly. Auscultation reveals moist rales of various sizes and stridor breathing.

With a favorable course, even in the case of massive aspiration, the X-ray is normalized by the 2nd week, but increased pneumatization of the lungs, areas of fibrosis, pneumatocele can persist for several months. Mortality in case of meconium aspiration in case of untimely sanitation of the tracheobronchial tree reaches 10% due to complications (air leaks, infections).

Signs of meconium aspiration include tachypnea, nasal flaring, chest wall retractions, cyanosis and decreased oxygen saturation, rales, and greenish-yellow staining of the cord, nail beds, and skin. Meconium staining may also be seen in the oropharynx and (if intubated) in the larynx and trachea. Newborns with air trapping may have a barrel chest and symptoms and signs of pneumothorax, interstitial pulmonary emphysema, and pneumomediastinum.

Diagnosis of meconium aspiration during labor

The diagnosis is suspected if the neonate shows signs of respiratory distress at delivery with meconium-stained amniotic fluid, and is confirmed by chest radiography showing hyperventilation with areas of atelectasis and flattening of the diaphragm. Fluid may be seen in the interlobular areas and pleural space, and air may be found in the soft tissues and mediastinum. Because meconium can promote bacterial growth, and meconium aspiration syndrome is difficult to differentiate from bacterial pneumonia, blood cultures and tracheal aspirate should also be obtained.

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Treatment of meconium aspiration during labor

Immediate treatment, indicated in all infants with meconium-stained amniotic fluid, includes vigorous suctioning of the mouth and nasopharynx using a De Li device immediately after the baby's head emerges and before the baby takes its first breath and cries. If suctioning does not reveal meconium in the fluid and the baby appears alert, observation without further intervention is indicated. If the baby has difficulty breathing or respiratory depression, decreased muscle tone, or bradycardia (less than 100 bpm), endotracheal intubation with a 3.5- or 4.0-mm tube should be performed. A meconium aspirator connected to an electric suction pump is attached directly to the endotracheal tube, which then serves as a suction catheter. Suctioning is continued until the endotracheal tube is removed. Re-intubation and endotracheal prolapse are indicated if respiratory failure persists, followed by mechanical ventilation and intensive care if necessary. Because endotracheal prolapse increases the risk of pneumothorax, regular follow-up (including physical examination and chest radiography) is important to detect these complications; they should be a primary consideration in children with endotracheal prolapse whose blood pressure, microcirculation, or oxygen saturation suddenly deteriorate.

Additional treatment for meconium aspiration during labor may include surfactant for infants on mechanical ventilation with high oxygen demand, which may reduce the need for extracorporeal membrane oxygenation. Antibacterial therapy is indicated for meconium aspiration, as it promotes bacterial growth. They start with cephalosporins and aminoglycosides. Often, children with meconium aspiration in the first day of life have pulmonary hypertension, hypovolemia, pathological acidosis, hypoglycemia, hypocalcemia, etc. It is necessary to monitor the level of glycemia, acid-base balance (ABB), ECG, blood pressure, and basic electrolytes with their subsequent correction. As a rule, children are not fed in the first day; from the 2nd day of life, it is advisable to start enteral feeding using a nipple or tube, depending on the severity of the condition. If enteral feeding is impossible, infusion therapy is carried out.

Treatment of air leak syndrome, a complication of air trapping, is discussed below.

Prevention

Prevention begins with identifying the above predisposing factors and correcting them. During labor, if there is a high risk of fetal hypoxia, the fetus's condition is monitored. If the assessment results indicate a critical condition of the fetus, delivery by the most appropriate method is indicated (cesarean section, obstetric forceps).

Outpatient observation

Outpatient observation of children who have undergone meconium aspiration is carried out by a local pediatrician (once a month), a neurologist and an ophthalmologist (once every 3 months).

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What is the prognosis for meconium aspiration during labor?

Meconium aspiration during labor generally has a favorable prognosis, although there is variation depending on the underlying physiological stressors; overall mortality is somewhat increased. Infants with meconium aspiration syndrome may be at increased risk of developing asthma later in life.