Meconium aspiration syndrome

Introduction to meconium aspiration syndrome Meconium aspiration syndrome (MAS), also known as meconium aspiration pneumonia (mainly meconium aspiration pneumonia), mainly in the fetus or in the process of inhalation of meconium-stained amniotic fluid, airway obstruction, intrapulmonary inflammation and A series of systemic symptoms, severe cases of respiratory failure or death, more common in term infants and expired children, the history of pregnancy often have fetal distress, extended labor, placental insufficiency, dystocia and so on. basic knowledge Sickness ratio: 0.25% Susceptible population: fetus Mode of infection: non-infectious Complications: atelectasis emphysema, mediastinal emphysema, pneumothorax, pneumonia, pulmonary hypertension

Causes of meconium aspiration syndrome

(1) Causes of the disease

Intrauterine distress

A large amount of amniotic fluid meconium inhalation can initiate and delivery during the period of labor inactivity. It is generally considered that MAS is associated with intrauterine distress, when the fetus undergoes asphyxia and acute or chronic hypoxemia during intrauterine or childbirth. Blood flow redistribution, intestinal and skin blood flow decreased, resulting in intestinal wall ischemia, anal sphincter relaxation and meconium discharge, the incidence of meconium-contaminated amniotic fluid in live births is about 12% to 21.9%, hypoxia to the fetus The stimulation of the respiratory center causes the respiratory movement to generate a strong wheezing from irregular and gradually, and the meconium is inhaled into the nasopharynx and the trachea. The effective breathing after the delivery of the fetus causes the meconium in the upper respiratory tract to be inhaled into the lungs. Due to increased intestinal system maturity and intestinal peptide levels and placental dysfunction, the likelihood of developing MAS is greater than that of term infants.

2. Fetal maturity

At present, the data does not fully support the correlation between MAS and intrauterine distress. The changes in fetal heart rate, Apgar score, fetal scalp blood pH and other indicators are not related to amniotic fluid meconium contamination, but the risk of MAS increases with gestational age. Look, suggesting that intrauterine meconium discharge is related to fetal parasympathetic development and reflex regulation after umbilical cord compression, and meconium discharge also reflects the natural phenomenon of fetal digestive tract development, when the fetus is stimulated ( Extrusion, umbilical cord knot, asphyxia, acidosis, etc.), the fetal anal sphincter relaxes and excretes meconium into the amniotic fluid, while the reflex begins deep breathing, inhaling contaminated amniotic fluid and meconium into the airway and lungs.

3. Fetal distress in the labor process

Under normal circumstances, the lung endocrine fluid keeps the lung fluid flowing to the amniotic sac. The actual amplitude of intrauterine respiratory movement is very small. Even if a small amount of meconium enters the amniotic fluid and is not inhaled into the lungs, it will decrease with amniotic fluid in the late pregnancy. Factors such as the initiation of stimulation of the fetus, which may be manifested as signs of distress in the fetus, are inhaled into the lungs.

(two) pathogenesis

1. Airway obstruction and inflammation in the lungs

Viscous meconium particles entering the airway can completely block the bronchus, causing mechanical obstruction, leading to atelectasis of the lungs or segments of the lungs, alveolar ventilation - imbalance of blood perfusion; valvular obstruction in the small airways is more likely to cause pneumothorax, interstitial Emphysema or mediastinal emphysema, aggravation of ventilatory disorders, acute respiratory failure, meconium bile acid, bile salts, biliverdin, trypsin, enteric acid, etc., and subsequent secondary infection can cause lung Histochemical, infectious inflammatory response, hypoxemia and acidosis, when the airway is partially blocked, because of high airway pressure, it is easier for gas to enter the peripheral alveoli, and the pressure of the exhaust gas is low, causing partial blockage of the airway. It becomes completely obstructed, and the peripheral alveolar gas retention leads to emphysema. When the lung tissue is over-expanded, it shows signs of intercostal fullness and lower pressure. The meconium in the large airway can stimulate the mucous membrane, produce inflammation and chemical pneumonia. .

2. Ventilation and ventilation dysfunction

If the meconium in the airway is not absorbed and removed in time after resuscitation, it will gradually move into the small airway and peripheral lung tissue. The meconium entering the alveoli can inhibit the pulmonary surfactant, causing local alveolar collapse and the lungs Under the combined influence of the above reasons, there are obstacles in ventilation and ventilation function, such as persistent hypoxemia, hypercapnia and acidosis. In severe cases, pulmonary hypertension occurs, and meconium particles entering the alveoli can be immediately taken up by alveolar macrophages. Cells are engulfed and digested.

3. Transparent film formation

Because MAS is often associated with prenatal, postpartum and postpartum hypoxia, it may have a greater impact on the pathological damage of the lungs in the early postnatal period. Airway and alveolar epithelial cells may be degenerated, necrotic, and shed due to hypoxia. There is a large amount of exudation and formation of a transparent film in the alveoli.

4. Pulmonary hypertension and acute lung injury, intrauterine hypoxemia can cause pulmonary vascular muscle hypertrophy

It is the cause of increased pulmonary vascular resistance - perinatal asphyxia, acidosis, hypercapnia and hypoxemia cause pulmonary vasoconstriction, persistent pulmonary hypertension (PPH), atrial or catheter The horizontal right-to-left shunt further aggravates the condition. In recent years, studies have shown that MAS can cause pulmonary vascular endothelial damage, and can damage alveolar type II cells, reduce pulmonary surfactant, and cause alveolar collapse and lung clear film formation. Injury manifests, forms pulmonary edema, pulmonary hemorrhage, and aggravates hypoxia.

Meconium aspiration syndrome prevention

The key point is to actively prevent fetal asphyxia and hypoxia; when meconium is contaminated with amniotic fluid, it emphasizes the removal of the respiratory tract before and after the delivery of the shoulder, and the meconium of the mouth, nose and throat; if the meconium is thick, the baby does not cry, and strives to establish in the breath. Intubation and attraction immediately before the trachea; injection of nikethamide, lobeline and other respiratory stimulants are strictly prohibited. (The above information is for reference only, please consult your doctor for details.)

Meconium aspiration syndrome complications Complications atelectasis emphysema mediastinal emphysema pneumothorax pneumonia pulmonary hypertension

With the degree of obstruction, complicated with atelectasis, emphysema, mediastinal emphysema and pneumothorax, severe hypoxic acidosis can cause intracranial hemorrhage and pulmonary hemorrhage. Patients with prolonged disease often have interstitial pneumonia and pulmonary fibrosis.

1. Air leak and pneumothorax

As the meconium occludes the small airway, the air sag causes the alveolar to rupture and become a bullae. If the pleural visceral ruptures, pneumothorax may occur. If the gas leaks along the small interstitial vascular sheath, it may cause mediastinal emphysema and pericardial effusion. In the treatment, pneumothorax can be treated by closed thoracic drainage, and muscle relaxant can be used to suppress excessive spontaneous breathing activity.

2. Continuous pulmonary hypertension

Generally treated with inhaled nitric oxide, see continuous pulmonary hypertension.

3. Intracranial hemorrhage and pulmonary bleeding

Severe oxyacidosis can cause intracranial hemorrhage and pulmonary hemorrhage.

4. Pulmonary complications

Patients with prolonged disease often have interstitial pneumonia and pulmonary fibrosis.

Meconium aspiration syndrome symptoms common symptoms meconium contamination cyanosis hypercapnia hypoxemia erythrocytosis hypocalcemia alar fluttering atelectasis

The severity of the disease varies greatly depending on the severity of the hypoxic damage and the amount and viscosity of the meconium-stained amniotic fluid. The less inhaled can be asymptomatic at birth; a large amount of inhaled meconium can cause stillbirth or postnatal Soon died.

1. Meconium contamination: Meconium-contaminated amniotic fluid, if the child is exposed to meconium-contaminated amniotic fluid in the uterus for >4-6 hours, the whole body skin, the nail and the umbilical cord are dyed yellow-green or dark green at birth.

2. Respiratory distress: Most children often have shortness of breath (breathing frequency > 60 times / min), breathing difficulties, cyanosis, nose flapping, sputum, and three concave signs. The severity of amniotic fluid contaminated by meconium is not First, the degree of respiratory distress can also vary, the general cases often appear within 4 hours after birth, mild cases only show temporary dyspnea, often self-healing, heavier dyspnea and bruising, but need to inhale 40% oxygen can maintain normal PaO2 and PaCO2. In severe cases, it can die within a few minutes after birth or severe dyspnea and bruising within a few hours after birth. Generally, oxygen therapy is ineffective and requires comprehensive treatment such as mechanical ventilation. Some children At first, only mild respiratory distress can be expressed, but after a few hours, the condition may worsen due to chemical pneumonia.

3. Airway obstruction to the barrel chest: thick meconium-contaminated amniotic fluid can cause obstruction or semi-blocking of the airway after inhalation of the airway. The two lungs often have a voice, a thick wet voice, and appear later. The clinical manifestations of acute airway obstruction are asthmatic breathing, cyanosis, and must be immediately absorbed into the trachea. Children with airway obstruction have a barrel-shaped chest due to gas retention. Shortness of breath, decreased breathing sound or wet snoring and wheezing. If the clinical symptoms suddenly deteriorate, the pneumothorax should be suspected, and the incidence rate is 20% to 50%. When the pneumothorax occurs, the cyanosis and dyspnea may suddenly increase.

4. Continuous pulmonary hypertension: some children may have persistent pulmonary hypertension (see continuous pulmonary hypertension), due to a large number of right to left shunt, in addition to causing severe blue ultraviolet, heart enlargement, liver enlargement and other heart failure.

5. Others: severe meconium aspiration and acute hypoxia children often have disturbance of consciousness, increased intracranial pressure, convulsions and other central nervous system symptoms and polycythemia, hypoglycemia, hypocalcemia and pulmonary hemorrhage.

Examination of meconium aspiration syndrome

1. Blood: Infectious blood.

2. Blood gas examination: pH drop, PaO2 decreased, PaCO2 increased, manifested as hypoxemia and hypercapnia, may have severe mixed acidosis, if the radial artery or right iliac artery PaO2 is higher than femoral artery PaO2 : 1.9 kPa (15 mmHg) or more, indicating that there is a right-to-left shunt at the arterial catheter.

Chest X-ray film is of great significance for the diagnosis of MAS. The inhaled meconium usually reaches the alveoli after 4 hours after birth, and the chest X-ray can show special performance. The X-ray signs of about 85% of MAS children are most obvious at 48h after birth, but About 70% of MAS children with chest X-ray findings can not be consistent with clinical manifestations, according to chest X-ray findings MAS into:

3. Mild: thickened lung texture, mild emphysema, mild decrease of diaphragm, normal heart shadow, indicating inhalation of thin meconium.

4. Moderate: The lung field has coarse particles or flaky agglomerates with increased density, cloud-like shadows or segmental atelectasis, with mild translucent cystic emphysema, and small heart shadow.

5. Severe: In addition to the above moderate performance, accompanied by interstitial emphysema, mediastinal gas or pneumothorax and other air leakage.

Diagnosis and differential diagnosis of meconium aspiration syndrome

diagnosis

The main points of clinical diagnosis of MAS are as follows:

1. History of intrauterine distress: If there is intrauterine distress or suffocation, the Apgar score can be performed at 1, 5, and 10 minutes after birth, less than 3 points, which may be severe asphyxia, but the severe MAS Apgar score may be 3~ 6 points, which is not proportional to the degree of clinical respiratory distress.

2. Meconium-contaminated amniotic fluid during childbirth: This is an important clinical diagnosis for respiratory distress. If a large amount of meconium is contaminated in the baby's skin, nails, umbilical cord, or meconium from the mouth and airway during childbirth, then The cause of respiratory distress can be basically determined.

3. Clinical symptoms of dyspnea: generally manifested as progressive dyspnea, intercostal depression, 12 to 24 hours after birth, with fetal meconation into the peripheral lungs, showing increased difficulty in breathing, airway attracting meconium contamination Liquid, dyspnea may be caused by airway obstruction, which makes it difficult to expand the alveoli. However, due to asphyxia, the fetal lung fluid can not be discharged and hypoxic pulmonary vasospasm. Physical examination can find that the thorax is full, etc., due to emphysema. .

4. Radiological examination: signs of meconium granules, atelectasis and emphysema.

5. Blood gas examination: severe MAS blood gas examination showed hypoxemia and hypercapnia, may have severe mixed acidosis, must rely on airway intubation and mechanical ventilation.

Differential diagnosis

1. Neonatal respiratory distress syndrome: multiple premature infants, progressive pulmonary atelectasis due to insufficient pulmonary surfactant, rapid onset, progressive dyspnea, cyanosis, inspiratory tri-concavity, expiratory sputum, X The chest radiographs showed a general decrease in the brightness of both lungs and bronchial aeration.

2. Amniocentesis aspiration pneumonia: simple amniotic fluid inhalation is easier to absorb, with mild symptoms and less complications.

The material in this site is intended to be of general informational use and is not intended to constitute medical advice, probable diagnosis, or recommended treatments.