Amniotic fluid and meconium aspiration syndrome

　　The main causes of amniotic fluid and meconium aspiration syndrome include intrauterine distress, fetal maturity, and fetal distress during labor. The specific details are as follows:

　　1. Intrauterine Distress

　　A large amount of amniotic fluid meconium aspiration can occur before the onset of labor, during the stage of labor and delivery. It is generally believed that MAS is related to fetal intrauterine distress, when the fetus experiences asphyxia and acute or chronic hypoxemia during intrauterine or labor processes, the redistribution of blood flow in the body, a decrease in blood flow to the intestines and skin, leading to ischemic spasm of the intestinal wall, relaxation of the anal sphincter, and the excretion of meconium. The stimulation of hypoxia to the fetal respiratory center causes respiratory movements to become irregular and gradually develop into strong coughing, aspirating meconium into the nasopharynx and trachea; while the effective respiration after the fetus is delivered further causes the aspiration of meconium into the lungs from the upper respiratory tract. The possibility of MAS in post-term infants is increased compared to full-term infants due to the higher level of intestinal nervous system maturity and intestinal peptides, as well as poor placental function.

　　2. The maturity of the fetus

　　The current data does not fully support the correlation between MAS and fetal distress in utero, as there is no correlation between fetal heart rate changes, Apgar scores, fetal scalp blood pH values, and amniotic fluid meconium contamination. However, according to the increasing risk of MAS with gestational age, it suggests that the excretion of meconium in utero is related to the maturation of fetal parasympathetic nervous system development and the reflexive regulation after umbilical cord compression, and the excretion of meconium also reflects the natural phenomenon brought by the maturation of the fetal digestive tract. When the fetus is stimulated (squeezed, umbilical cord knot, asphyxia, acidosis, etc.), the fetal anal sphincter relaxes and meconium is excreted into the amniotic fluid, while reflexive deep breathing begins, inhaling contaminated amniotic fluid and meconium into the airway and lungs.

　　3. Fetal distress during labor

　　Under normal circumstances, the secretions in the lung keep the fluid in the amniotic sac flowing, and the actual amplitude of fetal breathing movements in utero is very small. Even if a small amount of meconium enters the amniotic fluid, it will not be inhaled in large quantities into the lungs. However, with the reduction of amniotic fluid in the later stages of pregnancy, the onset of labor, and other factors such as the stimulation of fetal movements, it may be manifested as signs of fetal distress and inhaled into the lungs.

　　Simple amniotic fluid aspiration is easier to absorb, and secondary pneumonia is less common. Children with meconium-amniotic fluid aspiration may develop atelectasis, emphysema, mediastinal emphysema, and pneumothorax depending on the degree of obstruction. Severe hypoxia and acidosis can lead to intracranial hemorrhage and pulmonary hemorrhage. Chronic cases often have interstitial pneumonia and pulmonary fibrosis. When complications such as pneumothorax or mediastinal emphysema occur, sudden breathing difficulties and worsening cyanosis may occur, with severe cyanosis in severe cases, indicating concurrent neonatal persistent pulmonary hypertension.

　　The severity of the condition in children with amniotic fluid and meconium aspiration syndrome varies greatly, differing according to the severity of hypoxia damage, the amount and viscosity of meconium-contaminated amniotic fluid inhaled. Those inhaling less may have no symptoms at birth, while large amounts of inhaled meconium can lead to stillbirth or death shortly after birth. If the child is exposed to meconium-contaminated amniotic fluid in utero for more than 4 to 6 hours, the entire skin, nails, and umbilical cord may be stained yellow-green or dark green at birth.

　　Respiratory distress is mainly manifested as shortness of breath (>60 times per minute), nasal flaring, three凹陷 signs, and cyanosis. Due to the varying severity of meconium contamination of amniotic fluid, the degree of respiratory distress can also vary. Generally, mild cases often appear within 4 hours after birth, with only transient difficulty in breathing, which often heals spontaneously. Severe cases may have difficulty breathing and cyanosis, but require inhalation of 40% oxygen to maintain normal PaO2 and PaCO2. Severe cases may die within minutes after birth or may develop severe respiratory distress and cyanosis within a few hours after birth. Generally, oxygen therapy is ineffective, and comprehensive treatment such as mechanical ventilation is required. Some children may initially only show mild respiratory distress, but may deteriorate due to chemical pneumonia a few hours later.

　　After inhaling thick, meconium-contaminated amniotic fluid, the child may suffer from airway obstruction or partial obstruction. The clinical manifestations of acute airway obstruction include wheezing respiration and cyanosis, and immediate endotracheal aspiration is required. Children with partial airway obstruction may present with increased anteroposterior chest diameter, barrel-shaped chest, shallow breathing, decreased breath sounds, or moist rales and wheezing. When pneumothorax occurs, cyanosis and increased difficulty breathing may suddenly appear, and some children may develop persistent pulmonary hypertension.

　　The prevention of amniotic fluid and meconium aspiration syndrome mainly involves avoiding prolonged labor, incomplete placental function, difficult labor, and other factors. Properly handle fetal distress before and during labor to minimize aspiration. It is extremely important to clear the oropharyngeal and nasal mucus before the first breath, or to use a disposable syringe to clear it, which is crucial for reducing the incidence. The key is to actively prevent and treat fetal asphyxia and oxygen deficiency, and strictly prohibit the injection of respiratory stimulants such as nikethamide and lobeline. Amniotic fluid contaminated with meconium often indicates fetal oxygen deficiency, but full-term or post-term infants may have a physiological small amount of meconium excreted into the amniotic fluid.

　　The main examinations for amniotic fluid and meconium aspiration syndrome include arterial blood gas analysis and chest X-ray, as follows:

　　1. Arterial blood gas analysis

　　Hypoxemia is a characteristic manifestation. Mild children may develop respiratory alkalosis due to excessive breathing. Severe children often present with increased PaCO2 and respiratory acidosis due to airway obstruction. If the child is asphyxiated, blood gas analysis may show mixed acidosis.

　　2. Chest X-ray

　　The inhaled meconium usually reaches the alveoli 4 hours after birth, at which time the chest X-ray can show special manifestations. About 85% of the X-ray signs of infants with amniotic fluid and meconium aspiration syndrome are most pronounced within 48 hours after birth, but about 70% of the chest X-ray manifestations of infants with amniotic fluid and meconium aspiration syndrome may not be consistent with clinical manifestations. The amniotic fluid and meconium aspiration syndrome is divided into mild, moderate, and severe according to chest X-ray findings. In the mild stage, the lung vessels are thickened, there is mild emphysema, the diaphragm is slightly dropped, and the heart shadow is normal; in the moderate stage, there are dense coarse particles or patchy masses and cloud-like shadows in the lung fields, or segmental atelectasis, accompanied by low-grade lucid cystic emphysema, and the heart shadow is smaller. In the severe stage, in addition to the moderate manifestations mentioned above, there are interstitial emphysema, mediastinal gas accumulation, or pneumothorax, and other air leak phenomena.

　　Feeding and caring for newborns is also very important, with breastfeeding as the main method, and attention should be paid to the child's basic condition. In addition to general treatment methods, pregnant women can also use the following dietary methods to improve symptoms in infants with amniotic fluid and meconium aspiration syndrome through breastfeeding:

　　One: Pumpkin and Job's tears porridge

　　1. Wash the materials, mince the scallions, slice the pumpkin, blanch and remove. Cook Job's tears in boiling water for 30 minutes and remove. Separate the egg whites.

　　2. Bring the bone broth to a boil, add the pumpkin slices and cook until well-flavored, then remove and reserve the broth. Add rice and Job's tears and cook until well-blended.

　　3. Season with salt, pour in the egg white and mix well, then pour into a bowl and arrange the pumpkin slices on top. Finally, remove the goji berries and scallions.

　　Second, lotus root and oatmeal congee

　　1. Wash the materials. Cut the lotus root into slices, shred the carrots, and cut the pork rib meat into strips.

　　2. Put the rice in a pot, add water and bring to a boil, then add oatmeal and lotus root slices, bring to a boil over high heat, then reduce to low heat and cook until thickened.

　　3. Add shredded carrots and pork rib meat, cook until done, then add salt to taste.

　　For amniotic fluid with meconium contamination, after clearing the oropharynx and nasal meconium mucus, it is necessary to use a neonatal laryngoscope for examination and to insert a tracheal tube to suction it clean, and it is not suitable for positive pressure ventilation before it is completely suctioned. The contents of the stomach should also be suctioned clean to avoid vomiting and re-inhalation and other symptoms of meconium gastritis.

　　After entering the neonatal ward, it is still necessary to focus on monitoring, and ultrasonic atomization should be given every 4-6 hours to dilute, and then postural drainage, percussion, vibration, and other chest physical therapy should be performed according to the bronchial course of the lung segment occupied by the lesion, which is beneficial for疏导 obstructive objects and improve atelectasis. According to need, antibiotics, bronchodilators, and mucolytic agents can be added to the atomizing fluid. In severe cases, when blood gas is abnormal and PaCO2 is progressively elevated, sterile normal saline of 1-2ml can be injected into the trachea through the tracheal tube, and ventilation for 1-2 minutes before suctioning. This repeated lavage and suctioning should be continued until the secretions are clear. After lavage, if spontaneous breathing is strong, the tracheal tube can be removed and closely observed. If the child has spontaneous breathing and inhales high-concentration oxygen, PaO2 can be maintained at 5.33-6.67kPa (40-50mmHg), and mechanical ventilation can be omitted, and tolazoline, a vasodilator, can be given.

　　Mechanical ventilation can cause meconium particles to enter the deep lungs, so it needs to be used with caution. The principle of index adjustment is to use a higher oxygen concentration, a faster frequency, a shorter inspiratory time, a longer expiratory time, and as low a pressure as possible to reduce the occurrence of air leaks in over-inflated lungs. If there is restlessness, sedatives and muscle relaxants can be used. During oxygenation, transcutaneous oxygen monitoring should be applied to accurately guide the adjustment of oxygen concentration. Pay attention to keeping warm, maintaining a neutral temperature, closely monitoring heart rate, breathing, and blood pressure, and regularly measuring blood gas and recording intake and output. Routine administration of broad-spectrum antibiotics is recommended to prevent infection. If there is hypoglycemia, low blood calcium, pneumothorax, and other conditions, symptomatic treatment should be given.