Amniotic fluid aspiration

　　12. 1. Fetal hypoxia can cause a mass reflex to expel meconium and true respiration, inhaling corneal cells of amniotic fluid meconium together. The aspiration of thick meconium in large quantities can lead to complete tracheal obstruction and atelectasis. Acute asphyxia and hypoxia with thin amniotic fluid meconium or less aspiration can lead to partial obstruction, causing subsegmental atelectasis and obstructive emphysema. If alveolar rupture occurs, interstitial emphysema or pneumothorax may result. When gas spreads along the vascular wall and lymphatic vessels to the mediastinum, mediastinal emphysema may occur.

　　11. 2. Stimulation of the respiratory tract mucosa by amniotic fluid meconium or secondary infection may lead to pneumonia; after entering the recovery period, aspirated material may be absorbed or engulfed, and in severe cases, fibrosis may occur, leading to emphysema and other lesions.

　　10. 3. Full-body contamination with meconium at birth: if the fetus is immersed in meconium-contaminated amniotic fluid for 4 to 6 hours, the nails may become yellow-green; for 10 to 12 hours, the umbilical cord, fetal fat, placenta, and amnion may all become stained with meconium. Newborns may experience severe respiratory depression, bradycardia, low muscle tone, and shock. After the appearance of spontaneous respiration, rapid breathing, difficulty breathing, intercostal depression, and expiratory groaning may be observed. Cyanosis, such as cyanosis, may be severe, and oxygen therapy may not improve. Newborns with persistent pulmonary hypertension should be considered if there is no improvement after severe oxygen therapy. Pulmonary signs are related to the amount and thickness of aspirated meconium, and if there is pneumothorax, the respiratory sounds on both sides may be asymmetrical.

　　9. In severe asphyxia and hypoxia, cardiovascular adaptation disorders with right-to-left shunting may occur; in cases with megacardia and poor peripheral circulation, seizures may occasionally occur. Blood gas analysis shows decreased PO2, increased Pco2, and decreased pH. Severe cases may die within minutes to hours after birth; survivors may have a prolonged course, with significant improvement in general cases within 2 days; complete recovery may take 10 days or longer. In mild cases, respiratory distress may appear several hours after birth. X-ray examination may show slightly thickened pulmonary markings, mild emphysema, and a slight descent of the diaphragm. In cases with more meconium aspiration, both lungs may have dense patchy or nodular infiltrates, with excessive lung expansion and occasionally small amounts of pleural effusion, interstitial emphysema, mediastinal gas, or pneumothorax.

　　1. Complications such as pneumonia may occur, developing into amniotic fluid aspiration pneumonia.

　　2. Most of these infants have signs of intrauterine hypoxia, such as increased or decreased fetal heart rate, increased or decreased fetal movements, and require oxygen and artificial respiration at birth for rescue. After rescue, the child quickly exhibits rapid breathing, shortness of breath, cyanosis of the face or skin, and a large amount of secretions or foam in the mouth or nasopharynx.

　　4. Pulmonary examination may reveal moist rales. In cases with less amniotic fluid aspiration, symptoms are mild and can improve within 3 to 4 days. The more amniotic fluid aspirated, the more severe the symptoms, which may even lead to respiratory failure. Due to the varying amounts of aspirated amniotic fluid, the chest X-ray findings also differ, with mild cases showing increased pulmonary markings and severe cases showing patchy shadows in both lungs, more prominent in the inner and lower parts of the lungs.

　　1. The clinical manifestations of MAS infants vary according to the severity of hypoxia damage, the amount and viscosity of amniotic fluid contaminated with meconium, and the duration of exposure to the contaminated amniotic fluid in utero. If the infant is exposed to contaminated amniotic fluid for more than 4 to 6 hours in utero, the skin, nails, and umbilical cord at birth may be stained yellow-green or dark green.

　　2, Respiratory distress is mainly manifested as tachypnea (>60 times/min), nasal flaring, triad signs, and cyanosis. Due to the varying severity of meconium contamination of amniotic fluid, the degree of respiratory distress may also vary. In general, the symptoms appear within 4 hours after birth. Mild cases may only present transient dyspnea, which can often recover spontaneously. Severe cases may have dyspnea and cyanosis, but may require the administration of 40% oxygen to maintain normal PaO2 and PaCO2. Severe cases may die within a few minutes or within a few hours after birth due to severe dyspnea and cyanosis, and may require mechanical ventilation and other comprehensive treatments. Some children may initially present with mild respiratory distress, but may deteriorate due to chemical pneumonia a few hours later.

　　3, Barrel chest: Children who aspirate thick amniotic fluid contaminated with meconium may suffer from airway obstruction or partial obstruction. The clinical manifestations of acute airway obstruction include wheezing breathing, cyanosis, and it is necessary to perform endotracheal suction immediately. Children with partial airway obstruction may present with an increased anteroposterior diameter of the chest, resembling a barrel chest, shallow breathing, decreased respiratory sounds, or moist rales and wheezing. When pneumothorax occurs, sudden cyanosis and increased difficulty breathing may occur.

　　4, Some children may develop persistent pulmonary hypertension (see persistent pulmonary hypertension).

　　1, Prevention:The key is to prevent fetal hypoxia in utero or during labor. It is very necessary for mothers to have regular prenatal examinations. When signs of fetal asphyxia are found, delivery should be terminated as soon as possible. The longer the hypoxia time, the greater the possibility and amount of amniotic fluid aspiration, and prolonged intrauterine hypoxia can also cause fetal brain damage. At the moment of the child's birth, it is necessary to insert a tube to aspirate the amniotic fluid from the child's mouth, nose, oropharynx, and trachea as soon as possible to avoid aspirating these areas into the deeper lungs when the child cries, which can further worsen the condition.

　　2, Prenatal:Proper handling of fetal distress during labor is essential to avoid and reduce aspiration. It is extremely important to remove or use a disposable catheter to clear the oropharyngeal and nasal mucus before the first breath is taken, which is also the key to reducing the incidence. It is necessary for perinatal medical and nursing staff to receive qualified resuscitation training before resuming work.

　　3, Amniotic fluid:After treatment for aspiration pneumonia, the prognosis is generally good, and the vast majority of children can recover completely without any sequelae.

　　Firstly, low oxygenemia in arterial blood:

　　It is a characteristic manifestation. Mild cases may present with respiratory alkalosis due to excessive respiration. Severe cases may present with increased PaCO2 and respiratory acidosis due to airway obstruction. If the child asphyxiates, the blood gas may show mixed acidosis:

　　Secondly, fetal meconium inhalation on chest X-ray:

　　Generally, it takes about 4 hours after birth for the chest X-ray to show special manifestations. About 85% of MAS patients show the most obvious X-ray signs within 48 hours after birth, but about 70% of MAS patients may not be consistent with their clinical manifestations. According to chest X-ray findings, MAS can be divided into:

　　1, Mild degree:The pulmonary vessels are thickened, there is mild emphysema, the diaphragm is slightly descended, and the cardiac silhouette is normal.

　　2, Moderate degree:There is an increase in density of coarse granular or sheet-like mass shadow, or segmental atelectasis with clear cystic emphysema, and the cardiac silhouette is smaller than normal.

　　3. Severe:In addition to the above moderate manifestations, there are interstitial emphysema, mediastinal gas, or pneumothorax, and other air leak phenomena.

　　1. The following foods are good for the body after a large amount of amniotic fluid aspiration:

　　The milk consumed can be appropriately diluted with water; eat more light foods; in addition to milk, eggs, and soy products, fresh vegetables and fruits can also be eaten more.

　　2. It is best not to eat the following foods after a large amount of amniotic fluid aspiration:

　　High-protein diet, such as meat, chicken, fish; spicy foods; excessive sugar intake and foods that are too sweet; cold and acidic foods.

　　1. If the amniotic fluid is contaminated with meconium, after clearing the meconium mucus from the oropharynx and nose, a neonatal laryngoscope must be used for examination and tracheal intubation until it is suctioned clean. It is not advisable to use positive pressure ventilation before it is suctioned clean, and the stomach contents should also be suctioned to avoid vomiting, re-inhalation, and the occurrence of meconium gastritis.

　　2. After entering the neonatal ward, it is necessary to focus on monitoring, give ultrasonic atomization every 4-6 hours to dilute the atomization, and then, according to the bronchial course of the lung segment involved by the lesion, perform position drainage, percussion, vibration, and other chest physical therapy to facilitate the removal of obstructive objects and improve atelectasis. In the atomized solution, antibiotics, bronchodilators, and mucus solubilizers can be added as needed. In severe cases, when blood gas abnormalities occur and PaCO2 progressively increases, sterile normal saline of 1-2ml can be injected through the tracheal tube into the trachea for ventilation for 1-2 minutes, and then suction is performed again. This process is repeated until the secretions are clear. After lavage, if the spontaneous breathing is strong, the tracheal tube can be removed, and the child should be closely observed. If the child has spontaneous breathing and the intake of high-concentration oxygen can maintain PaO2 at 5.33-6.67kPa (40-50mmHg), mechanical ventilation can be omitted, and tolazoline, a vasodilator, can be administered.

　　3. Mechanical ventilation can cause meconium particles to enter the deep lung, 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 lung overinflation and air leaks. 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.

　　4. Pay attention to keeping warm, maintaining a neutral temperature, closely monitoring heart rate, breathing, and blood pressure, regularly measuring blood gas, and giving broad-spectrum antibiotics to prevent infection. In case of hypoglycemia, low blood calcium, pneumothorax, and other conditions, symptomatic treatment should be provided.