Treatment and prevention of meconium aspiration syndrome

Intrapartum amnioinfusion in the presence of meconium in the fluid

This procedure is most indicated in the presence of amniotic fluid heavily stained with meconium. The results of four randomized studies of recent years were processed by means of a meta-analysis by Hofmeyr. As a result, a decrease in the frequency of cesarean sections for fetal indications (fetal distress) was established, a significant decrease in the number of newborns in whom meconium was located in the respiratory tract not below the vocal cords was noted, and meconium aspiration syndrome was significantly less frequent. No perinatal deaths were noted in either the amnioinfusion group or the control group.

Complications of amnioinfusion include the development of uterine hypertonicity and, possibly, neonatal respiratory failure.

As is known, respiratory distress can develop immediately after birth. However, its symptoms most often appear after 12-24 hours in the form of cyanosis, tachypnea, wheezing, widening or retraction of the intercostal spaces, or overstretching of the chest. Auscultation reveals coarse wheezing, gentle crepitation, and prolonged expiration. Radiographically, areas of large, irregularly shaped darkening alternating with areas of increased transparency are visible. Often the lungs look emphysematous, the diaphragm is flattened, the bases of the lungs are highly transparent, and the anteroposterior size of the chest is increased. In 1/2 of cases, fluid and air are detected in the pleura and interlobar spaces. Pneumothorax usually develops within the first 24 hours, often spontaneously in newborns who have not received artificial ventilation. The radiographic symptom of a "snow storm" and cardiomegaly are characteristic of profuse aspiration. It should be noted that there are no radiographic symptoms pathognomonic for meconium aspiration, and it is sometimes difficult to differentiate it from pneumonia and pulmonary hemorrhage. The radiographic picture usually normalizes after 2 weeks, but increased pneumatization of the lungs and the formation of pneumatocele can be observed for several months.

Metabolic acidosis in the first hours after birth indicates that the neonate has already been asphyxia. Initially, minute ventilation is normal or even slightly increased, but in more severe cases, the development of hypercapnia requires artificial ventilation. The severity of hypoxemia largely depends on the degree of lung damage, as well as persistent pulmonary hypertension. While mild cases may be managed with oxygen therapy for several hours or days, severe cases may develop respiratory distress or require prolonged (days, weeks) artificial ventilation. Respiratory complications such as air leakage, secondary infection, and bronchopulmonary dysplasia prolong the recovery. Combined complications, including hypoxic-ischemic encephalopathy, renal failure, coagulopathy, and necrotizing enterocolitis, are caused by perinatal asphyxia, not by meconium aspiration.

Treatment of meconium aspiration syndrome in the delivery room

• suctioning the contents of the oropharynx immediately after the birth of the head until the baby takes his first breath;
• additional heating for the child;
• removal of meconium from the mouth, throat, nasal passages and stomach after the birth of the child;
• tracheal intubation followed by sanitation of the tracheobronchial tree;
• Manual ventilation with an Ambu bag through a mask or an intubation tube.

Next, the method of oxygen therapy is determined: through a mask, oxygen tent for mild aspiration; artificial ventilation for massive aspiration after removing meconium from the trachea by infusing 1-2 ml of sterile isotonic sodium chloride solution into the trachea. Sanitation in the first 2 hours of life is repeated every 30 minutes, using postural drainage and back massage.

Prevention of meconium aspiration

In order to improve the possibilities of preventing neonatal aspiration syndrome, a new method of intra-amniotic perfusion of amniotic fluid during labor with its microfiltration has been developed and studied.

It should be emphasized that in modern literature much attention is paid to determining the concentration of meconium in amniotic fluid, which is divided into recently passed meconium ("fresh"), an increase in the concentration of which requires rapid delivery, and "old". Thus, scientists have developed a method for spectrophotometric determination of meconium concentration in waters using the principle of determining bilirubin in hemolytic disease of the fetus and newborn. Meconium is determined in the spectrum of 410 nm (405-415 nm) and the amount can fluctuate in confidence intervals from 370 to 525 nm. Weitzner et al. also developed an objective method for determining the content of meconium in waters, since the amount of meconium is usually determined subjectively, visually and is divided into two types: minor admixture and significant admixture of meconium in waters. The authors have developed a simple, fast and inexpensive method for determining meconium in waters ("Meconium crit") and its concentration in waters. The method was as follows: 15 g of fresh neonatal meconium (no more than 3 hours old) was taken, placed in clear amniotic fluid and observed for 15 minutes. Then 15 g of meconium was diluted in 100 ml of amniotic fluid and then diluted in a concentration of 10 g, 7.5 g, 5 g, 3 g and 1.5 g per 100 ml of amniotic fluid. Then 1 ml of each sample was additionally diluted with clean water 0.5 ml, 1 ml, 2 ml, 4 ml and 9 ml. 10 ml of the meconium and water mixture was placed in a standard tube for determining hematocrit, centrifuged and then the amount of meconium was determined as hematocrit is determined. These methods are important, since the development of aspiration syndrome (about 2%) can lead to neonatal mortality in more than 40% of newborns. In the presence of so-called "thick" meconium, the incidence of complications in newborns increases. Therefore, a number of authors perform amnioinfusion in the presence of "thick" meconium. In contrast to the method of Molcho et al., which requires a very strong dilution of meconium below the clinically significant (1 g / 100 ml was the maximum concentration), the method of Weitzner et al. usually uses those concentrations of meconium that are observed in clinical practice and only requires the presence of a centrifuge in the delivery room. Nuclear magnetic resonance is also used to determine meconium in amniotic fluid. In two independent studies, doctors determined the presence of "thick" meconium in amniotic fluid using echography. Ohi, Kobayashi, Sugimura, Tegao developed a new method for determining meconium in amniotic fluid using monoclonal antibodies with the determination of a component of meconium - a glycoprotein of the mucin type. Horiuchi et al. also isolated and identified zinc coproporphyrin as the major fluorescent component of meconium.

The work by Davey, Becker, Davis describes new data on meconium aspiration syndrome: physiological and inflammatory changes in a model of newborn piglets. It is shown that meconium aspiration syndrome causes an acute decrease in gas exchange and dynamic plasticity of the lungs, which return to the initial level after 48 hours. Endogenous surfactant function is also significantly inhibited by meconium. All signs of lung injury were significantly more pronounced in the group of animals with meconium in the water. According to Kariniemi, Harrela, the latter is more associated with placental insufficiency compared to umbilical blood flow insufficiency. Based on these data, amnioinfusion should be performed as early as possible in labor, since it simultaneously improves the condition of the fetus and prevents fetal distress.

It should be emphasized that, according to Parsons, the meconium aspiration syndrome remains constant within 6.8-7%. Other authors determine the frequency of about 2%, despite active suction of meconium from the upper respiratory tract. At the same time, in the work of Carson et al., where mucus suction was not performed, the frequency of aspiration syndrome remained low. Therefore, Goodlin believes that a more effective method of treating meconium aspiration syndrome is to induce apnea in the fetus with drugs, especially in fetuses with increased motor activity in the presence of meconium in the water. Confirmation of the appropriateness of this is the early work of Goodlin, which found that aspiration syndrome does not occur in newborns whose mothers received sedatives and narcotics. However, this issue requires further study, because the frequency of meconium aspiration syndrome remains high to this day - up to 7%.

Doctors have developed the following method of intra-amniotic fluid perfusion with microfiltration. The amnion cavity is catheterized with a double-lumen catheter, after which perfusion with the baby's own amniotic fluid is started through an external system containing microfilters with a hole diameter of 4 μm, at a rate of 10-50 ml/min until the baby is born. A sealing cuff is brought to the presenting part of the fetus, allowing for long-term perfusion without significant loss of amniotic fluid.

In 29 cases of significant meconium admixture in the amniotic fluid in the first stage of labor, its complete purification occurred 60-80 minutes after the start of perfusion in the absence of repeated meconium entry. Repeated meconium entry was detected in 14 women in labor (49%). In these cases, complete purification of the perfusion system also occurred within 60-80 minutes. In parallel with the microfiltration of the water, given that the presence of meconium may serve as a sign of possible onset of fetal asphyxia, periodic monitoring of the fetus's condition was carried out using the Zaling test. Indeed, signs of fetal hypoxia were detected in 24 women in labor based on pH, pO ₂ and pCO ₂ of fetal blood. In these cases, one of the methods for treating fetal hypoxia was used using antihypoxants, antioxidants and other agents. Perfusion was continued in cases of sufficient effectiveness of antihypoxic therapy. In 22 women in labor (76%) with a satisfactory condition of the fetus during labor, the intra-amniotic perfusion method was used from the moment meconium was detected until the birth of the child, with the average duration of perfusion being 167 minutes.

The condition of the newborns according to the Apgar scale corresponded to 8-10 points in 18 cases (82%), in 4 observations (18%) - 6-7 points. There were no cases of perinatal mortality. No respiratory distress syndrome or external respiration disorders were detected in children during their comprehensive examination in the next 10 days.

Considering the high incidence of respiratory disorders in newborns with the presence of meconium in the amniotic fluid, the method of intra-amniotic perfusion of amniotic fluid with its microfiltration can become an effective preventive method when detecting an admixture of meconium in the waters in the first period of labor and with sufficient therapy for hypoxic conditions of the fetus, which often occur in these cases.