Aortocaval compression syndrome is a complex of hemodynamic disorders caused by aorto—caval compression when the uterus is enlarged. It is manifested by dizziness, sudden weakness, tachycardia, difficulty breathing, a significant drop in blood pressure, increased movements, fainting that occur in the position of a pregnant woman lying on her back. It is diagnosed by echocardiography, dopplerography of placental blood flow, integral rheography. Does not require special treatment. In most cases, it is enough for a woman to change her position in bed to correct her condition. Vertical delivery is recommended to exclude acute intranatal fetal hypoxia.
I87.1 Compression of veins
Aortocaval compression syndrome (ACCS, postural hypotensive syndrome, hypotensive syndrome on the back) is one of the most frequent hemodynamic disorders detected during pregnancy. According to various authors, in the third semester, subclinical manifestations of the disorder of varying severity are detected in 70% of pregnant women, while only about 10% of patients complain of health disorders. The relevance of timely diagnosis of ACCS is associated with an increased risk of termination of gestation and the occurrence of other serious obstetric complications accompanied by a violation of the normal development of the child and an increase in perinatal mortality.
Aortocaval compression syndrome during gestation is usually caused by mechanical compression of venous vessels by an enlarged uterus and a general increase in intraabdominal pressure. Extremely rarely, the blood flow in the inferior vena cava is disrupted due to a combination of pregnancy with other causes – congenital narrowing, thrombophlebitis, volumetric neoplasia of the abdominal cavity, retroperitoneal space, liver diseases. By the end of pregnancy, the mass of the uterus increases 10-20 times, the weight of the fetus reaches 2.5 kg or more, the volume of amniotic fluid is 1-1.5 liters. As a result, the elastic vascular wall, when the patient is on her back, experiences a pressure of 6-7 kg, which leads to a decrease in the lumen of the vein.
Although this situation occurs in almost all pregnant women, the typical clinical picture of ACCS is observed only in 9-10% of patients, and in 17-20% of women the disease occurs subclinically. In the course of research, specialists in the field of obstetrics and gynecology have found that the following predisposing factors increase the likelihood of developing a disorder during pregnancy:
- Insufficiency of collateral circulation. Normally, to compensate for impaired blood flow, a network of paravertebral and unnamed venous plexuses is formed in the NIP system, providing blood discharge above the compression site or into the superior vena cava. With insufficient development of collaterals or their accelerated reduction under the influence of unidentified causes, a hypotensive postural syndrome occurs.
- Undifferentiated connective tissue dysplasia. With a genetically determined violation of collagen synthesis and its spatial organization, the middle shell of the veins is less resistant to external compression. The situation is aggravated by gestational hormonal restructuring. An increase in the concentration of progesterone by 10 times or more leads to relaxation of the smooth muscle fibers of the outer shell of the vena cava.
- Pathological gestation. NSAIDs are more compressed during multiple pregnancies, polyhydramnios, gestation of a large fetus that has arisen against the background of rhesus conflict, congenital anomalies of the child, extragenital diseases (diabetes mellitus, cardiopathology), etc. Almost a third of pregnant women with CPV suffer from vegetative—vascular dystonia, 15% — arterial hypertension, 17% – gestosis, 22% are overweight.
With aortocaval compression syndrome, the outflow of blood from the lower extremities, abdominal and pelvic organs becomes more complicated. Venous return is reduced, respectively, less blood enters the pulmonary alveoli, its oxygenation decreases, hypoxemia forms. At the same time, the cardiac output and the vascular pressure depending on it decreases. Due to the entry into the systemic circulation of a smaller amount of blood insufficiently saturated with oxygen, tissue hypoxia develops in various organs of the pregnant woman and the child. Part of the plasma is deposited in the vascular bed of the lower extremities and loose tissues of the genitals, which contributes to varicose veins.
In two-thirds of patients, the disorder is asymptomatic or with increased fetal motor activity when the position of the woman’s body changes. Signs of postural hypotension usually first appear at 25-27 weeks of gestation. Pathological symptoms appear 2-3 minutes after the pregnant woman lies on her back, and reaches a maximum for 10 minutes. It is extremely rare for ACCS to be observed in a sitting position. More than half of the patients with a clinically pronounced disorder complain of dizziness, a feeling of lack of air, difficulty breathing, sudden weakness, palpitations, more frequent and strong movements. 37% of patients experience a spontaneous desire to turn over on their side, stand up. Sometimes there is precardial pain, noise or ringing in the ears, sparks in front of the eyes, loss of visual fields, anxiety, fear. 1-3% of patients have a significant drop in blood pressure (up to 80 mmHg and below), leading to fainting. Symptoms disappear quickly after changing the position of the body.
ACCS is often complicated by a violation of placental blood flow with the occurrence of chronic or acute fetal hypoxia, a delay in its development. In women with a compressed inferior vena cava, the placenta is significantly more often prematurely exfoliated. Venous stagnation provokes the onset of hemorrhoids, varicose veins, thrombosis, thrombophlebitis. When depositing large volumes of blood in the vessels of the lower extremities, hypovolemic shock with multiple organ damage is possible — impaired renal glomerular filtration, respiratory distress syndrome, cerebral and cardiovascular insufficiency.
Aortocaval compression syndrome is usually diagnosed on the basis of a decrease in blood pressure and characteristic symptoms that occur in the position of a woman on her back. If a subclinical course of the disorder is suspected, a comprehensive examination is prescribed to identify changes in hemodynamics and disorders of fetal blood supply. To confirm the diagnosis , the following are recommended:
- Echocardiography. During the EchoCG study, the change in indicators is evaluated when the pregnant woman turns from her left side to her back. The presence of latent postural hypotensive syndrome is indicated by a 15-20% drop in stroke volume, minute blood volume, cardiac index, increased heart rate, violation of other indicators that reflect the pumping function of the heart.
- Dopplerography. The results of ultrasound of uteroplacental blood flow are also evaluated taking into account the position of the patient’s body. When a woman turns on her back as a result of caval compression, the resistance index (IR) in the umbilical artery is 1.15-1.29 times higher than the normative indicators. At the same time, IR decreases by 10-19% in both uterine arteries.
- Integral rheography. Noninvasive registration of changes in tissue resistance to high-frequency current allows you to quickly assess the blood supply of the vascular bed. Rheographic determination of shock and minute blood volumes, heart rate, cardiac index confirms the results of echocardiographic examination or, if necessary, replaces it.
Taking into account the increased risk of fetal hypoxia, dynamic monitoring of his condition using CTG, phonocardiography is recommended. According to the indications, a spectrophotometric analysis of the gas state of the blood of a woman and, in exceptional cases, a child is performed. Usually, this method reveals a decrease in the partial pressure of oxygen, an increase in the partial pressure of carbon dioxide and signs of metabolic acidosis.
Differential diagnosis is performed with other disorders in which the inferior vena cava is compressed — stenosis, thrombosis, neoplasia of the liver, pancreas, uterus, ovaries, kidneys, bladder, retroperitoneal lymph nodes, retroperitoneal fibrosis, Budd-Chiari syndrome with the growth of a blood clot in the inferior vena cava. Exclude pathological conditions that can provoke collapse: vegetative-vascular dystonia, arterial hypotension due to food or drug poisoning, acute infection, arrhythmia, heart failure. According to the indications, the patient is advised by a cardiologist, phlebologist, gastroenterologist, hepatologist, urologist, oncologist.
As a rule, postural hypotension caused by caval compression passes on its own when the patient turns on her side or gets up. Pregnant women with clinical signs of the disorder should sleep on their left side with pillows placed between their legs or under the upper leg. Some women feel better when resting in a semi-sitting position. To reduce venous congestion and improve hemodynamic parameters, moderate physical activity is indicated — walking, exercises in water, yoga for pregnant women. When intrauterine hypoxia occurs, drugs that improve blood flow in the utero-placental complex are prescribed.
The presence of ACCS should be taken into account when planning the delivery method. In the absence of obstetric and extragenital indications for cesarean section, natural childbirth in an upright standing, sitting or squatting position is recommended for patients. This can significantly reduce the risk of fetal hypoxia. If a woman insists on the traditional method of delivery, she is laid on her left side, and during the period of exile she is transferred to a maternity chair with the head end raised high. During operative delivery, caval compression often provokes critical hemodynamic disorders, which is important to remember during preparation and during the intervention.
Prognosis and prevention
The outcome of pregnancy and childbirth with timely detection of ACCS is favorable and becomes serious only if the patient does not comply with the recommendations of an obstetrician-gynecologist for lifestyle correction. For preventive purposes, all pregnant women after the 25th week are shown to refuse to sleep and rest on their backs, reduce excess weight, and have sufficient motor activity to maintain normal hemodynamics. Women with polyhydramnios, multiple pregnancies, obesity, varicose veins of the lower extremities, genitals when signs of intrauterine hypoxia of the child appear (increased or slower movements, changes in their intensity) to prevent possible complications, it is necessary to undergo an examination to exclude hidden forms of postural hypotension on the back.