How much do you know about supine hypotensive syndrome?

With the progress and development of society and the relaxation of the national birth policy, the number of pregnant women may increase. Some pregnant women may experience discomfort symptoms such as dizziness, palpitations, nausea, vomiting, etc. when lying in the supine position in the late pregnancy. So what happens to the pregnant women at this time?

1. What is supine hypotension syndrome

Supine hypotensive syndrome refers to a group of clinical syndromes in which pregnant women in the late pregnancy are in a supine position and the enlarged uterus compresses the inferior vena cava, resulting in insufficient blood return to the heart. Pregnant women experience dizziness, dyspnea, nausea and vomiting, chest tightness, pale complexion, cold sweats, rapid heartbeat and varying degrees of blood pressure drop. When pregnant women change their body position to a lateral position, the above symptoms are alleviated or disappear. Supine hypotensive syndrome is a common postural hypotension in clinical practice. Severe supine hypotension can lead to maternal ischemia and hypoxia, followed by fetal hypoxia and acidosis, which seriously threatens the life safety of the mother and fetus. Studies have shown that the incidence of supine hypotensive syndrome in my country is about 30%.

2. Causes of supine hypotension syndrome

The level of blood pressure in the human body is related to factors such as the amount of blood discharged by the heart, circulating blood volume, peripheral vascular resistance, blood viscosity, and vascular elasticity. Supine hypotension syndrome is common in pregnant women in late pregnancy and occasionally in patients with giant ovarian tumors in the abdominal cavity. It is generally believed that it is mainly related to body position. As the gestational age increases, the fetus is also growing. When the pregnant woman is in a supine position, the enlarged pregnant uterus can compress the inferior vena cava, affecting the venous return of the inferior cavity and pelvic cavity, reducing the amount of blood returning to the heart, and the right atrial pressure and cardiac output decrease accordingly, causing a series of manifestations of shock caused by a drop in blood pressure. Clinically, it has been found that pregnant women with abnormally enlarged uterus such as multiple pregnancies and polyhydramnios are more susceptible to this syndrome, which also suggests that its occurrence is related to compression of the inferior vena cava.

In late pregnancy, the diaphragm will also be compressed by the enlarged uterus, causing the vagus nerve to become excited, the heartbeat to slow, and the heart blood vessels to dilate, which also causes a drop in blood pressure. Because the uterus supplies a large amount of blood in late pregnancy, which may reach 16% of the body's blood volume, it may also cause a decrease in the amount of blood flowing back to the heart, which in turn causes a drop in blood pressure.

Some people believe that the occurrence of supine hypotension syndrome is also related to mental and neurological factors and stimulation of the nerve plexus. Studies have shown that for the same cesarean section of the lower uterine segment, the incidence of supine hypotension syndrome in patients undergoing surgery under local anesthesia is about 2%, while that in patients undergoing surgery under epidural anesthesia is as high as 20%. Analysis of the reasons found that epidural anesthesia can block the sympathetic preganglionic fibers, causing the blood vessels within the anesthesia plane to dilate and blood to stagnate, thereby reducing the amount of blood returning to the heart and cardiac output, which is the reason for the increased incidence. It also shows that nerve reflexes can also affect heart function and blood pressure changes. Pregnant women have a disorder of cardiovascular function in the late pregnancy, so they may experience supine hypotension syndrome.

3. Symptoms of supine hypotension syndrome

Symptoms of supine hypotension syndrome are that some pregnant women in late pregnancy will experience shock symptoms after lying supine for several minutes. Symptoms include dizziness, chest tightness, nausea, and vomiting. Examinations may reveal that the patient frequently yawns, sweats all over the body, has a faster pulse, drops in blood pressure, and drops in systolic blood pressure. As blood pressure drops, the fetus is also affected, showing an increase in fetal heart rate and increased fetal movement, followed by a slow fetal heart rate and weakened fetal movement, with acute fetal distress. If the patient lies supine for a long time, the inferior vena cava will be compressed for too long, which can also increase the inferior vena cava pressure and the pressure in the intervillous cavity. Animal experiments have shown that this can cause early placental abruption and bleeding, and eventually severe pregnant women may threaten the safety of mother and baby.

Possible treatment measures

Treatment measures for supine hypotension syndrome include changing body position, adjusting diet, fluid replacement, and others.

Change body position

Patients with supine hypotension syndrome should change their body positions at ordinary times. Try not to sleep in a supine position at night. You can choose to lie on your left side or right side. Changing body positions is conducive to blood circulation, thereby gradually increasing the amount of blood returning and relieving the discomfort caused by low blood pressure. Pregnant women with this syndrome in late pregnancy should be tilted to the left by 10 to 15 degrees or their right buttocks should be raised during cesarean section under spinal anesthesia to resolve the compression of the inferior vena cava by the huge uterus, restore normal venous return, and avoid the occurrence of supine hypotension.

Adjust your diet

Patients who have experienced supine hypotension syndrome should also adjust their diet structure in time. They can consume more foods rich in carbohydrates, protein and vitamins, such as fish, lean meat, milk, etc., and increase their daily water intake and sodium salt intake appropriately to improve the discomfort symptoms caused by low blood pressure.

Fluid replacement

Because upper limb venous infusion is not affected by the compression of the inferior vena cava, the fluid can return to the heart directly through the superior vena cava, thereby increasing the amount of blood returning to the heart and cardiac output. Studies have found that rapid infusion of upper limb veins during lower uterine segment cesarean section can reduce the incidence of supine hypotension syndrome, indicating that rapid infusion of upper limb veins during lower uterine segment cesarean section does have the effect of preventing supine hypotension syndrome.

Other methods

Other methods include medication, compression stockings, and abdominal bandages.

Zhang Huanhuan, Affiliated Hospital of Chengde Medical College

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