I. Can maternal flatlining kill you?
It was recently reported that a 41-year-old obese pregnant woman (height 173 cm, weight 128 kg, pre-pregnancy 113 kg), who was admitted to hospital at 37 weeks with suspected gestational diabetes mellitus and a huge baby due to excessive amniotic fluid, was found dead in her bedroom by her husband on the 9th day after discharge. The deceased was lying flat on her back in bed, and autopsy confirmed dilated jugular veins (in the neck) and subclavian veins (in the chest), atrophy of the inferior vena cava, and dilated and congested veins in the lower extremities bilaterally. The diagnosis of “supine hypotension syndrome” was made as the probable cause of death.
Why do up to 75% of pregnant women experience shortness of breath during pregnancy?
Up to 75% of pregnant women experience shortness of breath during pregnancy, and there are many reasons for this phenomenon, two of which are more important.
1. When lying down, there is little oxygen left in the lungs (shortness of breath)
During pregnancy, the oxygen reserve in the lungs decreases severely because the diaphragm (the breathing muscle between the chest and abdominal cavity) rises to squeeze the lungs.
(1) At full term, it can be reduced by 80% compared to the pre-pregnancy period.
(2) When lying flat, it is further reduced by 70% on top of the remaining 20%.
(3) Also, the oxygen consumption during pregnancy is 40-75% more than before pregnancy.
(2) When lying flat, blood pressure drops and the blood supply (oxygen) to organs is insufficient (nausea)
A drop in blood pressure and insufficient blood supply (oxygen) to the organs can cause breathing difficulties. It will also make the patient feel nausea, vomiting, chest and abdominal discomfort or pain, numbness in hands and feet, visual impairment, tinnitus, headache, dizziness, irritability, etc., and even shock symptoms such as panic, pale or blue face, and false sweating can occur. In more serious cases, pregnant women can faint to death.
Many pregnant women in the middle and late stages of pregnancy sometimes find the above symptoms lying flat on their own, and the patients are willing to bend their knees and hold their legs or turn into a side position by themselves. Obstetricians have long noted these phenomena, and found that, in late pregnancy, pregnant women lying flat, in addition to lower blood pressure, lower limb venous pressure is increased.
Third, after 20 weeks of pregnancy, must not lie flat
Although, the gestational uterus began to come out of the pelvic cavity at 12 weeks, but generally to 20 weeks, the bottom of the uterus can be felt at the level of the navel, that is, the uterus really into the abdominal cavity.
Therefore, pregnant women after 20 weeks of pregnancy must not lie flat, no matter what time of the day. Especially some high-risk patients, such as: premature birth, multiple births, huge babies, obese and other pregnant women. Pay more attention when exerting yourself, because generally speaking, hypotension occurs within 3-10 minutes after lying flat, in case you fall asleep during this time, there is a real possibility that you will never wake up again.
Health care providers should also be especially careful to keep the woman’s uterus in a left-sided tilted position all the time during labor and delivery. During cesarean delivery or non-obstetric surgery after 20 weeks of gestation, the first thing to do when the patient crosses to the surgical bed is to elevate the patient’s right side across. Otherwise, under general or lumbar anesthesia, vasoconstriction compensatory capacity is reduced. It has been reported in the literature that because of this loss of compensation, the drop in blood pressure caused by lumbar anesthesia combined with “supine hypotension” may lead to circulatory collapse and death of the patient after lumbar anesthesia for cesarean delivery.
Fourth, what is supine hypotension syndrome?
Here, I mainly talk about blood pressure, blood pressure refers to the usual doctor to measure your arterial blood pressure.
In the 1930s-1950s, there were many such cases reported in the medical literature. It was not until the 1950s and 1960s that doctors figured out what caused this phenomenon and named it “supine hypotension syndrome” due to compression of the aorta (large artery in the abdominal cavity) and the inferior vena cava (large vein in the abdominal cavity).
The venous blood in the lower extremities normally returns to the heart through the inferior vena cava in the abdominal cavity.
1, as the month of pregnancy increases, the uterus also grows, to you can feel their own uterus, about 20 weeks of pregnancy, the uterus has entered the abdominal cavity from the pelvis. Then, when you stand or lie on your side, the uterus will not press on the inferior vena cava.
2, When you lie flat, the uterus will compress the inferior vena cava (the venous pressure is lower than the arterial pressure, and the venous wall is thinner than the arterial wall, so, it is easy to be compressed), so that the venous blood of the lower extremities cannot return to the heart completely, and at the same time, it causes the venous blood pressure of the lower extremities to rise. Without blood back to the heart, the heart beats more powerfully, but also can not deliver anything to the whole body. The heart can’t pump enough blood, it will make the blood pressure drop, and pregnant women will have all the symptoms mentioned above.
3.When you actively turn into side lying position, the inferior vena cava is no longer under pressure. When you bend your knees and hold your legs, you can increase the venous pressure in the lower limbs and overcome some of the lack of blood return to the heart caused by the pressure in the inferior vena cava, so you will feel some relief from the symptoms. When lying flat, in addition to the compression of the inferior vena cava, scientists later found that the aorta in the abdominal cavity was also partially compressed.
4, causing insufficient perfusion of blood to the distal branches of the arteries (such as the uteroplacental artery and the arteries of the lower limbs).
5, Insufficient blood flow to the uteroplacenta may lead to placental abruption and fetal hypoxia.
The drop in blood pressure may also cause inadequate cerebral oxygen supply and reduced renal blood perfusion in pregnant women, together with uterine compression of the ureter, resulting in reduced urine output.
How to deal with “supine hypotension syndrome” caused by aorta-inferior vena cava compression?
Many pregnant women instinctively lie on their sides to relieve their discomfort, which tells us the answer.
Clinical trials have also confirmed that elevating the pregnant woman’s right crotch and tilting the pelvis 15-30 degrees to the left, although not completely relieved, can reduce aortic-inferior vena cava compression, thus effectively reducing the complications of compression of these vessels.
Babies born to mothers in the 15-degree tilt position have better cord blood chemistries and clinical scores compared to those born to mothers lying flat. If the left tilt of the uterus does not relieve the patient of symptoms or fetal heartbeat abnormalities, the patient can be placed in a completely left lateral position or try to keep the patient’s left crotch padded so that the uterus tilts to the right.
In short, the angle and direction of the pad should be adjusted according to the patient’s specific situation. If there is no special water bladder air bag, we often use a large pillow or rolled up blanket, the right side of the pregnant woman’s waist and crotch together with high, so that the patient does not twist the waist uncomfortable.
Sixth, the incidence of “supine hypotension syndrome” is not 100%, why?
Because when the aorta and inferior vena cava are obstructed, our body has some ways to cope.
1. create more arteriovenous collateral circulation to allow blood flow to bypass the obstructed area.
2. nerve reflexes will compensate by increasing vasoconstriction to raise blood pressure, etc.
3, the degree of lumbar spine protrusion varies in pregnant women, and the pronounced protrusion makes the inferior vena cava less likely to be compressed.
However, we have no way to determine which individuals have sufficient arteriovenous collateral circulation to compensate for the obstruction of the inferior vena cava of the aorta; which individuals have sufficient neural reflex activity to cause vasoconstriction to normal blood pressure; and we cannot predict the relationship between the spine and the uterus, the shape and the degree of softening of the uterus in different individuals.
Also, experiments have confirmed that lower extremity (femoral) and (N) arterial pressures perfused by the lower branches of the abdominal aorta can be reduced when upper extremity arterial pressures are normal. In other words, even if the blood pressure measured in the upper extremities of the mother is normal, this does not exclude the possible lack of blood flow to the uterus and fetal damage caused by compression of the abdominal aorta.
Does “supine hypotension syndrome” affect painless delivery?
”Supine hypotension syndrome occurs in about 30% of pregnant women and is more common in patients with labor analgesia or intravenous anesthesia, which can cause a decrease in blood pressure.
However, this is not to say that we do not advocate labor analgesia or intralesional anesthesia. On the contrary, we believe that the benefits of labor analgesia for the mother and fetus outweigh the harms and actively encourage epidural labor analgesia for women. “Supine hypotension syndrome can be prevented, and hypotension caused by labor analgesia or intralesional anesthesia can be treated. Moreover, anesthesiologists are paying more attention to this area, and there are reports in the literature of increased overall safety for mother and baby.
Therefore, to ensure the safety of each mother and fetus, we require that all pregnant women over 20 weeks of pregnancy maintain a left-sided uterine position.